Composite video signal with audio

A method for inserting an audio signal (132) into a composite video signal (10) having a front porch (24), a back porch (26 or 32), a horizontal sync pulse (20) with a leading edge (22), and a luminance portion (16) to provide an audio-on-video signal (222), includes removing one or more video parts (180, 200) at least partially from the luminance portion (16), sampling one or more audio parts (182, 202), biasing a zero magnitude (238) of the audio parts (182, 202) to the midpoint (240) of the maximum luminance magnitude (242), and placing the sampled parts (182, 202) at least partially within the luminance portion (16) of the composite video signal (10) to form the audio-on-video signal (222). The method for inserting also includes inserting audio parts (212) into blanking parts (206) that follow leading and trailing equalizing pulses (46, 56); and the method for inserting further includes inserting audio parts ( 214) into blanking portions (60) of test signals (58) that follow the trailing equalizing pulses (56). A method for separating an audio signal (132) from the audio-on-video signal (222) includes sampling an audio plus magnitude (230) of the audio parts (182 and/or 202) at least partially within the luminance portion (16), subtracting a bias magnitude (234) to provide an audio sample magnitude (280 or 288), holding the audio ample magnitude (280 or 288), replacing the held audio sample magnitude (20 or 288) with a successive audio sample magnitude (280 or 288) to provide a stepped audio output (320), low pass filtering (310) to smooth the stepped audio output (320) and to prevent Nyquist problems, and high pass filtering (310) to prevent noise when an audio sample magnitude (318) is held during a vertical sync pulse (48).

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to transmitting and receiving video 
and audio signals. More particularly, the present invention relates to 
apparatus and method for combining audio signals into the luminance 
portion, and into other portions, of composite video signals to provide 
audio-on-video composite signals, and for separating the audio from the 
audio-on-video composite signals. 
2. Description of the Related Art 
Video is commonly transmitted by combining various synchronizing signals, 
or timing signals, with a luminance signal to make a composite video 
signal, either amplitude or frequency modulating the r.f. carrier, and 
broadcasting the r.f. carrier with audio on frequency modulated sidebands. 
Each composite video signal includes first and second video fields of 
horizontal lines, with the first and second video fields interlaced. Each 
of the first and second video fields include a horizontal composite signal 
and a vertical blanking portion; and each horizontal composite signal 
includes a luminance portion and a horizontal blanking portion. 
The horizontal blanking portion includes a front porch, a horizontal sync 
pulse with a leading edge, and a back porch. When color video is 
broadcast, a color burst is included in the back porch of each horizontal 
composite signal. 
A plurality of horizontal composite signals is followed by a vertical 
blanking portion in which synchronizing and timing signals are placed to 
alternately produce first and second video fields of horizontal lines. The 
vertical blanking portions include leading equalizing pulses, a serrated 
vertical sync pulse, trailing equalizing pulses, and a plurality of test 
signals. 
This prior art method of broadcasting video and audio has been very 
successful; but placing audio onto sidebands results in wide bandwidth 
requirements. For instance, if color video and audio are transmitted with 
the video on sidebands in a band that includes frequencies from 1850 to 
1990 megahertz, and which is commonly called the 1900 megahertz band, and 
if both the video and audio are frequency modulated, the bandwidth 
requirement can exceed 25 megahertz. Or, of black and white video is 
transmitted with audio on sidebands, the bandwidth requirement is in the 
15-18 megahertz range. 
Further, while many bands have been available for entertainment video, 
there have been no bands available for business video. However, bands are 
now available that could be used for business video; but they are too 
narrow for conventional FM video transmission. Some of these bands are 
only 10 megahertz wide; and some are even narrower, being only 5 megahertz 
wide. 
Thus, radio frequencies are available for use by businesses; and these 
bands could be used by a bank, or other business, for communicating by 
video with branches; but using prior art techniques results in a bandwidth 
requirement in excess of 25 megahertz for color and 15-18 megahertz for 
black and white video. In contrast to bandwidth requirements for video, 
the new bands are only 5 and 10 megahertz wide. 
One solution to the requirement for a large bandwidth is to place the audio 
signal, or audio signals, onto the horizontal composite signal. Various 
schemes have been proposed to accomplish this. 
Kelly, in U.S. Pat. No. 3,423,520, issued Jan. 21, 1969, places the audio 
signal in the horizontal blanking portion, and more particularly on the 
front porch. While Kelly teaches pulse amplitude modulation, he states 
that any form of pulse modulation may be used for the audio, including 
pulse duration modulation, pulse position modulation, or pulse code 
modulation. 
Hodge, in U.S. Pat. No. 3,446,914, issued May 27, 1969, also teaches 
placing the audio signal in the horizontal blanking portion, but he 
teaches placing it on the back porch. More particularly, Hodge teaches a 
method for recording both audio and video by the use of a phase modulated 
pulse that is placed on the back porch. 
Steudel, in U.S. Pat. No. 4,156,253, issued May 22, 1979, also teaches 
placing the sound signals onto the back porch. However, Steudel teaches 
placing the sound signals, in digital form, partially before the color 
burst and partially after the color burst. 
Sugihara, in U.S. Pat. No. 4,233,627, issued Nov. 11, 1980, teaches the use 
of pulse code modulation to place audio signals into the vertical blanking 
portion. More particularly, Sugihara places the audio signals into the 
blanking parts that follow the equalizing pulses. 
Kergosien et al., in U.S. Pat. No. 4,253,115, issued Feb. 24, 1981, teach 
placing audio signals in the vertical blanking portion in digital form. 
More particularly, Kergosien et al. teach transmission of an audio 
frequency analog signal during the line synchronization interval of a 
television signal, including coding and decoding of analog values that 
have ben changed to digital form. 
Quan et al., in U.S. Pat. No. 4,333,108, issued Jun. 1, 1982, place the 
audio, in digital form, in the horizontal blanking portion. More 
particularly, the audio signal is pulse width modulated, thereby varying 
the time of at least one edge of a pulse as a function of the voltage 
level of the audio signal at a selected time. 
Katsfey, in U.S. Pat. No. 4,361,852, issued Nov. 30, 1982, teaches placing 
the audio in the vertical blanking portion. The audio signal is 
time-compressed for injection into the vertical blanking portion. When 
decoded, the audio information is read into a memory device at high speed, 
and then read out of the memory device at low speed, thereby 
reconstructing a substantially continuous audio signal. 
Shiral et al., in U.S. Pat. No. 4,442,461, issued Apr. 10, 1984, teach 
placing the audio signals on the back porch of the horizontal blanking 
portion in pulse-code-modulated form. In order to fit a sufficient number 
of digital bits onto the back porch, the back porch is extended by 
replacing the standard horizontal sync pulses with narrow pulses, so that 
the following back porch is correspondingly extended. 
Hirashima, in U.S. Pat. No. 4,745,467, issued May 17, 1988, teaches placing 
digitized delta-encoded sound signal information in the horizontal sync 
part of the horizontal blanking portion, and placing a standard digital 
signal of the same sound signal in the vertical blanking portion. 
