If you are brave at heart and have nothing better to do, read on and I'll try to get you through it.

            Before any explanation can be attempted, a number of commonly used terms must be understood.  These are:

1. Composite Signal -- a video signal comprising all necessary information to reproduce the video picture, including all synchronizing information.

2.  Non-composite Signal -- a video signal comprising all the necessary information except sync pulses.

3. Synchronous Signal -- a signal is synchronous when all synchronizing pulses are in time coincidence with the reference signal.

4. Non-synchronous Signal -- a signal who's synchronizing pulses are not in time coincidence with the reference signal.

5. Phased Signal -- a signal is said to be Phased when its color burst is running in coincidence with that of the reference signal.

6.  Reference Signal -- in a switcher, for example, this would be the selected input against which all others would be judged.

What  Is Timing?

            This is the process of ensuring, by planning and measurement, that the various signal paths leading to a switching system are synchronous with each other upon arrival at the input.

            Timing can be subdivided into monochrome timing and color timing.  These terms really define the accuracy to which timing has to be carried out.

            Correct monochrome timing ensures that the sync pulses on the input signals to a switcher, for example, are within the following FCC tolerances:  plus/minus 50 nsecs. or plus/minus 41 ft. of coaxial cable.  This appeals to be a large variation, and in actual practice much closer tolerances are adhered to.  Any serious mistiming between consecutively switched signals would be visible as a horizontal shift on a picture monitor. 

            Before proceeding, let us examine the effect of cable length variations against time delay and color phase shift. If cable A is 10 ft. longer than cable B, then cable A signal will exhibit a delay of 12.24 nanoseconds (nsecs.) in relation to signal B.  We can see that this delay is well within the FCC: monochrome specifications, but let us now convert this delay into phase shift of the 3.58 Megahertz (MHz) sub-carrier. The time taken to shift 1 degree at 3.58 MHz is 0.77 nsecs.  We, therefore, have a phase shift of

12.24/0.77 - 15.9 degrees

which is completely unacceptable under any circumstances.  The solution is to time the color signals to a much tighter specification.  The generally accepted figure is 1.5 nsecs. or 2 degrees phase shift.

What Is Phasing?

            This is the process of ensuring that one video signal (signal A) is in phase with another video signal (signal B.)  In the NTSC system (the system used in the United States) , the color sub-carrier is 3.58 MHz and this is the frequency at which color timing and phasing are carried out.

            Phasing is used to define the adjustment of sub-carrier phase at one video source, such as a camera control unit or auxiliary, to ensure that when the video signal, from that device, arrives at the input of a switching system or other ultimate destination, that it is in phase with all the other inputs. 

            It is also used to define the timing of a system to ensure that signals traversing various paths are in phase with each other when they arrive at a combining point.

            Let us consider a system consisting of two monochrome cameras feeding a switching system, which in turn feeds a video tape recorder (VTR.)  This is a typical, small installation.  Most any video-producing device such as a VTR could be substituted for the source video and transmitter could be substituted for the destination device.

            If the video switching system is to function correctly, there must be no tearing, jumping or other visible disturbance on the monitor when cutting, mixing, or using an effects generator.  To achieve this, signals from the video sources must arrive at the same time (or be synchronous) at the input of the switcher. This means RIGHT AT THE INPUT OF THE SWITCHER, not a jackfield that may be connected to the switcher by various lengths of coaxial cable, but at the actual input connectors of the switching system.  The two cameras used in our example require synchronizing pulses, sync, blanking, vertical and horizontal drive. These are obtained from our master or station sync generator.

            The switcher also needs an input from the station sync generator for the following reasons:

1.         To ensure that a cut from video source to any other video source will occur during the vertical blanking periods, so that no visible disturbance will occur. 

2.         To provide the effects generator with a reference to produce vertical and horizontal wipes.

3.         To provide synchronizing pulses for converting non-composite inputs into composite outputs.

            To simplify the approach we will at present consider the switching system as an in/out device that possesses an internal delay.

            We must time the video signal of camera 1 to arrive at the switcher input in synchronism with that of camera 2. This is quite simple once we understand what is actually happening let us ignore camera 2 and follow the synchronizing pulses from the generator to the cameras' camera control unit (CCU) or the auxiliary of camera 1, and the video from this auxiliary to the VTR. 

            The whole process starts at time = 0 when the pulses leave the generator.  Each pulse passes through a length of coaxial cable to the input of a distribution amplifier. The distribution amplifier provides a number of outputs.  The pulses we are following each leave their respective distribution amplifiers (DA's) and then pass through a length of coaxial cable to the camera auxiliary.  This is important -- the pulse generator produces the required pulses with a fixed time relationship and it is, therefore, imperative that the path delay for each pulse be identical.  Older systems sent these pulses separately to each piece of equipment.  Sync generators now produce a signal called black burst. 

            This is a composite signal that contains all the elements of these various individual pulses in addition to color information as well.  This newer and more widely used approach eliminates many problems, but not all and timing of video signals is still required as no two video sources are located the same distance from their destination there by having different cable lengths.   

            The auxiliary uses the sync pulses to synchronize the video signal generated at the camera head and to make this signal composite.  This video signal has a fixed time relationship with the pulse generator. Other primary sources connected to this generator will have a fixed time relationship with it, and by definition, also with each other. Upon leaving the auxiliary, the video signal passes through a length of coaxial cable to reach the switching system it passes through the switching system and finally through a length of coaxial cable to the VTR.

