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OST Bulletin N0.60
Multichannel Television Sound Transmission and Audio
Processing Requirements for the BTSC System.
PREFACE
This bulletin contains those technical specifications for
the BTSC System as presented to the Federal Communications
Commission by the Electronics Industries Association. These
specifications are presented herein pursuant to the Report &
Order in BC Docket 21323 adopted March 29, 1984 and are
considered guidelines for stations employing the BTSC system of
multichannel sound transmission and audio processing.
The Commission in BC Docket 21323 has adopted very general
technical rules that will allow the television aural baseband to
be used for television stereophonic sound, second language
programming and any other broadcast or non-broadcast use.
The BTSC System uses a pilot subcarrier at 15,734 Hz. The
pilot allows receivers to recognize that transmissions are in
stereo and to switch into the stereophonic reception mode. To
ensure compatibility and to prevent BTSC type receivers from
falsely detecting other MTS formats, Docket 21323 restricts
emissions at 15,734 Hz. The purpose of this Bulletin is to
present the BTSC specifications which in accordance with FCC Rule
73.683(c)(3), are required to be met when a broadcast station
transmits an emission at 15,735 Hz.
A. Definitions 1
B. Transmission Standards 4
(a) Television Stereophonic Sound Standards 4
(b) Television Second Audio Program Standards 4
(c) Television Sound Encoding Standards 5
(d) Television Non-Program Related Aural Subcarrier
Standards 7
C. Transmission System Requirements/Multichannel Sound
Requirements 7
(a) Electrical Performance Standards for Stereophonic
Operation 7
(b) Electrical Performance Standards for Second Program
Operation 9
(c) Electrical Performance Standards for Video Transmission 10
(d) Electrical Performance Standards for Sound Encoding 11
D. Modulation Levels 12
Page 1
Standards for the BTSC system as presented to the Federal Communications
Commission by the Electronic Industries Association.
A. Definitions
Compandoring: A noise reduction process used in the stereophonic
subchannel and the second audio program subchannel consisting of
encoding (compression) before transmission and decoding (expansion)
after reception.
Composite stereophonic baseband signal:
The stereophonic sum modulating signal, the stereophonic difference
encoded signal and the pilot subcarrier.
Crosstalk: An undesired signal occuring in one channel caused by an
electrical signal in the other channels.
Decibel ERMS value: The exponentially time-weighted root mean
square (ERMS) value converted to dB as follows:
decibel ERMS value = 20 log
10 (ERMS value
______________
(Reference)
Where reference is the 0dB ERMS value.
Encoding: See Compandoring.
Equivalent input separation: A method of specifying the stereophonic
separation be referring variations from ideal at the output back to
the input. To accomplish this, an input signal which causes a non-
ideal output is varied by degrading input separation until the
output conforms to the ideal. The amount of input separation
degradation required is the equivalent input separation.
Equivalent modulation: See equivalent input tracking.
Equivalent input tracking: A method of specifying the tracking
ability of the encoding process by referring variations from the
ideal at the output back to the input of the encoder. To accomplish
this, an input signal which causes a non-ideal output is varied
until the output conforms to the ideal. The amount of input
variation required is the equivalent input tracking.
Page 2
Exponentially time-weighted root mean square (ERMS) value:
The ERMS value of a waveform is obtained from the following formula:
_____________________________________________
/ t
/ 1 /` 2 -(t-u)/T
/ --- / S (u)e du
\/ T /
`
-o~o
Where S(u) is the waveform in question, a function of time, T is the
exponential time-weighting period, and t is the time at which the
ERMS value is computed.
Incidental carrier phase modulation (ICPM):
Angle modulation of the visual carrier by video signal components
which, when detected in TV receiver intercarrier circuits, cause an
audio interference known as intercarrier buzz.
Left (or right) audio signal:
The electrical output of a microphone or combination of microphones
placed so as to convey the intensity, time, and location of sounds
originating predominately to the listner's left (L) (or right (R))
of the center of the performing area.
Left (or right) stereophonic channel:
The transmission path for the left (or right) audio path.
Main Channel:
The band of frequencies from 50 to 15,000 Hz which frequency
modulates the aural carrier.