McKenzie, in U.S. Pat. No. 4,983,967, issued Jan. 8, 1991, teaches time 
compressing the audio signal, and placing the time-compressed audio 
signal, in analog form, into the vertical blanking portion. 
While all of these prior art patents achieve the objective of placing the 
audio onto the horizontal composite signal, none of them achieve the 
simplicity and the low cost that is achieved by the present invention. 
SUMMARY OF THE INVENTION 
In the present invention, video transmitter apparatus removes a video part 
of the luminance portion of a horizontal composite signal, and replaces 
this video part with an audio sample. The audio part is biased up to a 
midpoint of a luminance magnitude, so that both positive and negative 
magnitudes of the audio signal will stay between the horizontal blanking 
magnitude and the maximum luminance magnitude. 
Preferably the audio sample, which is timed from the leading edge of the 
horizontal sync pulse, is placed into the luminance portion proximal to 
the back porch. Optionally, the audio sample is placed near the front 
porch. Or, if desired, two audio, or other nonvideo samples, may be placed 
into the luminance portion, one near each porch. 
When color video is broadcast, the color burst consumes most of the time 
duration of the back porch, so that there is very little space to place 
time signals on the back porch. In contrast, in the present invention, 
audio samples of relatively long time duration, such as 3 microseconds, 
are placed into the luminance portion. 
In addition, to placing at least one audio sample into the luminance 
portion, or at least partially within the luminance portion, the present 
invention places a plurality of audio samples in the vertical blanking 
portion. Preferably, one audio sample is placed into three different 
portions of the vertical blanking portion. 
More particularly, in a preferred embodiment one audio sample is placed 
into the blanking parts that follow the leading equalizing pulses, into 
each of the blanking parts that follow the trailing equalizing pulses, and 
into each of the horizontal scan lines of the vertical blanking portion 
that are used to transmit test signals. 
In the video receiver apparatus of the present invention, an audio sample 
that is narrower than the audio sample that was placed into the luminance 
portion, is removed, a sample and hold circuit provides a stepped output, 
and filtering smooths the stepped output into an audio output that is 
suitable for voice transmission. 
That is, in the present invention, an audio sample is placed inside the 
luminance portion of the horizontal composite signal, thereby allowing a 
relatively long time period for the audio sample, such as 3 microseconds. 
Also, since the audio signal is placed near the back porch, there is a 
minimum distance from the leading edge of the horizontal sync pulse to the 
audio sample, thereby allowing simplicity and economy of design while, at 
the same time, providing accuracy in placement and retrieval of the audio 
samples. 
Further, since the period of the blanking parts following the equalizing 
pulses is quite wide, audio samples placed into these blanking parts can 
have a relatively long time duration, such as 3 microseconds. In like 
manner, audio samples placed into the scan lines provided for test signals 
can have at least as long a time duration as audio samples placed into the 
luminance portion of the horizontal composite signals. Thus, for audio 
samples placed into these additional places, simplicity, economy of 
design, and accuracy are achieved in the present invention. 
Because the audio samples can have a relatively long time duration, and the 
audio samples are close to the leading edge of a horizontal sync pulse, or 
close to the leading edge of an equalizing pulse, the present invention 
minimizes the accuracy that is required of circuit components, the 
complexity in circuitry that is required, and cost of the video 
transmitter. 
In the receiver, a 1 microsecond audio sample is retrieved from the 3 
microsecond audio sample that was placed into the luminance portion by the 
transmitter. Because of being able to retrieve an audio sample of 
relatively short time duration from an audio sample of relatively long 
time duration, and because of the proximity of the audio sample to a 
leading edge of a sync, the present invention minimizes the accuracy that 
is required of circuit components, the complexity in circuity that is 
required, and video receiver cost. 
It should be understood that each audio signal is biased to have a 
magnitude that puts it into the luminance range, whether placed into the 
luminance portion, into the leading equalizing pulses, into the trailing 
equalizing pulses, or into the horizontal scan lines that are included in 
the vertical blanking portion. Therefore, audio information becomes a part 
of the picture, and because of this it may sometimes be necessary to 
adjust the magnification of the picture, or its placement on the video 
screen, so that the audio information is not seen. 
The present invention also provides a breakthrough in simplicity and low 
cost in that there is no requirement for storing audio signals, no need 
for time compressing the audio signal, and no need for expanding the time 
domain of time compressed signals. 
Instead, in the video transmitter apparatus of the present invention, only 
one audio sample is taken for each luminance portion, each equalizing 
pulse, and each test signal of the blanking portion. Then, low pass 
filtering is used to prevent ambiguity that could be caused by Nyquist 
phenomenon. 
In the video receiver apparatus of the present invention, a sample and hold 
circuit of simple design provides a stepped audio output. 
Also, circuitry complexity and cost have ben minimized by holding a 
previous audio sample during the time period of a vertical sync pulse. 
More particularly, the stepped output is held from the last blanking part 
that follows a leading equalizing pulse, during the time duration of the 
vertical sync pulse, and to the blanking part that follows the first 
trailing equalizing pulse. 
Low pass filtering removes noise and smooths the stepped audio output; and 
high pass filtering eliminates noise that would be caused by holding one 
audio pitch for this time duration. The result of both high pass and low 
pass filtering of the stepped audio output is audio quality that is quite 
adequate for voice transmission. 
Finally, by placing audio samples inside the luminance portion, by locating 
the audio samples close to the back porch, by placing additional audio 
samples onto the blanking parts that follow the leading and trailing 
equalizing pulses, by placing one audio sample into each text signal of 
the vertical blanking portion, by holding a previous audio sample across 
the vertical sync pulses, and by avoiding both time-compression and 
time-expansion techniques, apparatus and method have been provided that 
minimizes bandwidth, minimizes complexity, minimizes component cost, and 
optimizes performance vs. unit cost. 
In a first aspect of the present invention, a method is provided for 
inserting an audio signal into a composite video signal having a front 
porch, a horizontal sync pulse, a back porch, and a luminance portion, 
which method comprises sampling a magnitude of the horizontal sync pulse; 
sampling a magnitude of the audio signal; holding one of the sampled 
magnitudes; performing the sampling of the other of the magnitudes during 
the holding step; combining the sampled audio signal magnitude, the 
sampled horizontal sync magnitude, and a bias magnitude to provide an 
audio plus magnitude; performing a part of the combining step during the 
holding step; and replacing a first part of the composite video signal 
with the audio plus magnitude. 
In a second aspect of the present invention, a method is provided for 
inserting an audio signal into a composite video signal having a front 
porch, a horizontal sync pulse, a back porch, and a luminance portion, 
which method comprises sampling a magnitude of the horizontal sync pulse, 
sampling a magnitude of the audio signal; performing the sampling of the 
horizontal sync magnitude prior to the sampling of the audio signal 
magnitude; summing the horizontal sync magnitude with a bias magnitude; 
holding the summed magnitude; performing the sampling of the audio signal 
magnitude during the holding step; combining the sampled audio signal 
magnitude, the sampled horizontal sync magnitude, and the bias magnitude 
to provide an audio plus magnitude; completing the combining step during 
the holding step; and replacing a part of the composite video signal with 
the audio plus magnitude. 