         If the camera 2 auxiliary internal delay is the same as that of camera I, then, by making the coaxial cables (including pulses to auxiliary cables as well as auxiliary to switcher coax) for camera 2 identical in length to those for camera 1, we cause both video signals to be synchronous at the input of the switcher.

            But what happens if the CCU of camera 2 has a different internal delay to that of camera 1?   If the internal delay of camera 2 is greater then we either have to lengthen one of camera 1's cables or shorten one of camera 2's. (If the internal delay of camera 2 is less, the reverse applies.)

            Let us consider the former.  The video feed from any video source to its destination, in this case the switcher, should be kept as short as possible and, if of necessity, this is greater than 100 ft. of coaxial cable, an equalizing amplifier should be installed to correct for frequency attenuation characteristics present in all cable.

            The coaxial cables feeding pulses from the distribution amplifiers to the CCU of camera 2 are all cut to the same length.  If this were impossible for any reason, then the pulse feeds of camera 1 would have to be lengthened. To replace long lengths of cable, lumped delay units can be installed.

            Once the cameras are synchronous at the input of the switcher, we need only to time the sync feed to the switcher for the whole system timing to be complete. There is only one point in this system where two signals are present, and that is at the input of the switcher.  The VTR is fed from the output of the switcher, which if its internal timing is correct, will only act as a delay to these signals arriving at its input.

 From the preceding simple example we have learned that:

1.             Primary sources, such as cameras, possess an internal delay. This is defined as the time a video signal leaves the primary source, taking the time the synchronizing pulses arrive as zero. All primary sources do not necessarily have the same internal delay.

2.         A signal, whether it is the complete video signal or synchronizing signal, takes time to travel through coaxial cable. This time for double shielded coaxial cable such as Belden 1505A is approximately 1.2 nsecs. per ft. (1.2 micro-seconds (usecs.) per 1000 ft.)

3.         All equipment, such as amplifiers, switching systems, etc., through which the signal passes also possess internal delay.   In this case it is the time the signal leaves the equipment, taking the time it arrived at the input as zero.

4.         All systems, no matter how simple, require some planning, and it is recommended that a form of timing diagram or chart be devised.

5.            Physical locations of equipment such as CCU's, VTR's, switching equipment, pulse generator, video amplifiers, etc., must be taken into account.

6.         Long runs of video --- in excess of 100 ft. -- must be equalized.  It is, therefore, to our advantage to compensate delay variations in the synchronizing pulse feeds. There are other considerations to be taken into account. These will be explained in the final summary.

7.         The tolerance on timing for monochrome 50 nsecs. (or 33 ft. of cable). Timing is however carried out to a tolerance of 15 ft.

Note: I do recall seeing thousands of feet of cable piled on top of equipment racks at NBC in Burbank, many years ago, in their efforts to achieve timing in their plant.

Making Monochrome Timing Measurements

            It is important to know the fundamentals and those things which affect timing before considering any thing more advanced.  It is easy to forget.  This is why we are going step-by-step, presenting monochrome first to insure that your education is completely well rounded.  We will present the information about color later. 

            In monochrome timing it is not necessary to make absolute measurements what is required is an accurate method of measuring the difference in delay between two or more signals. The average operator at our station doesn't need to be able to perform this kind of measurement, but should know how it is done.  The technique and/or method is included herein as this is also the stations technical standard for maintenance as well.  It is accomplished with an oscilloscope known as a double beam oscilloscope.  Both signals are displayed first checking vertical and then horizontal pulse alignment, at the normal amplitude or "Y" setting of 0.2 V/cm.  Once this has been accomplished, the Y gain is increased to display the sync pulses only, and the X (or time scale) to show only the leading edges of the sync pulses to be compared. We can now read the difference between pulses in nanoseconds and convert to feet of coaxial cable. If the calibration of the oscilloscope is uncertain, add a measured length of cable to one of the inputs, and mark the displacement that occurs on the gradicule.

            If a number of signals are to be checked for synchronism, use one as a reference and measure all others against it. Do not forget to mark the input cables and write down each measurement. There will be pulses to the left and right of the displayed reference.  The longest path will be the farthest pulse to tile right.  The oscilloscope instruction book will provide the necessary lineup and operation.

A MORE COMPLEX MONOCHROME SYSTEM

We can now progress to a larger monochrome system namely, two studios feeding a master control with a common film camera feed.  Older television facilities were set up this way.   Newer television facilities would replace the film camera with a VTR, Still store, etc.  In this case it is essential we know where each item on the video block schematic is physically located. For example, it is impossible to keep video paths short if the two units to be connected are in widely separated parts of the building. In this situation it would be desirable to install the two studio switchers and the master control switcher in adjacent racks. Video sources should also be housed in adjacent racks.  Each of the switching systems possesses its own internal delay. If they were identical systems, they would have identical internal delays. This would, of course, simplify our timing. T1' and T2'  would now be the same. If the two switching systems did not possess the same internal delay, a delay unit could be installed in the output cable of the switching system with the shortest internal delay.  The value of this delay unit would, of course, equal the difference between the two internal delays. For significant delays in excess of 100 ft., an amplifier would be required, as shown in the film to master control path. 

            We are now in a position to make a simplified timing scale.  The numbers above each vertical line indicate the sequence used to construct the drawing.  Our first reference is the input of the two switching systems, T1 and T2.

            The second is the internal delay of these switching systems that we will make identical T1' and T2'. 

