Avia Tips from A to Z
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AVIA Calibration Tip #1 - Needle Pulses + Steps Video Test Pattern
Needle Pulses + Steps Test Pattern
At first glance, one mistakes this pattern for a traditional Needle Pulse pattern, but
there are important changes in the pattern which make it more useful. Most obvious is the
addition of a vertical line on the right side of the pattern. The traditional pattern only
has a line on t he left side of the pattern. By adding the right side line, AVIA makes it
possible to look for closely for high voltage supply problems. Often geometry distortion
with high voltage system overload appears worse and earlier along the right edge. Without
the right side line, traditional Needle Pulse patterns don't allow you to visualize the
change. You might be fooled into thinking a display has perfect geometry stability when in
fact it is distorting the image.
Another obvious addition are the gray scale steps in the upper half of the pattern. On
CRT displays one looks for both geometry distortion AND blooming in order to find the
maximal usable white level setting. This used to require two separate test patterns. By
adding the gray scale steps, AVIA makes it possible to look for both changes with a single
pattern. No more switching back and forth between patterns.
If you also observe the upper and lower halves of the Needle Pulses pattern closely,
you'll notice some bars moving back and forth. The "Black Bars" in the upper
half of the pattern are useful for checking the black level (brightness) setting of your
display. The "white bars" in the lower half of the pattern are for testing white
clipping level of LCD projectors. This means a single pattern allows for testing of three
limits of white level and a quick check of black level.
For those who prefer a more traditional pattern, AVIA also includes the Needle Pulses
pattern which omits the gray steps but includes the black bars and white bars. I can't
really imagine why one would want to omit the test for blooming, but AVIA provides you the
AVIA Calibration Tip #2 - Blue Bars, Red Bars, Green Bars
Color bars are useful for checking the proper function of color decoders in a display.
With NTSC displays one can vary the saturation (amount) and hue (phase relationship) of
the display. Ideally, the display is adjusted to recreate the same colors as encoded in
The traditional SMPTE color bar includes not only bars but small patches of colors
which are in reverse blue order just below the color bars. By examining the amount of blue
(using a filter or better yet by using the display's blue only mode) one can tell if the
saturation and hue are correctly adjusted. This works because the gray portions of the
pattern are encoded to be an intensity of gray which has exactly the same amount of blue
in the blue portions of the pattern. Since gray contains no color content, turning the
saturation control up and down does not affect its blue content. This allows the gray to
act as a reference point against which to compare the amount of blue is present.
Calibrating saturation can thus be done by adjusting blue intensity to match the fixed
amount of blue in gray. Hue is observed by comparing the amount of blue in the magenta and
cyan portions of the pattern. When hue is correctly adjusted, the blue intensities of
magenta and cyan are identical.
Unfortunately, some people find it difficult to accurately tell when the blue
intensities are equal. The bars and patches are of unequal size and color separation
artifacts can make the color transition zones blurred or of uneven darkness. For these
reasons, AVIA's "Blue Bars" add flashing patches within the color bars to aid in
finely discerning when the intensities are equal. Human vision is very sensitive to
flashing. AVIA takes advantage of this by having users adjust saturation and hue to
minimize visible flashing in blue. This allows higher accuracy than comparison of static
bars and patches. For those who still prefer more traditional static comparisons, AVIA
also provides traditional split color bar patterns.
Several other features are built into the color bars. You may not have noticed that the
transitions between bars and patches is closer to the center of the screen than SMPTE
bars. This moves the critical comparison area of the pattern further from on screen
displays which often appear at the bottom of the screen when televisions are adjusted. The
white reference rectangle at the bottom of the pattern includes animated white bars for
detecting white clipping. The lower right black portion of the pattern has animated black
bars for checking black level. These are positioned where the PLUGE pattern is on SMPTE
bars, but animation avoids the optical illusions of aligned rectangle edges that sometimes
make it difficult to tell if a PLUGE rectangle is visible. Animation makes visibility
obvious. Also the black bars do not rely on a blacker than black component for proper use.
However, the black bars in this pattern are only to be used on displays which need a high
APL during black level adjustment.
One can also use SMPTE bars in red or green only, but AVIA makes evaluation of green
and red primary handling by providing "Red Bars" and "Green Bars."
These are used in the same manner as the blue bars, except one views the red bars in
red-only and the green bars are to be viewed in green-only. The patches which need to be
compared are also moved to be positioned below the bar against which comparison needs to
be made. This makes intensity comparisons easier than the wide separations that arise with
a blue optimized color bar pattern. AVIA also adds its innovative flashing patches to the
red and green bars to enhance viewer accuracy.
Why red and green bars? If the color decoder is perfect, adjusting to blue only
accuracy would make the red and green color bar patterns also appear perfect.
Unfortunately, it often isn't perfect. We'll visit that in AVIA Calibration Tip --- Color
AVIA Calibration Tip #3 - Sharpness Pattern
NTSC video carries most of its resolution in the luminance portion of the signal. Onto
this is overlaid lower resolution color information to yield the final picture. By doing
this, the designers of the NTSC system were able to provide an image which gave much of
the perceived effect of having high resolution in both color and luminance but in a
smaller amount of bandwidth.
Television displays provide a sharpness or peaking control whose behavior is much akin
to the treble control of an audio receiver. The control should be used to compensate for
the attenuation of high frequency video information that blurs images horizontally.