Multichannel sound:
Multiplex transmission on the TV aural carrier.
Multiplex transmission:
The simultaneous transmission of the TV program main channel audio
signal and one or more subchannel signals. The subchannels include
a stereophonic subchannel, a second audio program subchannel, a non-
program related subchannel and a pilot subcarrier.*
Non-program related subchannel:
The subchannel for the multiplex transmission of a frequency-
modulated subcarrier for telemetry or other purposes.
Pilot subcarrier:
A subcarrier serving as the control signal for use in the reception
of stereophonic TV sound broadcasts.
* FCC NOTE: The Commission does not require nor restrict the use of the
second audio program subchannel or the non-program related subchannel.
Page 3
Second Audio Program (SAP) broadcast:
The multiplex transmission of a second audio program utilizing the
second audio program subchannel.
Second Audio Program (SAP) subchannel:
The channel containing the frequency-modulated second audio program
subcarrier.
Second program audio signal:
The monophonic audio signal delivered to the SAP encoder.
Second program encoded signal:
The second program audio signal after encoding.
75 microsecond(75us) equivalent modulation:
The audio signal level prior to encoding that results in a stated
percentage of modulation when the encoding process is replaced by
75us pre-emphasis.
Spectral compression:
A process wherein variations in spectral content of an audio signal
are reduced by varying a frequency filtering function applied to the
signal in response to the spectral content of the signal.
Stereophonic difference audio signal:
The left audio signal minus the right audio signal (L-R).
Stereophonic difference encoded signal:
The stereophonic difference audio signal after encoding.
Stereophonic separation:
The ratio of the electrical signal caused in the right (or left)
stereophonic channel to the electrical signal caused in the left (or
right) stereophonic channel by the transmission of only a right (or
left) signal.
Stereophonic sum audio signal:
The left audio signal plus the right audio signal (L+R).
Stereophonic sum channel compensation:
A process wherin the phase and amplitude response resulting from
bandlimiting in the process of encoding the stereophonic difference
audio signal (which, if uncompensated, would detrimentaly affect
stereo separation) is compensated by an identical phase and
amplitude response applied to the stereophonic sum audio signal.
page 4
Stereophonic sum modulating signal:
The stereophonic sum audio signal after compensation, pre-emphasis
and other processing.
Stereophonic subcarrier:
A subcarrier having a frequency which is the second harmonic of the
pilot subcarrier frequency and which is employed in TV stereophonic
sound broadcasting.
Stereophonic subchannel:
The subchannel containing the sterophonic subcarrier and its
associated sidebands.
Wideband amplitude compression:
A process wherein the dynamic range of an audio signal is compressed
by simultaneously varying the gain of all audio frequencies equally.
B. Transmission Standards
(a) Television stereophonic sound standards.
(1) Television broadcast stations may transmit stereophonic
sound by employing a subcarrier on the aural carrier.
The main channel modulating signal shall be the
stereophonic sum modulating signal; the subcarrier
modulation shall be the stereophonic difference encoded
signal.
(2) The subcarrier shall be the second harmonic of a pilot
signal which is transmitted at a frequency equal to the
horizontal line rate. Note: If the station is engaged
in stereophonic sound transmission accompanied by
monochrome picture transmission, the horizontal
scanning frequency shall be 15,734 Hz +/- 2Hz.
(3) The subcarrier shall be double sideband amplitude
modulated with a suppressed carrier and shall be capable
of accepting a stereophonic difference encoded signal
over a range of 50 - 15,000 Hz.
(4) The total modulation of the aural carrier, including
that caused by all sucarriers, shall comply with the
requirements of 73.1570 of the FCC Rules and
Regulations.
(b) Television second audio program standards.
(1) Television broadcast stations may transmit a subcarrier
carrying a second audio program.
(2) The subcarrier frequency shall nominally be equal to the
fifth harmonic of the horizontal line rate.
Page 5
(3) The second program encoded signal shall frequency
modulate the subcarrier to a peak deviation of +/- 10
kHz.
(4) The second audio program subchannel shall be capable of
accepting second program encoded signals over a range of
50 - 10,000 Hz.