            The third is master control input.  This is determined by the length of coaxial cable required to connect the switching systems to the master control switcher. The two coaxial cables from switcher 1 and switcher 2 to the master control switcher we will make identical in length. 

            The fourth vertical takes into account the internal delay of master control. This is not essential to our timing but is put in for completeness.

            Five is the output of the camera's auxiliaries. 

            Six is the internal delay of the auxiliaries. 

            If the auxiliaries are not the same and possess different internal delays, then the solution is similar to that shown in our first example of a simple monochrome system.

            We now drop below the reference line to time master control. Lines 1 and 3 again provide our timing references.  We shall not describe the remainder which can be checked as an exercise, but when the timing scale is finished and actual times put into the distances between lines, we can read off pulse timings.  These are shown as A, B, D and E.  "A' shows that the film camera auxiliary requires pulses timed ahead of all others, and "E'' shows that master control requires its sync feed last.

            Before we describe color timing there are a few more points which should be added:

1.         Rise time:    This is the time a pulse takes to rise from 10 percent to 90 percent of its full value. 

2.         Pulse duration:              This is the time a pulse exists measured at 50 percent of its full value.

            The reason for adding these two terms is that  (1) the FCC has specifications governing their tolerances.  And  (2) that some equipment regenerates pulses. This means that when timing measurements are made, it is not unusual to see different rise times and pulse durations. It is, therefore, necessary in these cases to time leading edges of sync at the 50 percent mark.

TIMING A MONOCHROME SYSTEM WITH A CENTRAL TECHNICAL AREA

            Here is another example that should clarify the points raised in timing a monochrome system. 

            This is not the only possible layout, but it does provide short video cables.  Do not forget that a logical approach in positioning equipment is essential for easy maintenance and operation.   All numbering is left to right at the front of rack and right to left at the rear.  This may appear to he an absurd point to raise but both installation and timing must be carried out methodically. 

            Now that we have positioned our equipment racks, we tabulate all the timing information available from the manufacturer's instruction books. These figures are for the purpose of this example only: if the manufacturer did not provide sufficient data, then run a temporary feed of synchronizing pulses to the equipment and obtain the required information by measurement.  

We now transfer the figures from the table to tile diagram, adding the length of interconnecting cables. 

            Install delays indicated; switch on the equipment and when it has settled down to its operating temperature, set levels. And check frequency response, after which check timing, adjusting where necessary.

            CAUTION:             ADJUSTMENT OF FREQUENCY RESPONSE ADJUSTS DELAY

COLOR TIMING

            This is similar to monochrome timing.  In fact, monochrome timing has to be carried out to make certain that sources are synchronous before color timing starts. It is essential that a preliminary plan be devised before starting. Let us consider the system in already timed for monochrome.    What do we do to make sure it will pass color? For the purposes of this example, we shall consider the switching systems and master control color timed.  We shall consider timing a switcher for color later in this document.  We now redraw to indicate that the cameras can be color phased at their respective CCU's.   

            Let us consider this schematic for a moment. If all inputs are synchronous, what is wrong with phasing the inputs and leaving it at that?  Nothing, except in our example it is impossible to achieve.  Let us phase all sources into switcher 1. If we phase tile film camera into switcher 1, we cannot change it to correct its phase into switcher 2, or master control.  What we could do is to phase the inputs of switcher 2 to that of the film camera.  This leaves master control with no method of correcting the phase of studio 1, studio 2 or tile film camera in fact, its only adjustable input is camera 5.

   From the previous examples, we have seen that by making video cables of identical length for all inputs and adjusting the synchronizing pulse to their respective CCU's, we can make all inputs synchronous. If we now carry this out on our system, ignoring the film camera feed to master control, use short runs of video cable, and what is most important, measure the delay experienced by sub-carrier (3.58 MHz) on each cable after it has been installed.   We call trim the cables so that each signal experiences the same delay in reaching the INPUT of the switcher. If the cables are over 100 ft., then it is essential that measurements be made when the room temperature has stabilized at its normal value. For trimming cables, the delay at 3.58 is 2 degrees per foot, so that it should be possible to trim all input cables to better than 0.5 degrees (3" of coaxial cable.)

            Once this has been completed, we can phase all inputs. If our timing is correct, all inputs to both switchers will be in phase. In our example we would phase cameras 1 to 4 to the film camera, at each switcher input. We now check the phase of each switching system, arriving at the input of master control. We correct the path delay through switcher 1 to master control to be identical to that through switcher 2 to master control. We would select film to air at both switcher control panels and measure delay difference at the input of master control. and then lengthen the shortest delay.

            We now correct the delay of the film camera cable (film camera DA to master control so the film camera is in phase with switcher 1 and 2 at the input of master control.

            On completion, phase in camera 5 to master control. If we have planned correctly and the switching systems and master control are close together, it should he possible to hold the path delays between switchers and master control for a long period. 

            If it were impossible to locate all the switching equipment in one small area, some method of adjusting phase would have to he installed in each studio feed to master control.

MAKING COLOR TIMING MEASUREMENTS

We will require a test instrument that can measure to within plus or minus 0.77 nsecs. (1 degree at 3.58 MHz). The only equipment available at most stations which is capable of this accuracy is the Vectorscope. There are many different models and makes on the market today. 