Unfortunately, this control is often misused or not designed in a way that accomplishes
this goal. Users often keep sharpness set too high and suffer a picture that appears
sharper to the naïve eye, but is actually filled with extraneous image artifacts.
Sharpness is perhaps the most difficult control to teach people to set properly.
There are often recommendations to simply turn sharpness all the way down, but that can
be excessive. It's best to actually use a test pattern which points out how the sharpness
control is altering the image. Then you can rationally determine optimum setting on your
display. AVIA provides a dedicated Sharpness pattern which combines several tests of
parameters important in determining optimal sharpness setting.
- A horizontal frequency sweep occupies the top of AVIA's sharpness pattern. This is a
constant amplitude sweep that goes from low video frequency to high video frequency. If
the video bandwidth of your display is lower in a portion of the video bandwidth, then
that section of the sweep appears darker. Ideally, the brightness of the sweep is constant
throughout its range. As you adjust sharpness up and down, look to see if any portion of
the sweep goes up and down in brightness. That is the set of video frequencies the
sharpness control of your display affects. If your display's sharpness control is well
designed, all you need do is adjust to make the sweep as evenly bright as possible.
- Some people find it difficult to compare different sections of a sweep because the
gradation of brightness is continuous from one section to another. The frequency bursts at
the bottom of the chart provide discrete patches of video frequencies that can be
compared. You'll probably find that the rightmost patch is slightly darker than the rest
of the patches even on the best of displays. Just try to equalize the other patches.
- There are black vertical lines, diagonal lines, and a circle in the center of the AVIA
sharpness pattern. These are needed because many sharpness controls not only alter
frequency response but add ringing artifacts. Ringing is overshoot and undershoot of the
video signal at abrupt luminance transitions. You see this as false outlines next to the
actual black lines. If setting sharpness at the point which equalizes video bandwidth also
yields visible ringing, you should decrease sharpness to the point at which the false
outlining is just barely visible. Otherwise, you will be adding artifacts rather
sharpening actual image detail.
- There are also vertical lines set against black and white backgrounds. These are also
used to look for ringing, but because the luminance transitions are larger than going from
a gray background to black, these serve as especially severe tests for ringing. These are
primarily for testing display circuit design quality rather than for actually setting the
sharpness control, because these are usually too severe a test for consumer grade
displays. Setting sharpness low enough to avoid all outlining of black/white transitions
will often yield an excessively blurred image on consumer grade displays.
- A vertical frequency sweep occupies the left side of the pattern. This is used in
conjunction with the horizontal lines of the pattern to set vertical aperture (vertical
sharpness) of video processors which have this control. As with the usual sharpness
control, adjust to equalize video bandwidth and avoid false outlining.
Once you have correctly set sharpness, it is very tempting to return to your previous
excessively high setting. Don't. Instead, view the picture several days at the new, less
artifact inducing setting. You will find that the old overly high setting yields an
Properly adjusting the sharpness control is only part of getting maximal image detail
from your display. Keeping white level below the point of blooming and controlling room
lighting should also be done. Once all these are done, you might wish to measure your
display's resolution using resolution patterns which I'll cover in another AVIA
AVIA Calibration Tip #4 -- Color Decoder Check
NTSC video signals must be separated, decoded, and matrixed to form the final red,
green, and blue signals which drive the display. Professional grade displays accurately
decode the color signals and render colors correctly. However, consumer grade televisions
often break the rules and have non-standard color decoding. This is most often seen as
exaggerated reds (red push) and wreaks havoc when one attempts to adjust colors on a
consumer display using just color bars.
Color bars are encoded such that the amount of red, green, or blue is 75% in each bar
which contains the color. For instance the amount of blue is 75% in the gray, blue, cyan,
and magenta portions of color bars. Similarly, the amount of red is 75% in the gray, red,
yellow, and magenta portions. Because the amounts of each primary are identical in the
various patches, one can compare the intensity of each color to learn how a decoder is
functioning. AVIA also includes 50% & 100% color bars for testing of color circuitry
linearity but we'll ignore those for now and concentrate on the more commonly used 75%
variety of color bars.
75% Gray has zero color difference from gray so adjusting color saturation up and down
doesn't alter its appearance. Hence, gray serves as the reference point against which the
intensity of color saturation may be compared. Turning saturation up and down alters the
intensity of the colored portions of color bars. View the blue portions of color bars in
blue-only as you increase saturation. You'll notice that blue increases in intensity with
increasing saturation. When saturation is correctly set, the intensity exactly matches
that of gray. On a professional display with NTSC accurate color decoding, this same
saturation setting also makes the red and green portions of the pattern match gray. Hue is
adjusted by comparing portions of the pattern that contain two primaries such as cyan vs
AVIA has a Color Decoder Check pattern which lets you measure and compensate for
non-standard color decoding. The pattern has a gray background against which you compare
the brightness of red, green, and blue color patches. The patches range from +25 to -25%.
If the color decoder is perfect, then the 0% patches of each color match the gray
background (when viewed in only that color). If a display has red push, then a higher
(darker encoded) red patch matches the gray background. You can read the percentage push
by finding the patch which best matches the gray.
You may find other imbalances with the AVIA Color Decoder Check pattern, but red push
is the most important to control. This is because red push is more objectionable to most
viewers than under push or green push. A professional calibrator can sometimes correct the
color decoder axes to achieve NTSC standard decoding, but for most sets that is not
possible. You may want to check the accuracy of color decoding of a display prior to
purchase since this problem is often not correctable. The only recourse is to hide (not
correct) the error by decreasing saturation to make the measured red push 10 to 20%. This
desaturates the overall picture but avoids making flesh tones too orange. Leave hue alone
when making this compensation.