In a third aspect of the present invention, a method is provided for 
separating an audio signal from a composite video signal having a 
horizontal sync pulse, a back porch, a luminance portion, a front porch, 
and a vertical sync pulse, which method comprises sampling the voltage of 
the horizontal sync pulse; holding the sampled horizontal sync voltage; 
sampling the voltage of a first part of the composite video signal into 
which a first audio plus voltage has been inserted; the sampling of the 
first part comprises sampling the first audio plus voltage during the 
holding step; reducing the sampled first part to a sampled audio voltage 
by subtracting the sum of the sampled horizontal sync voltage and a bias 
voltage; and the reducing step comprises summing the sampled horizontal 
sync voltage and the bias voltage, holding the summed voltage, and 
subtracting the summed voltage from the sampled first audio plus voltage 
during both of the holding steps. 
In a fourth aspect of the present invention, a method is provided for 
separating an audio signal from a composite video signal having a 
horizontal sync pulse, a back porch, a luminance portion, a front porch, 
and a vertical sync pulse, which method comprises sampling the voltage of 
the horizontal sync pulse; sampling the voltage of a first part of the 
composite video signal into which a first audio plus voltage has been 
inserted; holding one of the sampled voltages; performing the other 
sampling step during the holding step; holding the other of the sampled 
voltages; reducing the first sampled part to a first sampled audio voltage 
by subtracting the sum of the sampled horizontal sync voltage and a bias 
voltage; and performing a part of the reducing step during both of the 
holding steps. 
In a fifth aspect of the present invention, a method is provided for 
separating an audio signal from a composite video signal having a 
horizontal sync pulse, a back porch, a luminance portion, a front porch, 
and a vertical sync pulse, which method comprises sampling the voltage of 
the horizontal sync pulse; sampling the voltage of a first part of the 
composite video signal into which a first audio plus voltage has been 
inserted; reducing the sampled voltage of the first part to a first 
sampled audio voltage by subtracting the sum of the sampled horizontal 
sync voltage and a bias voltage; sampling a voltage of a part of a leading 
equalization pulse into which a second audio plus voltage has been 
inserted; sampling a voltage of a part of a trailing equalization pulse 
into which a third audio plus voltage has been inserted; sampling a 
voltage of a portion of a test signal into which a fourth audio plus 
voltage has been inserted; and reducing the second, third, and fourth 
audio plus voltages to second, third, and fourth sampled audio voltages. 
In a sixth aspect of the present invention, a method is provided for 
separating an audio signal from a demodulated composite video signal 
having a horizontal sync pulse, a back porch, a luminance portion, a front 
porch, and a vertical blanking portion with a vertical sync pulse, which 
method comprises separately floating the demodulated composite video 
signal around higher and lower voltages; sampling the magnitude of a part 
of the composite video signal that lies partially within the luminance 
portion at one of the floating voltages; holding the sampled magnitude; 
replacing the held sampled magnitude with successively sampled magnitudes; 
biasing the sampled magnitudes; and the biasing step comprises sampling 
the composite video signal at the other of the floating voltages. 
In a seventh aspect of the present invention, a method is provided for 
separating an audio signal from a demodulated composite video signal 
having a horizontal sync pulse, a back porch, a luminance portion, a front 
porch, and a vertical blanking portion with a vertical sync pulse, which 
method comprises separately floating the demodulated composite video 
signal around higher and lower magnitudes; sampling a horizontal sync 
pulse magnitude from the higher floated signal; sampling the magnitude of 
a first part of the composite video signal that lies partially within the 
luminance portion from the lower floated signal; holding the sampled 
magnitude of the first part; replacing the held sampled magnitude with 
successively sampled magnitudes; biasing the successively sampled 
magnitudes; and the biasing step comprises reducing one of the sampled 
magnitudes of the lower floated signal by the sampled magnitude of the 
higher floated signal. 
In an eight aspect of the present invention, a method is provided for 
inserting an audio signal into a composite video signal having a front 
porch, a horizontal sync pulse, a back porch, and a luminance portion, 
which method comprises floating the composite video signal at a different 
voltage in each of two separate paths; sampling the composite video signal 
in one of the separately-floated paths; using the sample to bias the audio 
signal; and using the biased audio signal to replace a portion of the 
video signal in the other of the separately-floated paths.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1 and 2, a black and white composite video signal 10 
includes a plurality of black and white horizontal composite signals 12, a 
first-field vertical blanking time, or vertical blanking portion, 13A, 
another plurality of the black and white horizontal composite signals 12, 
and a second-field vertical blanking time, or vertical blanking portion 
13B. 
Each black and white horizontal composite signal 12 includes information 
required to display a single horizontal scan line of black and white video 
(not shown), and also includes video information and information needed 
for timing and synchronizing the video information of each single 
horizontal scan line of video. 
One frame 14 of horizontal composite signals 12 includes a first video 
field 15A and a second video field 15B; and each video field, 15A or 15B, 
includes 2411/2 to 2491/2 black and white horizontal composite signals 12, 
and one vertical blanking time, 13A or 13B. The scan lines produced by a 
first video field 15A and a second video field 15B are interlaced to form 
one frame 14 of video. 
Typically, the horizontal scan rate is 15,750 Hertz, so each of the 
horizontal composite signals 12 has a period of 1.0 H, or 63,492 
microseconds. Each horizontal composite signal 12 includes a luminance 
portion 16 having a time duration of 0.84 H or 53.5 microseconds, which 
contains the video picture information, and a horizontal blanking portion 
18 having a time duration of 0.16 H or 10.16 microseconds. 
Referring now to FIGS. 1-3, and more particularly to FIG. 3, each of the 
horizontal blanking portions 18 includes a horizontal sync pulse 20 with a 
leading edge 22, a front porch 24, and a back porch 26. The front porch 24 
has a time duration of 0.02 H, or 1.27 microseconds, the horizontal sync 
pulse 20 has a time duration of 0.08 H, or 5.07 microseconds, and the back 
porch 26 has a time duration of 0.06 H, or 3.81 microseconds. 
Referring now to FIGS. 4 and 5, a color horizontal composite signal 28 
includes the luminance portion 16, as described in conjunction with FIGS. 
1 and 2, and a horizontal blanking portion 30. The luminance portion 16 is 
identical to the luminance portion 16 of FIGS. 1-3, and the horizontal 
blanking portion 30 includes parts as named and numbered, and having time 
durations, and as described in conjunction with the horizontal blanking 
portion 18 of FIG. 3, except that the horizontal blanking portion 30 of 
FIGS. 4 and 5 includes a back porch 32. 
The back porch 32 of FIG. 5 differs from the back porch 26 of FIG. 3 only 
by a color burst 34 being inserted therein. The color burst 34 is 8 to 10 
cycles at 3.58 megahertz, thereby taking from 2.24 to 2.79 microseconds of 
the 3.81 microsecond time duration of the back porch 32. 
Referring now to FIG. 2, the horizontal composite signal 12 includes a 
composite magnitude 36 that is the sum of a horizontal blanking magnitude 
38 and a luminance magnitude 40. The horizontal blanking magnitude 38 is 
maintained at a constant peak-to-peak voltage, but the luminance magnitude 
40 varies in peak-to-peak voltage depending on the picture information. 