            In addition to the signals to be measured, the Vectorscope requires a reference feed of station synchronizing pulses and sub-carrier.  It is essential that the signals to be measured contain the 3.58 MHz sub-carrier and burst!   It is also essential those all-level settings: frequency response adjustments, etc., have been carried out prior to timing measurements.   (Don't forget that 226 ft. of coaxial cable is 360 degrees at 3.58 MHz.)  The type of coax is extremely important in this matter.

            The simplest way of measuring the relative delay of signals arriving at a combining point, such as the input to a switching system, is to connect a signal to the A input and adjust its burst to be fully extended along the center Y axis.

NOTE:             This is accomplished by using the "A" gain control and the "A" phase adjustment control.  If the Vectorscope possesses a direct readout adjustment of the phase, set this to zero before adjusting the variable control.   Now replace this signal with each of the remaining signals in turn and read the circular graticule (each major division is 10 degrees and each sub-division 2 degrees with the reference point in the center of the circle).

23.  Video Distortion.

A.  Linear Distortion .  There are four types of Linear Distortions seen in video:

1. Short time, 2. Line time, 3. Field time and 4. Long time.

1.         Sort time distortions occur in some time period less than the horizontal sync (63.5uS) and generally affect horizontal sharpness and definition of the picture. Ringing, Overshoot, and Undershoot are examples of short time distortions, and they indicate problems with the high frequency response of the video device under test.)

2.         Line Time Distortion Example: Line Time distortions have a time period smaller than that of the horizontal sync (63.5uS) and show up as smearing or streaking in the picture from left to right, over the entire height of the picture. This usually indicates a problem with the DC or AC coupling of the video amplifier of the video device under test.

3.         Field Time Distortion Example: Field Time distortions have a time period close to the vertical sync rate (60Hz) and indicate problems in the low frequency response of the video equipment under test. This type of problem shows up as a vertical shading from top to bottom, or sometimes a "flag waving" near the top of the picture.

4.         Long Time Distortion Example: Long time distortions are DC or extremely low frequency (less than 60Hz) and cause abrupt changes or slow rolling variations in the brightness of the entire picture. Hum bars of 60Hz AC line noise are a typical long time distortion

B.  Non Linear Distortions.  Non-Linear video Distortions are divided into three basic types:

1.  Luminance Distortions, 2.  Differential Gain Errors, and 3.  Differential Phase Errors.

1.  Luminance Distortion Example: Luminance Distortions occur when the gain or response of a video circuit changes with the amplitude of the signal. This may show up as the inability of the device under test to resolve small details that are near 100IRE amplitude while it properly resolves details that are lower in amplitude. A  5 step or 10 step staircase pattern is typically used to test for this distortion.

2.  Differential Gain Error Example: Differential Gain errors manifest themselves as the inability of the video device under test to amplify or reproduce the chrominance portion of the signal in a linear exactly matching changes in the amplitude of the video signal. This may show up as low color saturation in picture elements that are near 100IRE in amplitude. This error is also known as "differential chroma gain error."  A "modulated stairstep" pattern is often used to test for this error.

3.  Differential Phase Error Example: Differential Phase error causes the phase (hue) of the chroma signal to change with the amplitude of the luminance signal. This may show up as a color hue shift between identical colors that have different luminance values. A "modulated ramp" pattern is often used to test for this type of error.

24.  Test signals, Waveforms, & Patterns

(Used for video troubleshooting, test, and measurements.)

75.75 Color Bars -- (also known as 75% reduced amplitude bars with a 75% white reference) is a full field color bars test signal composed of a 75% gray bar (75% amplitude, 100% saturation) and 75% color bars (yellow, cyan, green, magenta, red, blue, and black).

Usage:  Color bars are by far the most widely known video test signal.  Color bars are often used to test video levels and chrominance relationships.  For example, 100.75 Color Bars is a useful signal to help measure the insertion gain of a device under test.  Insertion gain is a measure of the ability to preserve signal amplitudes through a device under test.  Errors in insertion gain are visible in the video picture as areas that are too dark or too light.   Full field color bars are used in making subjective evaluations and adjustments on color monitors.  The waveform view of the black and white bars can also be used as a reference to match the video levels of other video systems equipment.  Note that for NTSC transmission applications, chrominance amplitudes for 100% bars can cause distortions and violate NTSC transmission standards, hence the use of 75% bars.  Full field color bars are also often recorded at the head (leader) of a videotape and monitored during playback.

100.75 Color Bars -- Usage Summary:  Insertion Gain, Monitor Alignment, Video Levels (WFM), Chroma Level and Phase100.75 Color Bars (also known as 75% bars reduced amplitude bars with a 100% white reference) is a full field color bars test signal composed of a 100% white bar (100% amplitude, 100% saturation) and 75% color bars (yellow, cyan, green, magenta, red, blue, and black).

Usage:  Color bars are by far the most widely known video test signal.  Color bars are often used to test video levels and chrominance relationships.  100.75 Color Bars are a useful signal to help measure the insertion gain of a device under test.  Insertion gain is a measure of the ability to preserve signal amplitudes through a device under test.  Errors in insertion gain are visible in the video picture as areas that are too dark or too light.   Full field color bars are used in making subjective evaluations and adjustments on color monitors.  The waveform view of the black and white bars can also be used as a reference to match the video levels of other video systems equipment.  Note that for NTSC transmission applications, chrominance amplitudes for 100% bars can cause distortions and violate NTSC transmission standards, hence the use of 75% bars.  Full field color bars are also often recorded at the head (leader) of a videotape and monitored during playback. 