There are two other things to remember when considering non-standard color decoding.
Don't confuse correcting the color decoder axes with resetting gray scale. This problem
cannot be corrected by decreasing red drive because that would alter the underlying gray
scale of the picture. The problem is with the way color DIFFERENCES from gray are being
interpreted by the display's color decoder, not with the amount of red in the gray scale.
The second thing to remember is that this pattern and color bars are most accurate if
one turns off the other two color guns of the display when examining each color. Color
filters leak through a bit of the other colors and falsely make the gray background
brighter than it really is. This tends to make your observations through filters about 5%
lower than if color filtering were perfect. The difference is small, but if you want
highest accuracy, turning off or capping the other two color guns is best.
AVIA Calibration Tip #5 -- Resolution Patterns
Look in your local newspaper advertisements and you'll see amazing claims of 800 to
higher lines of resolution. Unfortunately, you'll be hard pressed to find a salesman who
understand how those numbers were measured or how they relate to the display's actual
ability to display fine image detail. One problem is that there is no legal standard for
how the number must be derived and reported. A manufacturer could theoretically bypass
most of the display's electronics and simply measure the performance of the best amplifier
section. In the final analysis, you need to either rely on magazine reviewers to measure
true TVL or learn a little about the resolution patterns in AVIA and measure it yourself
before you buy a set. The test patterns in AVIA can serve as a powerful means of
separating the chaff from the wheat when you're shopping.
TVL (TV Lines) resolution is expressed as the number of vertical black and white lines
(counting both black and white) which can be resolved across a width of screen equal to
the height of the screen. This differs from computer graphics in which horizontal
resolution is measured across the entire screen rather than just a width equal to the
height. For a 1.33:1 ratio screen (4:3), this means that TVL resolution is 3/4 the number
of discernible lines across the entire screen width. On a 1.78:1 ratio screen (16:9), the
TVL resolution is 9/16 of the number of discernible lines across the entire screen.
Exercise: You are writing advertising and press copy for a new projection television.
What resolution number would you state, if your engineers tell you the following?
- Lenses in the optical system have a maximal theoretical resolution of 1100 lines.
- The final video amplifier stage (bypassing most of the electronics) can resolve 800
lines across the entire screen.
- The overall electronics & optics resolves 600 lines across the entire screen width
- The TVL resolution is 450
Remember, there aren't any legal requirements on how you report the resolution. Would
you say that your display only has 450 lines of resolution?
So now we see how "lines of resolution" can mean different things if one
doesn't specify how they are being expressed and measured. For actually viewing images,
the overall TVL resolution is the most meaningful.
Some people are confused because they also know that NTSC video has a fixed number of
scan lines of which about 480 are visible on screen. If the number of scan lines are
fixed, then how can lines of resolution vary from set to set? The answer is that TVL
resolution is measured along the HORIZONTAL direction, not the vertical direction. It's a
totally different performance parameter. As long as the deflection and synchronization
circuitry is working correctly, you'll always have the correct number of scan lines
(ignoring overscan). The TVL resolution, on the other hand, is critically affected by the
quality of the video circuitry and how high frequency video information is preserved. If
video bandwidth is limited, then fine image details blur or are completely lost.
I should also mention that TVL resolution refers to luminance resolution in NTSC video.
This is because NTSC video carries most of the fine picture information in the luminance
channel and very low resolution information for color transitions.
Now it's time to examine AVIA's resolution patterns. There are three resolution
patterns supplied in AVIA. They are the WSE Resolution, 100 TVL Resolution, and 200 TVL
Resolution patterns. Along with AVIA's multiburst and sweep patterns they are used to
measure how well a display resolves fine detail.
The resolution patterns are similar so we'll cover them together.
The pattern has a gray background and markers which indicate percent overscan. The
innermost rectangle represent 5% overscan from each edge. In the very center of the
pattern is a zone plate pattern consisting of concentric circles of varying spacing. Four
resolution wedges are also in the inner portion of the pattern. The outer four circles
serve as corner geometry checks and also lines which are spaced at frequencies of special
The Zone Plate portion of the pattern is a test of color separator performance. If you
play this pattern through the composite input of a display, the varying angles and spacing
of the concentric circles severely test the ability of the display's color separator
(often a comb filter) to cleanly separate color and luminance portions of a composite
signal. Perfect separation would produce concentric circles without any coloration or
disappearance of sections of the concentric circles. You can see how perfect separation
appears if you view this pattern via S-video or component connections. Most comb filters
produce some cross color (rainbowing). The better the comb filter, the less cross color is
present. Some displays cheat and include a notch filter which removes information near
3.58 MHz. This can avoid cross color but dramatically limits image detail.
The following assumes a COMPOSITE connection so you can test the color separator.
The 3.0, 3.58, 4.18, and 6.75 MHz corner circles all contain vertical lines spaced at
that frequency. 3.58 MHz is the NTSC color carrier frequency and serves as a very severe
test of color separation. 4.18 MHz is near the maximal broadcast resolution, and 6.75 MHz
is the maximal resolution possible on DVD video. Many consumer displays don?t have
sufficient resolution to display the finely spaced vertical lines in the 6.75 MHz circle.