The maximum signal level for the composite magnitude 36 is 1.00 volt 
peak-to-peak, which includes 0.25 volts for the horizontal blanking 
magnitude 38, leaving a maximum of 0.75 volts peak-to-peak for the 
luminance magnitude 40. The luminance magnitude 40 is always positive with 
respect to the horizontal blanking magnitude 38, the horizontal sync pulse 
20 is negative with respect to the horizontal blanking magnitude 38 and 
extends negatively to a horizontal sync magnitude, or blacker-than-black 
magnitude, 42. 
Although not shown herein, but as is well known to those skilled in the 
art, whether the composite video signal 10 is amplitude or frequency 
modulated, it is standard practice to place audio on sidebands separate 
from the composite video signal 10. 
Also, as is well known to those skilled in the art, the horizontal 
composite signals, 12 or 28, transmit the video signal within the 
luminance portion 16, and control horizontal synchronizing functions by 
the leading edges 22 of successive ones of the horizontal sync pulses 20 
in the horizontal blanking portions, 18 or 30. 
Referring now to FIGS. 1 and 6, the vertical blanking portions, 13A and 
13B, are each divided up into a leading equalizing period 44 having six 
leading equalizing pulses 46, a vertical sync pulse 48 with serrations 50 
in a vertical sync period 52, a trailing equalizing portion 54 having six 
trailing equalizing pulses 56, and 10 to 21 test signals, 58. 
Each of the test signals 58 results in one horizontal scan line, so there 
are 10 to 21 scan lines that do not include a luminance portion 16. 
However, each of the test signals 58 includes a horizontal sync pulse 20 
and a blanking portion 60. The blanking portions 60 of the test signals 58 
are used by broadcasters to transmit useful test information. 
The leading equalizing period 44, the vertical sync period 52, and the 
trailing equalizing portion 54 each has a time duration of 3.0 H, or 
190.48 microseconds. The equalizing pulses, 46 and 56, each has a time 
duration of 0.04 H, or 2.543 microseconds; the serrations 50 of the 
vertical sync pulse 48 have a time duration of 0.43 H, or 27.30 
microseconds; and each of the test signals 58 has the same time duration 
as the horizontal composite signals 12. That is, each of the test signals 
58 has a time duration of 1.0 H, or 63.492 microseconds. 
The purpose of the equalizing pulses 46 and 56 is to provide a smooth 
transition between first and second video fields, 15A and 15B, that is, to 
provide a smooth transition in interlacing scan lines of the first and 
second video fields, 15A and 15B. 
All of these functions are the same whether black and white or color video 
is transmitted. However when color is transmitted, the color burst 34 is 
included in the back porch 32 of the horizontal blanking portion 30. 
Additional basic principles of transmitting and receiving video can be 
found in Electronic Communications Systems by Wayne Tomasi, published by 
Prentice Hall in Englewood Cliffs, N.J. in 1988, pages 452-483, and 
incorporated herein by reference, although additional information is not 
essential to understanding the present invention. 
It should be understood that the invention disclosed herein works equally 
well with either black and white or color video. That is, the present 
invention works equally well whether or not the horizontal composite 
signals, 12 or 28, include the color burst 34 on the back porch, 26 or 32. 
Referring now to the block diagram of FIG. 7, in the present invention 
video transmitter apparatus 70 is used to multiplex one or more audio 
signals, or other nonvideo information, into the luminance portion 16 of 
the horizontal composite signal, 12 or 28, or at least partially into the 
luminance portion 16. 
The video transmitter apparatus 70 is interposed into a standard video 
transmitter (not shown), subsequent to placing picture information into 
the luminance portion 16 of the horizontal composite signal 12, and prior 
to modulating the horizontal composite signal 12. 
In the video transmitter apparatus 70, the composite video signal 10 of 
FIG. 1 enters the video transmitter apparatus 70 at a video input arrow 
72. As has been described previously, the composite video signal 10 
includes a plurality of horizontal composite signals, 12 or 28. 
The following discussion focuses on placing audio signals into the 
luminance portion 16 of the horizontal composite signals, 12 and 28, as 
opposed to placing audio signals into other parts of the composite video 
signal 10. Later, it will be shown that the video transmitter apparatus 70 
also places audio signals, or other audio information, into other parts of 
the composite video signal 10. 
Since operation is the same whether black and white or color video is 
transmitted, reference will be made only to the black and white horizontal 
composite signals 12. 
Horizontal composite signals 12 of the composite video signal 10, as shown 
in FIGS. 1 and 2, are supplied to the video input arrow 72. However, the 
horizontal composite signals 12, as supplied to the video input arrow 72, 
are floating, as shown by a floating video signal 74 of FIG. 8. The 
floating video signals 74 are delivered from the video input arrow 72 to a 
buffer 76 via a conductor 78; and a video bias supply 80 delivers a video 
bias voltage to the buffer 76 via a conductor 82. 
The buffer 76 cooperates with the video bias supply 80 to supply a 
4.0-biased video signal 84, as shown in FIG. 9, to a conductor 85, which 
is the same as the floating video signal 74 of FIG. 8 except biased 4.0 
volts. Also, the buffer 76 cooperates with the video bias supply 80 to 
supply a 4.7-biased video signal 86, as shown in FIG. 10, to a conductor 
88, which is the same as the floating video signal 74 of FIG. 8 except 
biased 4.7 volts. Therefore, the composite video signal 10 is floated in 
two separate flow paths at two different voltages. The composite video 
signal 10 is floated at 4.0 volts in a flow path that is provided by the 
conductor 85, and the composite video signal 10 is floated at 4.7 volts in 
a flow path that is provided by the conductor 98. 
The purpose for biasing the floating video signal 74 by 4.0 volts is to 
provide inputs for amplifiers that are roughly one half of the 8.0 volt 
magnitude of a regulated power supply (not shown, not an inventive part of 
the present invention) that is supplied to the amplifiers. The purpose for 
biasing the floating video signal 74 by 4.7 volts will be shown 
subsequently. 
The 4.7-biased video signal 86 is delivered by the conductor 88 and a 
conductor 90 to a sync detector 92, and is delivered to a 4.7-biased video 
input 94 of a sample and hold circuit 96 by the conductor 88 and a 
conductor 98. 
The sync detector 92 detects the leading edge 22 of the horizontal sync 
pulse 20, as more clearly seen in FIGS. 3 and 5. The sync detector 92 
delivers a trigger pulse to a 1 microsecond one-shot 100, via conductors 
102, 104, and 106, that coincides with the timing of the leading edge 22 
of the horizontal sync pulse 20. 
The sync detector 92 delivers the same trigger pulse to a 10 microsecond 
one-shot 108 via the conductor 102 and a conductor 110; and the sync 
detector 92 delivers the same trigger pulse to an auxiliary input 112 of a 
3 microsecond one-shot 114 via the conductors 102 and 104, and a conductor 
116. 