100.100 Color Bars -- 100.100 Color Bars, Usage Summary:  Insertion Gain, Monitor Alignment, Video Levels (WFM), Chroma Level and Phase.  100.100 Color Bars, also known as 100% full amplitude bars, is a full field color bars test signal composed of a 100% white bar (100% amplitude, 100% saturation) and 100% color bars (yellow, cyan, green, magenta, red, blue, and black).

Usage:  Color bars are by far the most widely known video test signal.  Color bars are often used to test video levels and chrominance relationships. Insertion gain is a measure of the ability to preserve signal amplitudes through a device under test. Errors in insertion gain are visible in the video picture as areas that are too dark or too light. Full field color bars are used in making subjective evaluations and adjustments on color monitors. The waveform view of the black and white bars can also be used as a reference to match the video levels of other video systems equipment.  Note that for NTSC transmission applications, chrominance amplitudes for 100% bars can cause distortions and violate NTSC transmission standards, hence the use of 75% bars.  Full field color bars are also often recorded at the head (leader) of a videotape and monitored during playback.

Convergence -- Usage Summary:  Monitor Alignment, Linearity.  Convergence is a regular pattern of white dots and crossed lines with a black background.

Usage:  The Convergence test pattern is primarily used for alignment of video monitors to ensure that the red, green and blue electron beams in the tube all illuminate the same location (dot) on the tube's phosphors.   If the monitor is not properly aligned, then the lines of the convergence pattern may possess color ghosts or even separate into individual red, green and blue lines or dots, especially near the corners of the monitor.  The convergence pattern's regular pattern of white boxes can be used visually detect linearity problems. 

EIA Color Bars -- Usage Summary:  Insertion Gain, Monitor Alignment, Video Levels, Chroma Level and Phase.  Established by the Electronic Industries Association in their EIA RS-189A specification,  EIA Color Bars (also known as "split-field" color bars) is a standard test signal with full field color bars (75% amplitude, 100% saturation, Gray (75% white), Yellow, Cyan, Green, Magenta, Red, Blue, and Black) in the upper three-fourths of the display and additional test signals added to the lower fourth.  These additional signals include the -I signal, White Flag, +Q signal, and Black and are specifically designed to aid in television transmitter alignment. 

Usage:  The EIA Color Bar test signal is used in making phase and gain adjustments in color monitors and also used in verifying the accuracy of NTSC encoders and decoders.  The luminance component of the test signal offers a convenient gray-scale display that assists in setting color balancing and tracking on color monitors.  In transmission applications, the test signal is used for checking transmission levels and detecting the presence of differential gain and differential phase.

SMPTE Color Bars -- Usage Summary:  Insertion Gain, Monitor Alignment, Video Levels, Chroma Level and Phase)  SMPTE Color Bars is a standard test signal designed to include all the items required to setup, calibrate, and maintain a color monitor.  These items include:- standard 75% color bars signal comprising the top two-thirds of the display (similar to full-field color bars but without a black bar and with the first bar at 77 IRE instead of 100 IRE)- reverse patches of bars below the color bars, from left to right (Blue, Magenta, Cyan, and Gray)- an -I signal, a 100% white flag (100 IRE), a +Q signal, and a Pluge pattern at the bottom. The Pluge pattern consists of 3 dark gray strips from left to right, valued at 3.5 IRE, 7.5 IRE, and 11.5 IRE, respectively).

Usage:  The color bars portion of the SMPTE test signal is used in applications similar to full field color bars (often used to test video levels and chrominance relationships).  Note that the Gray, Cyan, Magenta, and Blue bars all contain an equal blue level content.  When setting up a color monitor, contrast and brightness adjustments should always be performed prior to adjusting any color controls. The Pluge pattern is designed as a helpful aid in visually establishing the black level (brightness control) of the monitor.   To perform this adjustment, increase the brightness level on the monitor until all the Pluge patterns are just visible.  Then adjust the white level (contrast or picture control) of the monitor so that the Pluge pattern looks like a linear ramp (from left to right with each step about twice a bright as the previous step).  Then, adjust the brightness level back down so that the two left-most pluge patterns merge in brightness level.  The brightness level is correctly set when the two left Pluge patterns disappear into the background and the right pattern is just barely visible. Essentially, your eye should be able to distinguish the difference between the last two Pluge strips, but not perceive any difference between the first two. The reverse color patches are positioned directly below the color bars and are used in conjunction with the chroma and hue (tint) controls on color monitors.   When the chroma and hue controls are properly adjusted the level of blue content in the bar and color patch below it will be equal matched.  These patches are in reverse sequence to the bars to aid in the visual comparison.  To perform the procedure, you first need to choose a SMPTE Color Bars with a Blue Filter test signal, or turn off the red and green guns to your color monitor, or choose the Blue-Only mode of your color monitor, if applicable.  Then adjust the color (chroma gain) control on the monitor so that the two outer vertical bar/patches match in level.  Then adjust the hue/tint (chroma phase) control on the monitor so that the inner two vertical bar/patches match in level.  The I and Q are the color signals of the R-Y and B-Y components used in encoding R, G, and B signals into NTSC video and are used in checking their phase relationships to the other colors when setting up video signals.   The 100 % (100 IRE) white flag is a convenient reference in setting video levels and white level. 

Modulated Ramp -- Usage Summary:  Nonlinear Distortions, Differential Gain, Differential Phase

Modulated Ramp is a smooth voltage ramp from 7.5 IRE to 100 IRE, upon which are a 40 IRE subcarrier of 0 degrees phase angle is superimposed.   This modulation is of the same hue and phase as the reference burst.