Front projection systems usually have enough TVL resolution to show the individual fine
The 3.0, 3.58, and 4.18 MHz circles also have their lower halves filled with diagonal
lines at the same horizontal frequency. This is another test of comb filter type. There
are several designs of comb filters available and they differ in their ability to avoid
cross color. Fairly simple comb filters (1 or 2 line) can avoid cross color on vertical
lines (even at the worse case 3.58 MHz), but cannot avoid cross color on diagonal lines.
It takes a high grade "3D" comb filter, which uses information from more than
one video frame, to avoid cross color in diagonal lines. This is why I included diagonal
lines in the lower halves of the corner circles. BTW, the 6.75 MHz circle does not have
diagonal lines in the lower in its lower half.
Vertical and horizontal wedges of lines (actually sinusoidals) which converge closer
and closer together are used to measure resolution. Use either of the vertically oriented
wedges to measure horizontal TVL. Find the point in the wedge at which the lines cease to
be separate and blend together. Then read the scale markers to find your display's actual
You could use a similar pattern (SMPTE Resolution) in Video Essentials. However, that
pattern is older and ends at 500 TVL so it cannot test if your display is fully resolving
DVD's maximal detail because the pattern never attains the limit. AVIA's resolution
patterns reach the full DVD video limit or 540 TVL (6.75 MHz) and allow you to see if your
display is capable of showing the full degree of DVD resolution. On a related note, one
should not use the VE multiburst or sweep patterns to check DVD player frequency response
because both those VE patterns fall off rapidly at high frequencies. In contrast, the AVIA
multiburst and sweeps maintain nearly full amplitude out to their limits because they were
synthesized directly in the digital domain. They also contain built-in markers for -3 and
-6 dB signal attenuation. This is important for setting up video processor and doing
equipment reviews, but I digress.
The horizontal wedges are used to measure vertical resolution. Unless you display has
markedly poor vertical synch timing, you should see the full 480 scan lines resolved. Some
interlace flicker is likely visible in the horizontal wedges.
One final experiment is worth doing while viewing the resolution pattern. Watch the
vertical wedges while you turn your display's sharpness control up and down. You'll see
the line spacing (frequency) at which the control has its greatest effect go up and down
in brightness. When sharpness is adjusted to flatten video frequency response, the
vertical wedges have even brightness from top to bottom. However, you still may need to
compromise video frequency response to avoid ringing artifacts.
Now for the differences between the three AVIA wedge patterns:
The 100 and 200 TVL patterns differ only in the starting points of their resolution
wedges. You can use either, but the 200 TVL pattern was supplied to allow finer
measurement of TVL resolution in the range of most consumer displays.
The WSE (widescreen enhanced) resolution pattern is used like the 100 and 200 TVL
patterns, but the display must be in 16:9 enhanced mode AND the DVD player must be set to
16:9 shaped video display.
I'll leave you with two study questions: If you can solve these, you understand how TVL
resolution is defined. The answers are below, but do try to solve these yourself.
- Given that the pixel map in NTSC DVD video is 720 x 480, why is the TVL limit 540 on a
1.33:1 (4:3) screen?
- Is the TVL limit the same on a 1.78:1 (16:9) screen?
- The TVL is defined over the width which equals the height. That is 720 x 3 / 4 = 540. 2.
- On a 1.78 screen, the height is smaller relative to the width, but the full width is
still 720 pixels. Hence, TVL resolution max on a 1.78 screen = 720 x 9/16 = 405. This is
why the WSE resolution pattern's wedges end at 405 rather than 540 TVL.
AVIA Calibration Tip #6 -- Subwoofer Test Tones and Bass Management
AVIA users have occasionally wondered why nothing comes out of their subwoofers during
AVIA's subwoofer setup test tones unless their speaker sizes are set to "small."
The test signals are working as they should, but AVIA is probably the first test material
you've encountered which starkly reveals the effects of bass management. The subwoofer
test tones in AVIA do not DUPLICATE the low bass information from the five main channels
(front left, center, front right, surround right, surround left) into the LFE track. We
could have duplicated the low bass information into the LFE track. This would have yielded
subwoofer output whether one set speaker size to "large" or "small,"
but would also completely obscure how bass management is actually working. With AVIA, what
you get at your subwoofer is only what the bass management system in the receiver is
doing, not what we put in the LFE channel. Duplicating the low bass information into the
LFE channel would make more systems APPEAR to function as users expected, but wouldn't
clue them into what is actually happening in their system's bass management.
You may well discover that setting main speaker sizes to "large" completely
stops a receiver's bass management from routing low frequency information in the main
channels to the subwoofer. This means a lot of people are finding out that the bass
management in their receivers isn't quite doing what they believed. Actually getting low
bass information from the main channels to the subwoofer often requires one to set the
speakers sizes to "small." Most users don't expect this to be true in their
equipment and are shocked to find nothing coming out of their subwoofer when speaker size
is set to "large." ----- > If your system behaves this way with the AVIA
subwoofer test tones, this is also what it does to low bass in the main channels of a
movie sound track. < ----- You may not have realized that you have been relying on only
your main speakers to reproduce low bass in the main channels and the subwoofer has ONLY
been producing low bass from the LFE channel. AVIA's subwoofer setup tones reveal this
facet of bass management.
Many receiver and speaker systems are actually more appropriately set to
"small" size despite their having "full range" speakers. This allows
the subwoofer to receive and reproduce low bass from all the channels rather than only the
LFE. The "large" setting implies that the speakers are capable of reproducing
the pounding LF effects one usually gets from a subwoofer in a home theater setup. At
least try it both ways to see which yields better results in your system.