The 1 microsecond one-shot 100, as it receives the trigger pulse from the 
sync detector 92, provides a 1 microsecond sample pulse to a trigger input 
118 of the sample and hold circuit 96 via a conductor 120. The sample and 
hold circuit 96 then samples a 4.7-biased horizontal sync magnitude 122 of 
the horizontal sync pulse 20 of FIG. 10 which, being derived from the 
4.7-biased video signal 86 of FIG. 10, and being supplied to the 
4.7-biased video input 94, is 4.7 volts greater than a floating horizontal 
sync magnitude 124 of the horizontal sync pulse 20 of FIG. 8. The 
4.7-biased horizontal sync magnitude 122 is delivered from the sample and 
hold circuit 96 to a first input 126 of a summer 128 via a conductor 130. 
During this time, a positively and negatively varying audio signal 132 of 
FIG. 11 has been supplied from an audio input arrow 133, via a conductor 
134, to an amplifier 136 having automatic gain control. The amplifier 136 
delivers the varying audio signal 132 to a low pass filter 138 via a 
conductor 140, and the low pass filter 138 delivers the varying audio 
signal 132 to a second input 142 of the summer 128 via a conductor 144. 
The low pass filter 138 is designed in accordance to the Nyquist criteria, 
and uses a three pole Chebychev circuit to limit the varying audio signal 
132 to a 5 kilohertz bandwidth. This frequency range is sufficient to 
accommodate audio communication, but not high fidelity music. Preferably, 
the low pass filter 138 reduces the audio signal 132 by 3 dB at 5 
kilohertz. 
Therefore, the positively and negatively varying audio signal 132 of FIG. 
11, as amplified and filtered by the amplifier 136 and the filter 138, is 
added to the 4.7-biased horizontal sync magnitude 122 of FIG. 10 in the 
summer 128, to provide a 4.7-biased audio signal 146, as shown in FIG. 12. 
That is, the 4.7-biased audio signal 146 is equal to the sum of the 
positively and negatively varying audio signal 132 of FIG. 11, the 
floating sync magnitude 124 of FIG. 8, and a bias of 4.7 volts. 
Returning now to the 10 microsecond one-shot 108 and the 3 microsecond 
one-shot 114, when the 10 microsecond one-shot 108 receives a trigger 
pulse from the sync detector 92, it starts a 10 microsecond delay from the 
leading edge 22 of the horizontal sync pulse 20. At the end of the 10 
microsecond delay, the one-shot 108 delivers a trigger signal to a primary 
input 148 of the 3 microsecond one-shot 114 via a conductor 149. 
The 3 microsecond one-shot 114 provides a Q output to a Q conductor 140 for 
a period of 3 microseconds. At all other times the 3 microsecond one-shot 
114 provides a NOT-Q output to a NOT-Q conductor 152. 
An analog switch 154 includes a first control input 156 that is connected 
to the Q conductor 150, a second control input 158 that is connected to 
the NOT-Q conductor 152, an audio input 160, a video input 162, and an 
output 164. 
The audio input 160 is connected to an output 166 of the summer 128 via a 
conductor 168; so that the 4.7-biased audio signal 146 of FIG. 12 is 
continuously supplied to the audio input 160 of the analog switch 154. 
Not only is the 4.7-biased audio signal 146 of FIG. 12 continuously applied 
to the audio input 160 of the analog switch 154; but also the 4.0-biased 
video signal 84 of FIG. 9 is continuously supplied to the video input 162 
of the analog switch 154. 
At all times except during a 3 microsecond interval in which the Q output 
signal exists in the Q conductor 150, the analog switch 154 communicates 
the video input 162 to the output 164, thereby delivering the 4.0-biased 
video signal 84 of FIG. 9 to a buffer 170 via a conductor 172, and to an 
audio-on-video output 174 via a conductor 176. 
However, for a period 178, as shown in FIG. 13, which starts 10 
microseconds after the leading edge 22 of the horizontal sync pulse 20, 
and which continues for 3 microseconds, the Q output signal exists in the 
Q conductor 150, and the analog switch 154 blocks communication from the 
video input 162 to the output 164, thereby effectively removing a video 
part 180, as shown in FIG. 13, of the luminance portion 16 of the 
4.0-biased video signal 84. 
Also, during this 3 microsecond time period, the analog switch 154 
communicates the audio input 160 of the analog switch 154 to the output 
164, thereby delivering an audio part, or nonvideo part, 182, as shown in 
FIG. 14, from the audio input 160 of the analog switch 154 to the output 
164 thereof. The audio part 182 also has the period 178, as shown in FIG. 
14. 
The result is an audio-on-video signal 184 at the output 164 of the analog 
switch 154. The audio-on-video signal 184, which includes the audio part 
182, is shown in FIG. 15. 
That is, the output 164 of the analog switch 154 delivers a signal to the 
buffer 170 via the conductor 172 that consists of the 4.0-biased video 
signal 84 of FIG. 9, minus the video part 180 of FIG. 13, plus the audio 
part 182 of FIG. 14, thereby providing the audio-on-video signal 184 of 
FIG. 15. 
As shown in FIG. 16, the audio part 182 has an audio plus magnitude 186 
that is the sum of the floating horizontal sync magnitude 124 of FIG. 8, a 
bias 188 of 4.7 volts, and an audio magnitude 190 of the audio signal 132. 
Or, as shown in FIG. 17, the audio plus magnitude 186 of the audio part 
182 is equal to the sum of the floating horizontal sync magnitude 124 of 
FIG. 8, a bias 192 of 4.0 volts, a bias 194 of 0.7 volts, and the audio 
magnitude 190. 
If it were not for this bias 914 of 0.7 volts, negative magnitudes of the 
audio signal 132 of FIG. 11 would push the audio plus magnitude 186 down 
into the range between a horizontal blanking magnitude 196 and a 
horizontal sync magnitude 198, both of FIG. 15. 
If audio magnitudes 190 were to descend below the horizontal blanking 
magnitude 196, they could interfere with timing of the scan lines (not 
shown) as controlled by the leading edge 22 of the horizontal sync pulse 
20. 
As described above, the video part 180 that has been removed from the 
4.0-biased video signal 84 of FIG. 13, and the audio part 182 of FIG. 14 
that has been inserted into the 4.0-biased video signal 84 of FIG. 13 to 
make the audio-on-video signal 184 of FIG. 15 are both proximal to the 
back porch, 26 or 32. 
Alternately, by increasing the time delay of the 10 microsecond one-shot 
108, the Q conductor 150 is energized later, and a video part 200, as 
shown in FIG. 13, that is proximal to the front porch 24, is removed from 
the 4.0-biased video signal 84; and the removed video part 200 is replaced 
by an audio part, or nonvideo part, 202, as shown in FIG. 15. 
Or, by energizing the Q conductor 150 10 microseconds after the leading 
edge 22 of the horizontal sync pulse 20, and also energizing the Q 
conductor 150 after a longer delay, both video parts, 180 and 200, will be 
removed from the 4.0-biased video signal 84, and both of the audio parts, 
182 and 202, will be inserted into the 4.0-biased video signal 84 to form 
the audio-on-video signal 184 of FIG. 15. That is, as shown in FIG. 15, 
one audio part, or nonvideo part, 182 may be inserted into the luminance 
portion 16 proximal to the front porch 24, and another audio part, or 
nonvideo part, 182 may be inserted into the luminance portion 16 proximal 
to the back porch 26. 