(5) The modulation of the aural carrier by the second audio
program subcarrier shall comply with (D)(a)(1)(iv) of
this bulletin (+/- 15 kHz deviation).
(c) Television sound encoding standards.
(1) The stereophonic difference audio signal and the second
program audio signal shall be encoded prior to
modulating their respective subcarriers.*
(2) This encoding shall have the following characteristics,
where f is expressed in kilohertz (kHz).
(i) Fixed pre-emphasis (F(f)) whose transfer function
is as follows:
F(f) = (jf/0.408)+1 (jf/2.19)+1
____________ x ____________
(jf/5.23)+1 (jf/62.5)+1
(ii) Wideband amplitude compression wherein:
(a) The decibel gain (or loss) applied to the
audio signal during encoding is equal to minus
one times the decibel ERMS value of the
encoded signal (the result of the encoding
process), weighted by a transfer function
(P(f)) as follows:
P(f) = (jf/0.0354)
______________________________
((jf/0.0354)+1) ((jf/2.09)+1)
(b) The exponential time weighting period T
1
of the ERMS detector referred to above in (a)
is 34.7 ms.
(c) The zero decibel reference ERMS value for the
encoded signal referred to above in (a) is
8.99% modulation of the subcarrier at 0.300
kHz.
* FCC NOTE: When the SAP channel is used for non-program related audio
signals, encoding is not specified.
Page 6
(iii) Spectral compression wherein:
(a) The transfer function S(f,b) applied to the audio
signal during encoding is:
D/20
S(f,b) = 1+ (jf/F) (b+51)/(b+1) , where b=-10
______________________
1+(jf/F) (1+51b)/(b+1)
F=20.1 kHz; D=decibel rms value and b is the
decibel ERMS value of the encoded signal (the
result of the encoding process) weighted according
to a frequency transfer function Q (f) as follows:
3
Q(f)= (jf/5.86)
________________________________________________________
2
((jf/7.66) +(jf/7.31)+1) x ((jf/26.9)+1) x ((jf/3.92)+1)
(b) The exponential time waiting period T of the
2
ERMS detector referred to above in (iii-a) is
11.4 rms.
(c) The ERMS zero decibel reference for the encoded
signal referred to above in (iii-a) is 5.16%
modulation of the subcarrier at 8 kHz.
Note: This reference results in a +18.4 dB gain
through the encoding process at 32.0% modulation
using a 8 kHz tone, when the output bandlimiting
filter (see (iv) and (v) following) gain is +18.4
dB at 8 kHz.
(iv) Overmodulation protection which functionally follows the
functions i,ii, & iii above.
(v) Bandlimiting to appropriately restrict bandwidth which
functionally follows the functions i, ii, & iii above.
Page 7
(d) Television non-program related aural subcarrier standards.
(1) Multiplexing of the aural carrier is subject to the
requirements of Section 73.682(c) of the FCC Rules and
Regulations; provided, however, that when the stereophonic
and/or second audio program subchannels are transmitted,
mulitplexing of the aural carrier by non-program related
subchannels is subject to the following changes:
(i) The maximum modulation of the aural carrier by the
non-program related subcarrier shall comply with
the requirements of (D)(a)(1(vi) of this bulletin.
(ii) When the stereophonic and second audio program
subcarriers are transmitted, the instantaneous
frequency of the non-program related subcarrier
shall have the average value of six and one-half
times the frequency of the horizontal scanning
frequency with a tolerance of +/- 500 Hz.
(iii) When only the stereophonic subcarrier is
transmitted, the instantaneous frequency of the
non-program related subcarrier shall lie between 47
and 120 kHz with a tolerance of +/- 500 Hz.
(C) Transmission system requirements/Multichannel sound requirements 1/
(a) Electrical performance standards for stereophonic operation.
(1) The aural transmitter must operate satisfactorily with a
frequency deviation of +/- 73 kHz.
It is recommended that the transmitter operate
satisfactorily with a frequency deviation of +/- 100 kHz.
(2) The pilot subcarrier shall be frequency locked to the
horizontal scanning frequency of the transmitted video
signal.