Sometimes bass management limitations make it objectionable to set speakers to
"small." Perhaps one has full range main speakers, a high crossover frequency in
the receiver, and a sub which does not integrate well in the low-mid bass. The resultant
gap in coverage is difficult to fix. A more flexible audio processor or some creative
feeding to the sub of bass from main speakers (set to large) + bass from the LFE track may
be needed. Two channel listening of music also comes to mind as a special situation.
AVIA's subwoofer setup tones reveal how your equipment's bass management system
actually deals with low bass. This gives you a chance to understand and optimize bass
management on your equipment.
Black and White Level Adjustment
Let's first examine what the black level (brightness) and white level (contrast)
controls actually do inside the set and the performance limitations that set the bounds
within which you should keep the controls.
Within the television, there are video amplifier stages. Somewhere near the end of the
video signal processing chain, just before the signal reaches the final amplifiers, the
black level and white level controls operate. At the amplifier stage where these two
controls operate, a small video signal undergoes amplification before being passed to the
next circuitry stage. The higher the signal, the higher the associated beam current and
hence more light output. (I'm ignoring the inverted polarity of the signal to simplify
Essentially, the black level control sets the baseline (bias) level of the amplifier
stage. Think of it as setting what the lowest point (black) upon which the rest of video
signal rides. The white level control sets how much amplification is performed on the
signal. A higher white level setting means that video signal excursions are larger.
The combination of black level and white level controls allows you to control the
amplitude and baseline of the video signal. If the display were capable of unlimited light
output as video signal amplitude increases, one would only have to worry about light
output and the blackness of black when setting these controls. Real life displays have
limitations and exceeding these limits can damage or shorten a display's life.
I'll concentrate on CRT displays for now. The video signal is processed and eventually
delivered to the red, green, and blue electron guns. A higher signal makes the gun emit
more electrons and produce a brighter spot on the screen. CRT's are limited in how much
beam current can be safely used. If too high an output is attempted, the phosphor at the
front of the screen can be physically damaged by the electron beam. It isn't practical for
you to measure the beam current so we use the proxy of beam defocusing to estimate when
too much beam current is being used. As beam current increases, it becomes more and more
difficult to confine it to a sharply focused beam. For most CRT's the point at which beam
focus worsens is below the point at which phosphor damage can occur. By staying below this
point of "blooming," you avoid immediate phosphor damage.
There are other limitations of usable beam current. Heat is produced by the current
flow. Direct view CRT's use a metal mask to help direct the red, green, and blue beams to
the appropriate color phosphors. A high beam current can heat up the metal mask and warp
it. This is seen as a sudden shift in color of the screen and could indicate the danger of
permanent mask warping. Obviously you want to keep your controls below this point.
Projection CRT's are driven at much higher beam currents, so high that liquid cooling
of the phosphors is virtually required. This means that projection sets are even closer to
the physical limits of the phosphors and particular attention must be paid to never
overdriving the tubes.
Over time, phosphors age and solarize. The more light emission they are forced to
produce, particularly if near maximal output, the faster their light output drops. This is
why bright, fixed images can permanently burn themselves into a screen. By limiting beam
current to reasonable levels, you slow this process and reduce the risk to your screen.
The electrons are emitted by a heated filament, the cathode, of a CRT display. The
cathode is coated with special rare earth elements to improve electron emission. Over
time, this coating loses its effectiveness and you notice this as a blurring of the
electron beam even at low light output. The aging process causes a larger portion (other
than the tip) to become involved with emitting electrons. Since the beam spot is
essentially an image of the active region of the cathode, this increase in active region
appears as enlarged (blurred) electron beam spot size. Higher beam currents accelerate
this aging, but not to the same degree that it damages the phosphor.
Now we've gone over some reasons to keep white level down in order to protect the
display. There are also imaging quality reasons. We've already mentioned the defocusing of
the beam when current is too high. This blurs the image and reduces resolution. Also,
running too high causes the relationship of input signal to output light to be altered. If
this runs outside the "linear" range of the CRT, the relative brightness of
signal levels from black to white are distorted. You perceive this as something being
unrealistic or wrong with the contrast of a picture.
The high voltage supply used to produce the electron beam is often derived from the
horizontal deflection circuitry of the television. If beam current demands are too high,
the demand can drag down the horizontal deflection circuit. You see this as a horizontal
geometry distortion. Hence the visible bending of the left and right vertical lines on
either side of a Needle Pulses pattern in AVIA. Although not something that will damage a
set, this type of geometric distortion degrades the image. By keeping white level down,
you also avoid this problem. Some displays are designed such that this effect doesn't
occur. In these displays, you never see the vertical lines bend, however you will still
In short, white level should be set to avoid increasing the risk of permanent damage to
the display, slow aging of the phosphors & cathode, and improve image resolution,
gamma response, and geometric accuracy.
Black level, which determines the baseline upon which the video signal rides sets the
appearance of black, not how much overall light is output by the display. This needs to be
set at the lighting condition which is to be used for viewing because the correct setting
varies with ambient light. Too high a black level washes out the picture. Too low a black
level causes shadow details to be clipped and displayed as black.