Referring to FIG. 7, the operation of the transmitter apparatus 70 
continues as described until the vertical blanking portion, 13A or 13B, 
occurs. However, before considering operation of the present invention 
during the vertical blanking portions, 13A and 13B, it is important to 
consider additional facts about the operation of the video transmitter 
apparatus 70. 
When a horizontal sync pulse 20 occurs, a signal of 5.07 microseconds 
duration is sent to the auxiliary input 112, thereby disabling the 3 
microsecond one-shot 114 for 5.07 microseconds. However, the 10 
microsecond one-shot 108 applies a trigger signal to the primary input 148 
of the 3 microsecond one-shot 114 after 10 microseconds. 
Therefore, the sync detector 92 and the 10 microsecond one-shot 108 
cooperate with the horizontal sync pulse 20 to produce a 3 microsecond 
output from the 3 microsecond one-shot 114 that occurs between 10 and 13 
microseconds after the leading edge 22 of the horizontal sync pulse 20. 
However, when the vertical sync pulse 48 of FIG. 6 occurs, since the time 
duration of the serrations 50 of the vertical sync pulses 48 are 27.30 
microseconds, one of the serrations 50 is still applying a disable signal 
to the auxiliary input 112, and is still disabling the 3 microsecond 
one-shot 114 after the 10 microsecond one-shot 108 has attempted to 
activate the 3 microsecond one-shot 114. 
Therefore, during the vertical sync pulse 48, the 3 microsecond one-shot 
114 continues to produce a NOT-Q output in the NOT-Q conductor 152; and 
the analog switch 154 delivers the 4.0-biased video signal 84 from the 
video input 162 to the output 164 of the analog switch 154 continuously 
during the entire vertical sync period 52 of the vertical sync pulse 48, 
including all serrations 50 thereof. 
However, as noted previously, the leading and trailing equalizing pulses, 
46 and 56, of FIG. 6 each has a time duration of only 2.543 microseconds; 
so the sync detector 92 delivers a trigger signal to the auxiliary input 
112 of the 3 microsecond one-shot 114 for only 2.543 microseconds. Thus 
the 10 microsecond one-shot 108 delivers a trigger signal to the 3 
microsecond one-shot 114 after termination of a disable signal from the 
auxiliary input 112 of the 3 microsecond one-shot 114. 
Referring to FIGS. 6, 17 and 18, the result is that the 3 microsecond 
one-shot 114 is actuated between 10 and 13 microseconds after a leading 
edge 204 of the equalizing pulse, 46 or 56. Since two equalizing pulses, 
46 or 56, and two blanking parts 206 that are interposed between pairs of 
equalizing pulses, 46 or 56, have a total time duration of 1.0 H, and 
since the equalizing pulses, 46 and 56, are 2.432 microseconds wide, each 
blanking part 206 is 29.2 microseconds in width. 
Therefore, the 3 microsecond one-shot 114 is triggered 7.457 microseconds 
after a trailing edge 208 of each equalizing pulse, 46 or 56; and, as 
shown in FIG. 18, an audio part 212 that is 3 microseconds wide is 
inserted into the blanking part 206. The audio part 212 starts 7.457 
microseconds after the trailing edge 208 of an equalizing pulse, 46 or 56, 
and ends 10.457 microseconds after the trailing edge 208. 
Referring now to FIGS. 6 and 19, as previously noted, 10 to 21 test signals 
58 are included into the video fields, 15A and 15B, subsequent to the 
trailing equalizing pulses 56, and each of the test signals 58 includes 
both a horizontal sync pulse 20 with a leading edge 22, and a blanking 
portion 60. 
Since the horizontal sync pulses 20 of the test signals 58 each has a width 
of 5.07 microseconds, the apparatus of the present invention places audio 
parts 214, as shown in FIG. 19, into each of the test signals 58; and the 
audio parts 214 are located between 10 and 13 microseconds from the 
leading edge 22 of the horizontal sync pulse 20. The remainder of each of 
the blanking portions 60 is available for insertion of any test 
information that a broadcaster may wish to transmit. 
As previously noted, the video transmitter apparatus 70 of FIG. 7 is 
interposed into a standard video transmitter (not shown) subsequent to the 
video information being placed into the luminance portion 16, but prior to 
modulation. The floating video signal 74 that enters at the video input 
arrow 72 is floating about zero volts; but the audio-on-video signal 184 
that exits at the audio-on-video output 174 is biased. 
At the audio-on-video output 174, the 4.0-biased video signal 84 of FIG. 13 
is biased by 4.0 volts, and the audio parts, 182 and 202, of FIG. 15 are 
biased 4.7 volts above the horizontal sync magnitude 124 of FIG. 8. 
However, the audio-on-video output 174 is coupled back into the video 
transmitter (not shown) by a capacitor (not shown). Thus, by AC coupling 
the video transmitter apparatus 70 back into the video transmitter, the 
bias is removed, leaving an audio-on-video signal (not shown) that is the 
same as the audio-on-video signal 184 of FIG. 16, except that the 4.0 volt 
bias has been removed. 
Referring now to FIG. 20, video receiver apparatus 220 is provided for use 
in a video receiver (not shown) for recovering audio from a demodulated 
audio-on-video signal 222 of FIG. 21A wherein one or more audio signals, 
such as audio parts, or nonvideo parts, 224 and/or 226, have been 
interposed into the horizontal composite signal 12 of FIG. 2. 
The receiver apparatus 220 is interposed into a video receiver (not shown) 
that is standard, except that, since audio is not included on sidebands, 
no provisions are included for dealing with audio signals on sidebands. 
More particularly, the receiver apparatus 220 is patched into the video 
receiver (not shown) subsequent to demodulation. 
As shown in FIG. 21A, the audio parts 224 and 226 are disposed in a 
luminance portion 228 of the audio-on-video signal 222. That is, 
preferably one or more of the audio parts, 224 or 226, are disposed, at 
least partially, within the luminance portion 228. 
Referring now to FIG. 22, the audio part 224 includes an audio plus 
magnitude 230; and the audio plus magnitude 230 is the sum of a horizontal 
sync magnitude 232, a bias magnitude 234 of 0.7 volts that was added by 
the transmitter apparatus 70 of FIG. 7, and an audio magnitude 236. As 
shown in FIG. 21A, the audio-on-video signal 222 is biased 4.0 volts; and 
as shown in FIG. 22, the audio plus magnitude 230 is biased 4.0 volts. 
The bias magnitude 234 of 0.7 volts, that was added to the audio signal 132 
of FIG. 11 in the video transmitter apparatus 70 of FIG. 7, has placed a 
zero magnitude, or zero amplitude 238 of the audio plus magnitude 230 
close, in magnitude, to a midpoint 240, as shown in FIG. 21A, of a maximum 
luminance magnitude 242. 