Usage:  The Modulated Ramp test pattern is generally used to detect differential gain (saturation) and differential phase (hue) errors.  Such errors arise when a device under test's processed output depends on the luminance levels (brightness).   When differential gain is present, colors will change in saturation as the picture brightness changes.  When differential phase is present, colors will change in hue as the picture brightness changes.

Modulated Staircase -- Usage Summary:  Nonlinear Distortions (Differential Gain, Differential Phase, Luminance Nonlinearity  Error.  The luminance-only version of the Staircase test pattern is identical to the grey-scale 5 Step pattern (see 5 Step).  The modulated Staircase test pattern consists of burst plus a 40 IRE (286 mV) peak-to-peak subcarrier modulated onto each step of the Staircase luminance signal.  The luminance-only version of the Staircase test pattern is also known as a Medium 50% Average Picture Level (APL) test signal since it has the 5 Step luminance staircase on each of the active video lines.

Usage:  The Modulated Staircase test pattern is useful for differential phase and differential gain measurements (see Modulated Ramp test pattern for further details). The luminance-only Staircase test pattern is used for nonlinearly measurements (see 5 Step pattern for further details).

Multiburst -- Usage Summary:  Video Levels, Frequency Response.  Multiburst consists of a 70 IRE bar followed by a 10 IRE bar followed by 6 frequency packets of 500 kHz, 1.0 MHz, 2.0 MHz, 3.0 MHz, 3.58 MHz, and 4.2 MHz positioned along the video line, each at 60 IRE peak-to-peak amplitude.  The fifth packet (3.58 MHz) is equal to the color subcarrier frequency. 

Usage:  The Multiburst test pattern consists of 2 bars and 6 different frequency packets along the line of video and is often used for frequency response testing.  The idea is to look at the device under test's frequency response by comparing the relative amplitude of each of the Multiburst frequency bursts with respect to one another.  An ideal device under test will output all the multiburst frequencies at the same peak-to-peak amplitude.  Typical errors in frequency response will manifest as amplitude variations in the individual packets.  The common types of errors include:          

- loss of fine details in luminance (due to high-frequency rolloff i.e. the higher frequency packets are of smaller and smaller amplitude peak-to-peak)

- noisy edges and sparkles in video pictures (due to high-frequency peaking i.e. the higher frequency packets are of larger and larger amplitude peak-to-peak)

When testing a videotape recorder, it may be necessary to use a reduced amplitude (60 IRE) Multiburst signal otherwise the high multiburst frequencies may interfere with the FM recording circuits of the videotape recorder.

Multipulse -- Usage Summary:  Group Delay, Chrominance-to-Luminance Gain, Chrominance-to-Luminance Delay.  The Multipulse test signal consists of a series of short modulated pulses of varying duration, subcarrier frequency, and amplitude, specifically: 

- a white flag bar (100 IRE bar signal of duration 5.9 microseconds)

- the 2T pulse (2T luminance-only pulse of amplitude 100 IRE , where T =125 nanoseconds), and

- a 25T modulated pulse (25T sine-squared pulse of amplitude 100 IRE, with 1.0MHz             modulation, where T = 125 nanoseconds), and

-  four 12.5T modulated pulses (12.5T sine-squared pulses of amplitude 100 IRE  with 2.0, 3.0, 3.58, and 4.2 MHz modulation, respectively, where T = 125 nanoseconds).

These signal components are supported with standard synchronizing and blanking signals.  The signal is specified in the ANSI T1.502-1988 Standard for Telecommunications.

Usage:  The Multipulse test signal is often used in broadcast transmission application since it helps identify group delay errors over the standard video passband.  Multipulse can serve as a VITS signal as well.  The exact usage of this test signal is completely described in the ANSI standard ANSI T1.502-1988.

Pulse and Bar -- Usage Summary:  K-Factor, Y/C Delay, Low Frequency Response, Chrominance-to-Luminance Gain.  The Pulse and Bar test signal consists of three basic parts:- the 12.5T modulated pulse (12.5T sine-squared pulse of amplitude 50 IRE = 357.14 mV, with 3.58MHz modulation, where T = 125 nanoseconds)- the 2T pulse (2T luminance-only pulse of amplitude 100 IRE = 714.29mV, where T =125 nanoseconds)- the white bar signal (100IRE bar signal of duration 24.6 microseconds with an inverted  2T pulse in the center of the bar).

Usage:  The 12.5T pulse portion of the Pulse and Bar test pattern can be used to detect chrominance-to-luminance gain as well as Y/C delay distortions of a device under test.  Under ideal conditions, a device under test with zero Y/C delay and no chrominance-to-luminance gain will pass the 12.5T pulse with no distortions (i.e. the bottom baseline of the pulse will be flat).  If a small peak appears on the bottom baseline of the 12.5T pulse, then only chrominance-to-luminance gain distortion is present (positive peak = low chrominance, negative peak = high chrominance).  If two symmetrical positive/negative peaks appear on the bottom baseline of the 12.5T pulse, then only Y/C delay is present.  If two asymmetrical positive/negative peaks appear on the bottom baseline of the 12.5T pulse, then both chrominance-to-luminance gain distortion and Y/C delay errors are present.  The 2T-pulse portion of the Pulse and Bar signal can be used to measure the K-Factor, a measure of linear distortion used in assessing picture quality.  The white bar portion of the signal is used in detecting distortions at low frequencies.  If the bar experiences a tilt after it is processes by the device under test, then low frequency distortions are present.  If the bar remains flat, then no low frequency distortions are present.