(3) The requirements of section 73.687(b)(2) of the FCC Rules
and Regulations shall be complied with for both the (L+R)
main channel and (L-R) subchannel, except for pre-emphasis
as specified in Section (B)(c) of this bulletin, with the
additional requirement that the aural transmitter shall be
capable of transmitting a band of frequencies from 50 to
120,000 Hz.
1/ Unless otherwise specified, the transmission system requirements are
defined for 75us pre-emphasis (which is matched to that in the main channel in
the case of stereophonic transmission) substituted for encoding. Measurements
are made over the band of 50 to 15,000 Hz and employ 75us de-emphasis in the
measuring equipment.
Page 8
(4) The sterophonic subcarrier, being the second harmonic of
the pilot signal, shall cross the time axis with a
positive slope simultaneously with each crossing of the
time axis by the pilot subcarrier. The pilot subcarrier
shall cross the time axis at points located within +/- 3
degrees (approximately +/- 0.53 microseconds) of the zero
crossings of the stereophonic subcarrier.
(5) The unmodulated stereophonic subcarrier shall be
suppressed to a level less than 0.25 kHz deviation of the
main carrier.
(6) The combined audio frequency harmonics measured at the
output of the transmitting system (including the sound
encoder), as defined in 73.687 (b) (3) of the FCC Rules
and Regulation, at any audio frequency from 50 - 15,000 Hz
and at modulating percentages of 25, 50 and 100%, 75us
equivalent modulation shall not exceed the rms values in
the following table:
50 to 100 Hz 3.5%
100 to 7,500 Hz 2.5%
7,500 to 15,000 Hz 3.0%
Harmonics shall be included to 30 kHz.
(7) The ratio of peak main channel deviation to the peak
stereophonic subchannel deviation when only a steady state
left (or right) signal exists shall nominally be one half
for all levels of this signal and for all frequencies from
50 - 15,000 Hz.
(8) The phase and amplitude characteristics of the
stereophonic sum modulating signal and the stereophonic
difference encoded signal shall be such that the minimum
equivalent input separation at 10%, 75us equivalent
modulation is as follows:
(i) 30 dB separation from 100 Hz to 8 kHz.
(ii) Smoothly decreasing separation below 100 Hz,
from 30 dB to 26 dB at 50 Hz.
(iii) Smoothly decreasing separation above 8 kHz,
from 30 dB to 20 dB at 15 kHz.
Page 9
Note: It is recommended that the transmission system, excluding
encoding, shall meet a 40 dB separation requirement when 75us pre-
emphasis is substituted for sound encoding.
(9) Crosstalk into the main channel caused by a signal in the
stereophonic subchannel shall be at least 40 dB below 25 kHz main
carrier deviation.
(10) Crosstalk into the main channel caused by a non-stereophonic
multiplex signal shall be at least 60 dB below 25 kHz aural carrier
deviation.
(11) Crosstalk into the stereophonic subchannel caused by a signal in the
main channel shall be at least 40 dB below 50 kHz aural carrier
deviation.
(12) Crosstalk into the stereophonic subchannel caused by another
multiplex signal shall be at least 60 dB below 50 kHz aural carrier
deviation.
(13) The aural transmitting system output frequency modulation noise
level in band of 50 to 15,000 Hz (with de-emphasis) must be at least
58 dB below the audio level representing a frequency deviation of
+/- 25 kHz. The frequency modulation noise level in the
stereophonic subchannel, after demodulation, in the band of 50 to
15,000 Hz (with de-emphasis) must be at least 55 dB below the audio
level representing a frequency deviation of +/- 50 kHz.
(14) The pilot subcarrier-to-interference ration, over a bandwidth of 1
kHz centered at the pilot subcarrier, shall be at least 40 dB.
(b) Electrical performance standards for second audio program operation
(1) The aural transmitter frequency deviation capability must comply
with the requirements of Section C(a)(1) of this bulletin.
(2) The aural transmitter modulation bandwidth capability shall comply
with the requirements of C(a)(3) of this bulletin.
(3) The unmodulated subcarrier shall be frequency locked to the fifth
harmonic of horizontal line rate. When modulated, the center shall
nominally be that of the fifth harmonic of the horizontal line
scanning frequency with a tolerance of +/- 500 Hz.