Most consumer displays complicate setting of black level because they do not hold black
level constant as overall picture level changes. That is, black is displayed differently
depending on how bright the rest of the image is. This is also called imperfect DC
restoration or clamping. The solution in this case is to bias the display with a moderate
picture level image while setting black level. This allows you to arrive at a compromise
level which works for most images.
Test patterns traditionally used a blacker-than black signal to help indicate when
black level was correctly set. After all, you can't actually make the display any blacker
than black so if "black" on the display is brighter than it should be the even
darker (signal wise) BTB signal would appear be visible as a dark feature. When the BTB
and black just appear identical, the display is correctly set to make black appear black.
Many DVD players and some video processors don't pass the BTB signal so this method of
detecting when black level is correctly set doesn't always work. Also, the traditional
patterns unfortunately aligned edges of pattern features with each other leading to
optical illusions which confused viewers whether or not the BTB bar is visible. For these
reasons AVIA uses "Black Bar" patterns to indicate correct black level. These
are a pair of animated bars which move back and forth on screen. The motion makes it easy
to see if a bar is visible and helps avoid the ambiguity of optical illusions of aligned,
fixed lines. One bar is very near black, the other slightly brighter. When black level is
correct, the darker black bar is just very barely visible. If black level is too low, one
or both bars disappear. This allows one to find correct black level whether or not
equipment passes blacker than black.
The situation is different on LCD's because the usual phenomena of geometry distortion
and electron beam defocusing (blooming) don't occur with LCD's. Another limiting factor
comes into play. LCD control circuitry in LCD projectors have a relatively abrupt point
above which video signals become displayed as white. We call this "white
clipping" on AVIA. electron guns.
Basically, if you set white level too high on an LCD projector you will find that near
white details turn into white instead of something that is darker than white. Highlight
details are hidden and the image looks solarized. Finding the white level setting which
avoids white clipping is the key to maximizing LCD projector light output without
degrading image quality.
As an aside, digital domain video displays can also exhibit a similar clipping effect
when the video signal cannot be represented within the bit range of the system. You can
sometimes see this on computer monitors displaying video from a DVD-ROM.
AVIA has new moving "white bars" in its main pattern for adjusting white
level, the Needle Pulses + Log Steps pattern. You'll find a pair of near white bars which
move back and forth. If you set white level too high on a LCD projector you'll see one or
both of these white bars become white ( and disappear since you can't see white on a white
background). The maximal white level setting is found by adjusting your LCD projector to
just below the point at which the rightmost (brighter) white bar becomes white. Once that
point is found, you know the max usable white setting for your LCD projector.
The Needle Pulses + Log Steps pattern in AVIA serves as a unified tool for both CRT and
LCD display white level adjustment by combining tests for geometry distortion, blooming,
gray scale linearity, and white level clipping into a single pattern.
Once the limits for white level are found for your display. The next step is to drop
down to a white level setting which is below the max and still produces a white which
appears white rather than gray.
Black level is set the same way with AVIA on both LCD and CRT projectors.
Black Level Clamping (aka DC Restoration)
Why does the appearance of black vary with different scenes?
The appearance of "black" often varies depending on the remainder of the
image on consumer grade video displays. Another more technical term for how stable black
remains is "DC Restoration."
Let's review how the video signal is represented as an electronic signal. (Yes, I'm
ignoring phase inversions in the amplifier stages for this discussion because it would
confuse the central issue) The image information is an AC signal whose voltage level
corresponds to how bright the image should be at that moment of the image scanning
process. In American NTSC video, the luminance runs from 7.5 (black) to 100 IRE (maximal
white). Synchronization pulses are negative to -40 IRE. Notice that black is represented
by the voltage level being at 7.5 IRE rather than 0 IRE. In Japanese NTSC, black is
represented by 0 IRE. The reasons and ramifications of this difference would be an entire
As the signal passes through the video system, it requires several stages of
amplification. Each stage is coupled to the next usually via a capacitor. The capacitor
passes AC signals but not the DC offset from relative to ground to the next stage. This
means that the zero level of the signal is not actually transferred from stage to stage.
You get a signal which varies up and down in voltage but trying to tell by looking at the
final signal, you can't tell where black should be because you don't have an absolute
reference of where on the waveform is black. The appearance of black to drift up and down
with the average signal amplitude.
The above would be entirely unacceptable so the video circuits are actually designed
with various means of "clamping" the black level at a known level. This process
of "DC Restoration" is usually imperfect in consumer sets. Hence, the appearance
of black darkens and lightens depending on the average picture level. This means usually
means that black is a bit lighter during dark scenes than bright scenes. Professional
level monitors and projectors include circuits which produce nearly perfect black level
It has been argued whether or not perfect DC restoration is desirable. Some viewers
like black to be slightly lighter during darker scenes so they can better see shadow
details in difficult night scenes. Others believe this compromises the intent of the
Most of use have displays which have imperfect DC restoration. How should one deal with
the calibration of a signal who appearance varies? The solution used in both AVIA and VE
is to use calibrate black while displaying a test pattern whose average picture level is
moderate. For instance AVIA uses Black Bars with a Half Gray pattern for setting black
level. This means that black level is calibrated to a compromise which satisfies most
It is sometimes desirable to calibrate black level intentionally with a higher or lower
APL test pattern. For instance, you may have a projector which has nearly perfect black
level clamping but has some light scatter. A high APL image on such a display would tend
to obscure the appearance of black bars. In this instance you may prefer to use a low APL
black bar pattern. On the other hand, one could argue that a higher APL pattern would
compensate for the light scatter.