NTC 7 Composite -- Chrominance-to-Luminance Delay, Luminance Nonlinearly, Differential Gain/Phase.  The NTC 7 Composite test pattern consists of a line bar (125-nanosecond rise and fall time), a 2T pulse (250-nanosecond, half-amplitude duration), a 12.5T chrominance pulse (1.5625-microsecond half-amplitude duration), and a modulated 5-step staircase signal.  These signal components are supported with standard synchronizing and blanking signals.  The signal is specified in the ANSI T1.502-1988 Standard for Telecommunications.  NTC is an acronym for the Network Transmission Committee.

Usage:   The NTC 7 Composite signal is primarily used in studio and distribution testing situations.  Because it's rise time is too fast, it is not a suitable VITS signal for broadcast transmission usage (Note:  the FCC Composite test signal was designed to be used as a VITS since it's rise time is slower). The exact usage is completely specified in the ANSI standard ANSI T1.502-1988.  The line-bar portion of NTC 7 Composite is often used in detecting short time and line-time waveform distortions in transmission service testing.  The 5-step modulated staircase is often used for measuring luminance nonlinearly, differential gain and differential phase errors.

NTC 7 Combination -- NTC7 Combination, Usage Summary:  Frequency Response, Nonlinear Distortions.  NTC 7 Combination consists of a white flag, multiburst, and a 3-level modulated pedestal chrominance signal.  These signal components are supported with standard synchronizing and blanking signals. The test signal is specified in the ANSI T1.502-1988 Standard for Telecommunications.  NTC is an acronym for the Network Transmission Committee.  The white flag portion consists of an 18 microsecond, 100 IRE bar.  The multiburst portion consists of 6 standard multiburst frequency packets (500 kHz, 1.0 MHz, 2.0 MHz, 3.0 MHz, 3.58 MHz, and 4.2 MHz) positioned along the video line, each at 50 IRE peak-to-peak amplitude. The modulated pedestal portion consists of 3 chrominance packets with the same phase, centered about 0 IRE luminance level, with different amplitudes (20, 40 and 80 IRE).

Usage:  The NTC 7 Combination test pattern is designed for distribution and broadcast transmission system testing.  The exact usage of this test signal is completely described in the ANSI standard ANSI T1.502-1988.  The multiburst portion is often used in measuring amplitude response versus frequency.  The 3-level chrominance portion is used to detect chrominance-to-luminance intermodulation, chrominance nonlinear gain distortion, and chrominance nonlinear phase distortion.

NTC 7 Combination consists of a white flag, multiburst, and a 3-level modulated pedestal chrominance signal.  These signal components are supported with standard synchronizing and blanking signals. The test signal is specified in the ANSI T1.502-1988 Standard for Telecommunications.  NTC is an acronym for the Network Transmission Committee.  The white flag portion consists of an 18 microsecond, 100 IRE bar.  The multiburst portion consists of 6 standard multiburst frequency packets (500 kHz, 1.0 MHz, 2.0 MHz, 3.0 MHz, 3.58 MHz, and 4.2 MHz) positioned along the video line, each at 50 IRE peak-to-peak amplitude. The modulated pedestal portion consists of 3 chrominance packets with the same phase, centered about 0 IRE luminance level, with different amplitudes (20, 40 and 80 IRE).  Usage:  The NTC 7 Combination test pattern is designed for distribution and broadcast transmission system testing.  The exact usage of this test signal is completely described in the ANSI standard ANSI T1.502-1988.  The multiburst portion is often used in measuring amplitude response versus frequency.  The 3-level chrominance portion is used to detect chrominance-to-luminance intermodulation, chrominance nonlinear gain distortion, and chrominance nonlinear phase distortion.)

Window -- Window,  Usage Summary:  Linear Distortions, Video Levels, Frequency Response. 

The Window is a simple, uniform white rectangle in the center of a black background, designed so that the maximum amount of energy is spread in the lower portion of the video passband. The rectangle is a 100 IRE (714 mV) amplitude signal of 26 microsecond duration (about 1/2 the active picture height and width). The rise time from black to white is approximately 150 nanoseconds.  The Window pattern occurs on lines 82-200 of field 1 and lines 81-200 of field 2.

Usage:  The Window test pattern can be used for checking low-frequency distortions (ringing, smearing, streaking) and for frequency response measurements.  It can be used for simple video level checks as well.

5 Step Luminance Ramp -- Usage Summary: Nonlinear Distortion (Luminance Nonlinearly Error).  5 Step is a grey-scale luminance test signal composed of 5 grey-bar steps starting at 0 mV (0 IRE) and increasing to the right in equal steps of 143 mV (20 IRE).  It is similar to the luminance signal of the Staircase test pattern as well as the unmodulated 5-step portion of the NTC 7 Composite test pattern.