(4) Frequency modulation of the subcarrier shall be used.
(5) The subcarrier shall be shut off when the second audio program
subchannel is not in use.
Page 10
(6) The combined audio frequency harmonics measured at the output of the
transmitting system (including the encoder) at any audio frequency
from 50 to 10,000 Hz and at the modulating percentages of 25, 50 and
100% 75us equivalent modulation shall not exceed the rms values in
the following table.
50 to 100 Hz 3.5%
100 to 5,000 Hz 4.0%
5,000 to 10,000 Hz 3.0%
Harmonics shall be included to 20 kHz.
(7) Crosstalk into the SAP subchannel caused by a signal in the main
channel and/or the stereophonic subchannel shall be at least 50 dB
below the level representing full modulation of the SAP subchannel
(+/- 10 kHz deviation).
(8) The aural transmitting system output frequency modulation noise
level after subcarrier demodulation must be at least 50 dB below the
level representing full modulation of the SAP subcarrier (+/- 10 kHz
deviation).
(9) The aural transmitting system output amplitude modulation noise
level in the band of 63,000-94,000 Hz shall be at least 50 dB below
the level representing 100% amplitude modulation.
(c) Electrical performance standards for video transmission.
(1) The requirements of 73.687 (a) (1) and (2) of the FCC Rules and
Regulations shall be complied with; provided, however, that when the
station is engaged in stereophonic sound transmission, or when the
station transmits stereophonic sound and/or second audio program,
subparagraphs (1) and (2) apply, except as modified by the
following: A sine wave of 4.5 MHz introduced at the terminals of
the transmitter which are normally fed the composite color picture
signal shall produce a radiated signal having an amplitude (as
measured with a diode on the RF transmission line supplying power to
the antenna after the combination of visual and aural power) which
is down at least 30 dB with respect to the signal produced by a sine
wave of 200 kHz.
(2) In the situation where stereophonic sound and/or a second audio
program is transmitted, the following requirements shall be met:
the incidental phase modulation of the visual carrier by video
signals in the frequency band between 1 and 92 kHz shall be less
than three degrees for carrier amplitude below 0.75 of the voltage
at synchronizing peaks and less than 5 degrees for carrier
amplitudes exceeding 0.75 of the voltage at synchronizing peaks.
(d) Electrical performance standards for sound encoding.
Page 11
(1) The equivalent input noise of the sound encoder, measured over
a 15 kHz bandwidth, shall be more than 70 dB below the 100 Hz,
100% 75us equivalent modulation level.
(2) The tracking characteristics of the sound encoder shall be such
that the minimum equivalent input separation at modulation
percentages from 1% to 100% 75us equivalent modulation is 26 dB
from 100 Hz to 8 kHz.
D. Modulation Level
(a) When only a monophonic audio signal is transmitted, the
modulation of the aural carrier shall not exceed 25 kHz
deviation on peaks of frequent recurrence, unless some other
peak modulation level is specified.
(b) For stations transmitting more than one audio program channel
the maximum modulation levels must meet the following
limitations:
(1) TV stations transmitting stereophonic sound signals must
limit the modulation of the audio carrier by the
stereophonic sum modulating signal to 25 kHz deviation on
peaks of frequent recurrence.
(2) TV stations transmitting stereophonic sound signals must
limit the modulation of the audio carrier by the
stereophonic sum modulating signal and stereophonic
difference encoded signal to 50 kHz deviation on peaks of
frequent reccurence.
(3) The modulation of the aural carrier by the stereophonic
pilot signal shall be 5.0 kHz deviation with a tolerance
of +/- 0.5 kHz.
(4) TV stations transmitting a second audio program must limit
the modulation of the aural carrier by the SAP subcarrier
to 15 kHz deviation.
(5) TV stations transmitting multiplex signals on the aural
carrier for non-program related purposes must limit the
modulation of the aural carrier by the arithmetic sum of
all subcarriers, other than the stereophonic and second
audio program, to 3 kHz deviation.
(6) Total modulation of the aural carrier by multichannel
sound shall not exceed 73 kHz.