AVIA supplies Black Bar patterns with black background or a half white background,
color bars, and in the Needle Pulses patterns. You can follow the recommendation for most
situations, but you also have other choices. Just think about your goals in selecting a
different APL black bar pattern.
So in short, the varying appearance of black on your display is probably normal for
your display and not an indication of improper function.
Should I Set my DVD Player to Enhanced or Normal Black?
NTSC video signal levels are commonly measured in IRE units which can be converted to
voltage levels. The conversion isn't important to this discussion. IRE units are easier to
use so we all tend to refer to signal levels in IRE rather than volts.
100 IRE represents the brightest white. 7.5 IRE, rather than 0 IRE, is black due to
historical limitation in equipment. This is true in North American video equipment. In
Japan, 0 IRE is black. The offset from 0 to 7.5 IRE is referred to as "setup."
Your DVD player adds the setup to the output signal to make "black" come out at
7.5 IRE if you use normal settings.
Your player also gives you the option of making black come out of the player at 0 IRE.
This is the "enhanced" black setting. Why might you want to do that? Well,
normal NTSC video has 100-7.5 IRE or 92.5 IRE of dynamic range from black to white. By
selecting "enhanced" blacks the dynamic range is 100 IRE, a little bit larger of
a voltage swing. Is this a good thing? It depends.
Your television must be told what level IRE is black. That's essentially what you are
doing when you adjust the black level control (brightness). The AVIA test patterns include
portions which are black and very near black so you can tell what you are doing with a
known target. As long as you set the television to display black (whether it is 7.5 or 0
IRE) truly as black you're fine. This would seem to indicate that it's good to use the
enhanced black setting since black gets correctly displayed. You get a larger signal
dynamic range to avoid degradation, but there is a catch. The standard level for black for
all your other sources is 7.5 IRE, not 0 IRE.
If your display allows you to independently set black level for each video source, then
it's no problem to set the DVD video input settings to display 0 IRE as black. You'd then
calibrate the other video input settings to show 7.5 IRE as black. Unfortunately, some
displays don't let you independently set black level for each input. Getting one right
makes the others wrong.
If the display is calibrated to display 7.5 IRE as black and you view an
"enhanced" black signal, all the shadow details which between 0 and 7.5 IRE will
be lost as pure black.
If the display is calibrated to display 0 IRE as black and you view standard American
NTSC material which has black at 7.5 IRE, the picture will be somewhat washed out because
the blackest black will actually be a dark gray.
The answer depends on whether or not your display remembers separate black level
settings for each video input. If it can, then you could go ahead and use the enhanced
black setting. You'll still have to calibrate your other inputs for 7.5 IRE black. For
practical purposes, the increased dynamic range won't really make a difference because a
no matter the dynamic range, the calibrated display still displays black as the same black
and white as the same white.
Another pitfall may occur if you use video processors. Their inputs must also be
configured to recognize black at the setup level you choose at the player. If you decide
to use enhanced blacks, you need to think about how that affects the rest of your system.
Selecting normal, 7.5 IRE black means less to worry about.
Setting Speaker Level with AVIA
Let's go back and examine what is happening when setting a system to reference level.
You are attempting to set sound reproduction level such that for any given sound you
produce the same loudness as was heard in a mixing studio whose system is also set to
reference level. Maximum SPL level is 105 dB, but a reference tone recorded at maximal SPL
would be difficult to use so reference tones are usually recorded at least 20 dB softer.
In the case of AVIA's level setting tests, the encoded sound should produce a measured
level of 85 db SPL when the amplifier and speaker are set to reference levels. In a larger
room, the amount of energy needed from the amplifier would be larger but the same SPL
level of 85 dB would need to be attained. With VE, the test tone is recorded yet another
10 dB softer thus the target SPL measurement is also 10 dB softer, 75 db SPL when the
system is at reference level. Each channel needs to be adjusted to attain that signal
level for the entire system to be at reference level.
Now for the oddities. Unless your receiver is THX certified, the built in test tones
are not guaranteed to be the right level to set reference level. In higher end processors,
the built-in tones are set to the correct level such that they can be used to set
reference level, usually targeting 75 dB SPL. You have to check with the manufacturer or
manual to see what target SPL to aim for when using built-in tones. For all receivers with
built-in tones, you can use the built-in tones to balance the channels relative to each
other, but not necessarily to set absolute level to reference.