Usage:  The 5 Step test pattern is used to help detect if a device under test can process luminance consistently across the entire range of amplitudes.  Typical luminance nonlinear distortions will result in a loss of grey-scale distinctions, which means that detail is lost. To calculate nonlinear luminance error, input the 5-step test pattern into the device under test and then monitor the device under test's output on a waveform monitor

Then, measure the following:       

-    V1 = Amplitude Step (IRE) of 1st step         

-    V2 = Amplitude Step (IRE) of 5th step

Then, the luminance nonlinearly error, expressed as a % of the largest step is computed as:      

            -   % Error =  100*(V2-V1)/V2

10 Step Luminance Ramp -- Usage Summary:  Nonlinear Distortion (Luminance Nonlinearly Error)

10 Step is a grey-scale luminance test signal composed of 10 grey-bar steps starting at 0 mV (0 IRE) and increasing to the right in equal steps of 71 mV (10 IRE).  It is similar to the luminance signal of the Staircase test pattern as well as the unmodulated 5-step portion of the NTC 7 Composite test pattern.

Usage:  The 10 Step test pattern is used to help detect if a device under test can process luminance consistently across the entire range of amplitudes.  Typical luminance nonlinear distortions will result in a loss of grey-scale distinctions, which means that detail is lost. To calculate nonlinear luminance error, input the10-step test pattern into the device under test and then monitor the device under test's output on a waveform monitor

Then, measure the following:       

-    V1 = Amplitude Step (IRE) of 1st step         

-    V2 = Amplitude Step (IRE) of 10th step

Then, the luminance nonlinearly error, expressed as a % of the largest step is computed as:      

            -   % Error =  100*(V2-V1)/V2

Red Field -- Usage Summary:  General Usage, Chrominance Signal to Noise.  The Red Field (also known as Red Purity) is essentially composed of a full raster of red with the same specifications as the red bar found from the SMPTE Color Bars test signal.  Red Field provides:- Chrominance Amplitude=  626.66 mV peak-to-peak (-313.33 to 313.33 mV)- Chrominance Phase=  103.5 degrees- Luminance Pedestal=  201.74 mV

Usage:  The full-field color test patterns (Red, Blue and Green Field) are handy diagnostic test signals to help assess the ability of a device under test (such as a color monitor) to handle the individual primary color video signal components.  Often the Red, Green, and Blue test signals are displayed on a monitor while adjustments are made to the yoke magnets of the monitor's tube to ensure proper display.  The Red Field signal is often used to help visually detect the presence of noise introduced by a monitor.  Our eyes are extremely sensitive to the presence of such noise on a red field.

Green Field -- Usage Summary:  General Usage, Chrominance Signal to Noise.  The Green Field (also known as Green Purity) is essentially composed of a full raster of green with the same specifications as the green bar found from the SMPTE Color Bars test signal.  Green Field provides:- Chrominance Amplitude=  585.28 mV peak-to-peak (-292.64 to 292.64 mV)- Chrominance Phase=  240.7 degrees- Luminance Pedestal=  344.45 mV

Usage:  The full field color test patterns (Red, Blue and Green Field) are handy diagnostic test signals to help assess the ability of a device under test (such as a color monitor) to handle the individual primary color video signal components.  Often the Red, Green, and Blue test signals are displayed on a monitor while adjustments are made to the yoke magnets of the monitor's tube to ensure proper display.  The Red Field signal is often used to help visually detect the presence of noise introduced by a monitor.  Our eyes are extremely sensitive to the presence of such noise on a red field.

Blue Field -- Usage Summary:  General Usage, Chrominance Signal to Noise.  The Blue Field (also known as Blue Purity) is essentially composed of a full raster of blue with the same specifications as the blue bar found from the SMPTE Color Bars test signal.  Blue Field provides:- Chrominance Amplitude=  443.76 mV peak-to-peak (-221.88 to 221.88 mV)- Chrominance Phase=  347.1 degrees- Luminance Pedestal= 110.06 mV

Usage:  The full-field color test patterns (Red, Blue and Green Field) are handy diagnostic test signals to help assess the ability of a device under test (such as a color monitor) to handle the individual primary color video signal components.  Often the Red, Green, and Blue test signals are displayed on a monitor while adjustments are made to the yoke magnets of the monitor's tube to ensure proper display.  The Red Field signal is often used to help visually detect the presence of noise introduced by a monitor.  Our eyes are extremely sensitive to the presence of such noise on a red field.

Blackburst Field -- Usage Summary:  Synchronization Timing, Luminance Signal to Noise.

The Blackburst Field is a full black raster field of video whose level is at 53.57mv = 7.5 IRE.  It contains horizontal and vertical sync as well as a standard NTSC color burst packet reference.

Usage:   Blackburst is often used to help time and synchronize various parts of a video system and is also used in video noise measurements.

50% Luminance Field -- Usage Summary:  General Usage, Video Levels.  The 50% Field  (also known as Gray Field, or 50% Pedestal) is a full gray raster field of video whose level is at 357.14 mV = 50 IRE.

Usage:  The full-field test patterns without any chrominance content (50%, and 100% Field) are handy diagnostic test signals to help assess the ability of a device under test to pass different video levels.  Often these test signals are used in conjunction with digital storage oscilloscopes to help identify distortions that may occur over longer time periods.

100% Luminance Field -- Usage Summary:  General Usage, Video Levels).  The 100% Field (also known as White Field, or 100% Pedestal)  is a full white raster field of video whose level is at 714.29 mV = 100 IRE.

Usage:  The full-field test patterns without any chrominance content (50%, and 100% Field) are handy diagnostic test signals to help assess the ability of a device under test to pass different video levels.  Often these test signals are used in conjunction with digital storage oscilloscopes to help identify distortions that may occur over longer time periods.

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25.    Additional material will be added to these standards from time to time as needed.

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