Therefore, for both positive and negative values of audio magnitudes 236, 
placing the zero magnitude 238 at the midpoint 240 of the maximum 
luminance magnitude 242 allows a maximum variation in audio magnitude 236 
without the audio plus magnitude 230 going above the maximum luminance 
magnitude 242 or below a horizontal blanking magnitude 244. 
Referring again to FIG. 20 and the video receiver apparatus 220, the 
audio-on-video signal 222 of FIG. 21A is supplied to the receiver 
apparatus 220 at a video input arrow 246, and the audio-on-video signal 
222 is applied to a buffer 248 via a conductor 250. 
The buffer 248 buffers the audio-on-video signal 222 and supplies it to a 
conductor 251; and the buffer 248 supplies a 4.7-biased audio-on-video 
signal 252, as shown in FIG. 23, to a conductor 254. As its name implies, 
the 4.7-biased audio-on-video signal 252 is biased 0.7 volts above the 
audio-on-video signal 222 as supplied at the video input arrow 246, which 
is biased 4.0 volts. 
The buffer 248 is connected to a sync detector 256 by a conductor 258, and 
the sync detector 256 detects the leading edge 22 of the sync pulse 20 of 
FIG. 3. When the sync detector 256 detects the leading edge 22 of the sync 
pulse 20, it sends a trigger pulse to an 11 microsecond one-shot 260 via 
conductors 262 and 264. At the end of 11 microseconds, the one-shot 260 
sends a trigger signal to a primary input 266 of a 1 microsecond one-shot 
268 via a conductor 270. 
In response to the trigger signal from the 11 microsecond one-shot 260, the 
1 microsecond one-shot 268 sends a sample enable signal to a signal enable 
input 272 of a sample and hold circuit 274 via a conductor 276. The sample 
and hold circuit 274 also receives the audio-on-video signal 222. That is, 
the audio-on-video signal 222 is continuously applied to an audio sample 
input 278 of the sample and hold circuit 274 by the conductor 251. 
Therefore, in response to a sample enable signal from the 1 microsecond 
one-shot 268, the sample and hold circuit 274 samples the audio plus 
magnitude 230 of the audio part 224 of FIG. 22 for 1.0 microsecond to 
produce an audio sample magnitude 280, as shown in FIG. 21B, and holds the 
audio sample magnitude 280 until the next sample enable signal. That is, 
the sampling period occurs at a time that starts 11 microseconds after the 
leading edge 22 of the horizontal sync pulse 20, and that ends 12 
microseconds after the leading edge 22. 
Referring now to FIGS 20, 21A, and 21B, since the sample and hold circuit 
274 takes the sample magnitude 280 between 11 and 12 microseconds after 
the leading edge 22 of the sync pulse 20, the sample magnitude 280 is 
taken exactly in the middle of the audio part 224 that started 11 
microseconds after the leading edge 22 and ended 12 microseconds after the 
leading edge 22. 
The sample magnitude 280 is delivered to an audio sample input 282 of a 
differential amplifier 284 by a conductor 286. As shown in FIG. 21B, the 
audio sample magnitude 280 is held constant until replaced by a new audio 
sample magnitude 288, which is taken between 11 and 12 microseconds after 
the next leading edge 22 of the next horizontal sync pulse 20. 
The sync detector 256 also delivers a trigger pulse, that corresponds to 
the leading edge 22 of the horizontal sync pulse 20, to a 1 microsecond 
one-shot 290 via the conductor 262 and a conductor 292. And, the 1 
microsecond one-shot 290 delivers a trigger pulse to a trigger input 294 
of a sample and hold circuit 296 via a conductor 298. During this time, 
and also continuously, the 4.7-biased audio-on-video signal 252 of FIG. 23 
is supplied to a biased input 300 of the sample and hold circuit 296 by 
the conductor 254. 
When triggered by the 1 microsecond one-shot 290, the sample and hold 
circuit 296 samples a 4.7-biased horizontal sync magnitude 302, as shown 
in FIG. 23, of the 0.7-biased audio-on-video signal 252 which is 
continuously supplied to the biased input 300, holds the sync magnitude 
302 until replaced by a new magnitude, and delivers the sync magnitude 302 
to a biased input 304 of the differential amplifier 284 via a conductor 
306. 
The sample and hold circuit 296 takes samples of the 4.7-biased 
audio-on-video signal 252 at a time that is 1.0 microsecond after the 
leading edge 22 of the horizontal sync pulse 20. Thus, the sample is taken 
during the 5.07 microseconds of the horizontal sync pulse 20; and the 
sample is the 4.7-biased horizontal sync magnitude 302 of FIG. 23. 
As shown above, the differential amplifier 284 is provided with two inputs, 
282 and 304, both of which are held until some time with respect to the 
next leading edge 22 of the horizontal sync pulse 20. At the audio sample 
input 282, the audio sample magnitude 280 of the audio part 224 is held 
constant until replaced by the audio sample magnitude 288, 11 microseconds 
after the succeeding horizontal sync pulse 20. 
The differential amplifier 284 delivers a voltage to an output 308 thereof 
that is equal to the audio plus magnitude 230 of FIG. 22, as applied to 
the audio sample input 282, minus the bias magnitude 234 of 0.7 volts of 
FIG. 22, as applied to the biased input 304 of the differential amplifier 
284, all biased 4.0 volts as shown in FIG. 21A. 
As can be seen in FIG. 22, the difference between the audio plus magnitude 
230, such as the audio sample magnitudes, 280 and 288, of FIG. 21B, and 
the bias magnitude 234, is the audio magnitude 236. The audio magnitude 
236 is delivered from the differential amplifier 284 to a band-pass filter 
310 via a conductor 312. 
Continuing to refer to FIG. 20, when a horizontal sync pulse 20 occurs, the 
11 microsecond one-shot 260 actuates the 1 microsecond one-shot 268 at the 
end of 11 microseconds. 
During the horizontal sync pulse 20, that is, until 5.07 microseconds after 
the leading edge 22, the sync detector 256 sends a trigger pulse to an 
auxiliary input 314 of the 1 microsecond one-shot 268 via a conductor 316; 
and this trigger pulse at the auxiliary input 314 prevents the 1 
microsecond one-shot 268 from being actuated by the 11 microsecond 
one-shot 260 at the primary input 266. 
However, since the 11 microsecond one-shot 260 triggers the 1 microsecond 
one-shot 268 after 5.07 microseconds, the 1 microsecond one-shot 268 is 
triggered by the 11 microsecond one-shot 260. Therefore, a new audio 
sample magnitude, 280 or 288, of FIG. 21B is taken from each 
audio-on-video signal 222 of FIG. 21A. 
Referring now to FIGS. 6, 20, and 21A, in like manner, since the time 
duration of the equalizing pulses 46 and 56 is 2.543 microseconds, the 11 
microsecond one-shot 260 energizes the 1 microsecond one-shot 268 after 
cessation of the equalizing pulse, 46 or 56, thereby enabling the sample 
and hold circuit 274 to take a new audio sample magnitude 318 of the audio 
part 212 of FIGS. 18 and 21A. This new sample magnitude 318 is disposed in 
the blanking parts 206 that follow the leading equalizing pulses 46. In 
like manner, audio samples (not shown) will be placed into blanking parts 
206 that follow the trailing equalizing pulses 56. 