There are complications. We don't all have identical sounding speakers and room
acoustics. Some systems have large speakers and satellites. The room may absorb some
frequencies more from some speakers than others. For this reason, test tones for setting
channel level are usually not pink or white noise. Instead, a shaped noise whose spectral
distribution is centered at a frequency which most speakers can reproduce is used. That
way the effect of non-identical speakers can be partially compensated. Room effects are
more difficult to avoid. This is important when one goes from one set of test tones to
another. Although both sets are encoded at the correct levels in a perfect system, real
world speaker and acoustics can cause the measured SPL's to slightly differ. The frequency
energy distribution would have to be identical between the tones to achieve exactly the
same result. This is why your calibration can be a bit different between built-in tones
and those in AVIA or VE. Nothing is wrong with your equipment, it is an effect of
Where the master volume control ends up when you are at "reference" level
differs from model to model of receiver. Some processors let you set the master to 0 dB
(or it automatically sets master to 0 dB) and then you adjust the individual channel
levels until they each produce reference level SPL's. In such a system, 0 dB on the master
volume is reference level. On many receivers, one cannot place the master volume at the 0
dB point and still have enough range in the individual channel adjustments to achieve
reference level. On such receivers, the master volume level for reference is whatever
setting you had it at when you set your individual channels to reference. If that setting
was -12 dB, then reference level on that receiver would correspond to -12 dB on the master
A feature built into AVIA's tutorial probably adds some confusion. Listening at
reference level is very loud. In most home settings, a master volume of about 10 dB below
reference is more comfortable for listening. You'll note that the beginner's tutorial in
AVIA has you initially balance your channels at 75 dB SPL rather than 85 dB SPL. This sets
the system 10 dB below reference and automatically places you in an appropriate level for
home listening. It isn't until the next section that you learn to target 85 dB SPL to
actually be at reference level. I think it's even easier to simply calibrate all channels
to reach 85 dB SPL, then turn down the master volume to comfortable listening level, and
finally recheck channel balance. Most receivers track the channel levels correctly with
each other as one alters master volume, but you may wish to recheck individual channel SPL
levels at your usual master volume setting to double check that your receiver tracks all
the channels together as master volume is changed. If you find the individual channels are
not tracking together, you may wish to readjust the channels to make them match each other
at your normal listening level.
On occasion, you may be told that your subwoofer should be calibrated to produce an SPL
which is 10 dB higher than the other channels. There is no need to do this with AVIA's
subwoofer test tones because they are recorded 10 dB softer to automatically produce a 10
dB higher subwoofer setting when you target the same 85 dB SPL. If one wishes to be
technically more correct, the 10 dB offset actually is only true if one is using an RTA to
measure sound levels. We're using an SPL which would read about 3 dB lower for the same
subwoofer setting. If you want to be completely correct, place sub level 3 dB lower at 82
dB instead of 85 dB SPL.
Some receivers have built-in test tones and force you to listen to them during
adjustments rather than using those from a test disc. In such receivers, one can do an
initial setup with the built-in tones, then re-measure with tones from the calibration
DVD. For each channel, one would then note the amount of error in dB. Next go back and
adjust each channel the amount needed to correct the error. It may take a few rounds to
get everything right if the receiver doesn't let you use external tones.
The LFE channel level is normally already set in the receiver. On a few units you can
adjust the relative LFE level. If I recall correctly, DD has a suggested LFE offset of 0
dB, and DTS suggests a 0 dB offset for music and +10 dB for movie sound tracks.
Using AVIA Phase Tests to Fine Tune Speaker Distance
AVIA's speaker phase testing signals are also useful for very accurate adjustment of
speaker delays and distances. You'll need an analog RS SPL meter set to fast response in
order to take advantage of this tidbit. This may seem a bizarre way to check delays and
speaker distances but it is surprisingly accurate.
The phasing tests work by playing noise in the two channels being tested in phase and
180 degree out of phase intermittently. If the speaker distances and delays are both set
correctly, then the in phase sounds from both speakers reinforce each other at the prime
listening positioning. During the out of phase (diffuse) portion of the test, the sounds
cancel. An SPL meter set to fast response can readily show the magnitude of the
Start by playing the Phase left front/right front signal. Move your SPL meter slowly
left and right at your listening position. If you have set distance and delays correctly
the maximal SPL delta will occur in the middle of your sitting position. I get about a 6
dB needle bounce on my system. If it happens right of center, then your right speaker is
either too farther away than the left speaker or delayed more than the left speaker.
Conversely, if the peak SPL delta occurs left of your prime listening spot, the left
speaker is too far or excessively delayed.
Once you have the front left and right speaker distanced and delayed exactly right, the
SPL meter position at peak delta will be in the middle of your prime listening position.
Note that position carefully. You'll need to be able to refer to that point within half an
inch during the next step.
Now comes the trickery that gets the center speaker also precisely phased and delayed.
The AVIA disc also has a Phase Left Front/Center test. We can take advantage of it to
bring all three front speakers into very tight phase alignment. From the previous step we
already know where the two front main speakers are in phase. Leave the left and right
delays and speaker positions alone now. We'll next adjust the center speaker to be in
phase with the left front. This places all three into phase.
Play the Phase Left Front/Center test and once more move the SPL meter left and right
to find the maximal SPL delta point. Compare this new position to the one for the front
mains. If all is perfect, they exactly coincide. If the left/center maximal SPL delta
point is left of the left/right point, then the center speaker is either too close or
insufficiently delayed. If the left/center max delta point is right of the left/right max
delta, then the center speaker is too far. Move or adjust CENTER channel delay as needed
to get the left/center max SPL delta to occur at the exact same place as for the
Your left, center, right speakers are now in phase. You'll probably note that a 1 msec
adjustment in channel delay makes for a considerable shift in max SPL delta position.
After all, that is about a 1 foot speaker distance equivalent. Use very small speaker
movements to fine tune the center speaker into phase alignment.
Put your head at the center of the max SPL delta position and listen to some stereo and
5 channel material. You will be pleased with what has happened to sound imaging in your
Moving your speakers to achieve exact phase match isn't the entire story. One must also
position the speakers with relation to room acoustics to smooth frequency response.
Sometimes, moving speakers into exact phase also moves one or more of them into positions
that yield uneven frequency response. In such cases, some compromise is needed to address
both imaging and frequency response concerns. Happily, the home theater sound processor
does have delays and these can sometimes help bring speakers into phase, while still
keeping them closer to best tonal balance position.