In contrast, the time duration of each serration 50 of the vertical sync 
pulse 48 is 0.43 H, or 27.30 microseconds. Therefore, since the time 
duration of each serration 50 is greater than 11 microseconds, a new audio 
sample magnitude, such as the sample magnitudes 280, 288, and 318, is not 
taken; but instead, a previously-taken audio sample magnitude, 318, is 
held. 
That is, each audio sample magnitude, 280, 288, or 318, is replaced by a 
new sample magnitude, 280 or 318, and is replaced 11 microseconds after 
the leading edge 22 of a horizontal sync pulse 20 during times when 
horizontal composite signals 12 are producing video. Also, an audio sample 
magnitude, 318, is held from the blanking part 206 of one equalizing 
pulse, 46 or 56, until the blanking part 206 of the next equalizing pulse, 
46 or 56; but it is only 0.5 H between equalizing pulses, 46 or 56. 
However, an audio sample magnitude, 280 or 288, is held from the last 
blanking part 206 of a leading equalizing pulses 46, during the 3.0 H of 
the vertical sync pulse 48, and until the first blanking part 206 
following the first trailing equalizing pulse 56. Thus, an audio sample 
magnitude 318 is held for a time period of approximately 4.0 H, or 254 
microseconds. 
Therefore, an audio sample magnitude 318 is held approximately four times 
longer during the vertical blanking portions, 13A and 13B, than an audio 
sample magnitude, 280 or 288, is held during a single scan line of a 
horizontal composite signal 12. 
High-pass filtering, as provided in the band-pass filter 310, prevents a 
"clicking" noise that would occur as an audio sample magnitude 318 is held 
during a vertical sync pulse 48. That is, high-pass filtering filters out 
noise that would be caused by holding a given audio sample magnitude 318 
for a time period of approximately 3.5 H. Preferably, the band-pass filter 
310 reduces frequencies of 250 Hertz by 3 dB. 
The band-pass filter 310 also provides low-pass filtering. Low-pass 
filtering, as provided by the band-pass filter 310, prevents errors that 
could occur due to Nyquist criteria, smooths a stepped audio output 320 of 
FIG. 21B into a smoothed audio output 322 of FIG. 21C, and also removes 
noise spikes (not shown) from the stepped audio output 320. Preferably, 
the low-pass filtering reduces a 5 kilohertz signal by 3 dB. The smoothed 
audio output 322 is delivered from the band-pass filter 310 to an audio 
output arrow 324 via a conductor 326. 
The smoothed audio output 32 allows audio frequencies in the range of 250 
Hertz to 5 kilohertz, which is entirely adequate for verbal 
communications; and, even though the smoothed audio output 322 has been 
obtained from the stepped audio output 320, any difference between the 
smoothed audio output 322 and audio which has not been obtained from 
stepped audio, such as the stepped audio output 320, is not recognizable 
to the ear. 
The present invention allows color video to be broadcast together with 
audio in a 10 megahertz bandwidth, as compared to a bandwidth that can 
exceed 25 megahertz for conventional color video transmitters. A part of 
this reduction in bandwidth is achieved by placing the audio on the video 
signal. Further reduction in the required bandwidth is achieved by 
reducing the percentage of modulation. 
As is well known, the required bandwidth is approximately equal to Carson's 
Rule. Carson's Rule states that the required bandwidth is equal to twice 
the sum of the maximum modulation frequency and the maximum frequency 
deviation. 
By placing audio on the horizontal composite signal 12, and thereby 
eliminating audio sidebands, the required bandwidth for color FM video in 
the 1900 megahertz band is reduced from 26 megahertz to 16.2 megahertz. 
That is, with a modulation frequency of 4.1 megahertz and with a 4.0 
megahertz deviation, the required bandwidth by Carson's Rule is 
2.times.(4.1+4.0)=16.2 megahertz. 
However, in the present invention, the deviation frequency is reduced from 
4 megahertz to 900 kilohertz. With this reduction in deviation, the 
required bandwidth for color FM video in the 1900 megahertz band, as 
calculated by Carson's Rule, is 2.times.(4.1+0.9)=10 megahertz. 
Further, the present invention allows black and white video to be broadcast 
together with audio in a 5 megahertz bandwidth, as compared to a bandwidth 
of 15-18 megahertz for conventional black and white video transmitters. A 
part of this reduction in bandwidth is achieved by placing the audio on 
the video signal. Further reduction in the required bandwidth is achieved 
by reducing the percentage of modulation. 
For convention transmission of black and white video, the maximum 
modulation frequency is 1.5 megahertz; and the maximum frequency deviation 
for black and white video, as well as for color video, is 4.0 megahertz. 
The bandwidth for black and white video, when transmitted in accordance 
with the principles of the present invention is reduced to 
2.times.(1.5+4.0)=11.0 megahertz. Further, by reducing the maximum 
frequency deviation to 1.0 megahertz, the bandwidth requirement is reduced 
to 2.times.(1.5+1.0)=5.0 megahertz. 
Therefore, the present invention permits color video to be broadcast in a 
10.0 megahertz bandwidth, permits black and white video to be broadcast in 
a 5.0 megahertz bandwidth, and opens up tremendous possibilities for 
business to utilize the benefits of video communications. 
Finally, in addition to reducing the required bandwidth, the present 
invention provides a video transmitter and a video receiver, both of which 
are of optimized simplicity. Both use circuitry of optimized simplicity 
and both use simple and low cost components. Therefore, in addition to 
providing video equipment for use in narrow bandwidth, the video 
transmitting and receiving equipment of the present invention achieve 
optimized economy of design and manufacturing. 
The method of the video transmitter apparatus 70 of FIG. 7 includes 
inserting the audio part, 182 or 202, of the audio signal 132 into the 
composite video signal 10 having the front porch 24, the horizontal sync 
pulse 20, the back porch 26, and the luminance portion 16. The steps of 
the method include sampling the audio part, 182 or 202, of the audio 
signal 132, removing the video part, 180 or 200, from the luminance 
portion 16 of the composite video signal 10, and replacing the video part, 
180 or 200, with the audio part, 182 or 202. 
Additional steps of the method of the video transmitter apparatus 70, and 
the method of the video receiver apparatus 220 of FIG. 20 can be 
understood by referring to the respective detailed descriptions. 
While specific apparatus and method have been disclosed in the preceding 
description, and while part numbers have been inserted parenthetically 
into the claims to facilitate understanding of the claims, it should be 
understood that these specifics have been given for the purpose of 
disclosing the principles of the present invention and that many 
variations thereof will become apparent to those who are versed in the 
art. Therefore, the scope of the present invention is to be determined by 
the appended claims, and without any limitation by the part numbers 
inserted parenthetically in the claims. 
INDUSTRIAL APPLICABILITY 
The present invention is applicable for use with video transmitters and 
video receivers, whether the video is amplitude or frequency modulated; 
and the present invention is particularly applicable to applications 
wherein it is desirable, or necessary, to minimize the combined bandwidth 
requirement of video and audio signals.