(Pertaining to Part 3 of FCC Regulations-Radio Broadcast Services) - Filed April 24, 1961.

1. New Section 3.297 is added to read as follows : 3.297 Sterephonic Broadcasting.

FM broadcast stations may, without further authority, transmit stereophonic programs in accordance with the technical standards set forth in 3.322: Provided, however, That the Commission and the Engineer in Charge of the radio district in which the station is located shall be notified within 10 days from the installation of type-accepted stereophonic transmission equipment or any change therein, and: Provided further, that the Commission and the Engineer in Charge shall be notified within 10 days from the commencement of stereophonic operation, scheduled hours of such operation or any change therein.

2. Section 3.310 is amended by adding the following paragraphs:
3.310 Definitions.
(t) Cross-talk. An undesired signal occurring in one channel caused by an electrical signal in another channel.
(u) FM stereophonic broadcast. The transmission of a stereophonic program by a single FM broadcast station utilizing the main channel and a stereophonic subchannel.
(v) Left (or right) 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 listener's left (or right) of the center of the performing area.
(w) Left (or right) stereophonic channel. The left (or right) signal as electrically reproduced in reception of FM stereophonic broadcasts.
(x)Main channel. The band of frequencies from 50 to 15,000 cycles which frequency modulate the main carrier.
(y) Pilot sttbearricr. A subcarrier serving as a control signal for use in the reception of FM stereophonic broadcasts.
(z) 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.
(aa) Stereophonic subcarrier. A subcarrier having a frequency which is the second harmonic of the pilot subcarrier frequency and which is employed in FM stereophonic broadcasting.
(bb) Stereophonic subchannel. The band of frequencies from 23 to 53 kilocycles containing the stereophonic subcarrier and its associated sidebands.

3. Section 3.319 is amended to read as follows: 3.319 Subsidiary Communications Multiplex
Operations: Engineering Standards.
(a) Frequency modulation of SCA sub-carriers shall be used.
(b) The instantaneous frequency of SCA subcarriers shall at all times be within the range of 20 to 75 kilocycles: Provided, however, That when the station is engaged in stereophonic broadcasting pursuant to 3.297, the instantaneous frequency of SCA subcarriers shall at all times be within the range 53 to 75 kilocycles.
(c) The arithmetic sum of the modulation of the main carrier by SCA subcarriers shall not exceed 30 per cent: Provided, however, That when the station is engaged in stereophonic broadcasting pursuant to 3.297, the arithmetic sum of the modulation of the main carrier by the SCA subcarriers shall not exceed 10 per cent.
NOTE: Inasmuch as presently approved FM modulation monitors have been designed to meet requirements for modulation frequencies of from 50 to 15,000 cycles, the use of such monitors for reading the modulation percentages during SCA multiplex operation may not be appropriate since the subcarriers utilized are above 20.000 cycles.
(d) The total modulation of the main carrier, including SCA subcarriers, shall meet the requirements of 3.268.
(e) Frequency modulation of the main carrier caused by the SCA subcarrier operation shall, in the frequency range 50 to 15,000 cycles, be at least 60 db below 100 per cent modulation: Provided, however, That when the station is engaged in stereophonic broadcasting pursuant to 3.297, frequency modulation of the main carrier by the SCA subcarrier operation shall, in the frequency range 50 to 53,000 cycles, be at least 60 db below 100 percent modulation.

4. New Section 3.322 is added to read as follows : 3.322 Stereophonic Transmission Standards.
(a) The modulating signal for the main channel shall consist of the sum of the left and right signals.
(b) A pilot subcarrier at 19,000 cycles plus or minus 2 cycles shall be transmitted that shall frequency modulate the main carrier between the limits of 8 and 10 per cent.
(c) The stereophonic subcarrier shall be the second harmonic of the pilot subcarrier and shall cross the time axis with a positive slope simultaneously with each crossing of the time axis by the pilot subcarrier.
(d) Amplitude modulation of the stereophonic subcarrier shall be used.
(e) The stereophonic subcarrier shall be suppressed to a level less than one per cent modulation of the main carrier.
(f) The stereophonic subcarrier shall be capable of accepting audio frequencies from 50 to 15,000 cycles.
(g) The modulating signal for the stereophonic subcarrier shall be equal to the difference of the left and right signals.
(h) The pre-emphasis characteristics of the stereophonic subchannel shall be identical with those of the main channel with respect to phase and amplitude at all frequencies.
(i) The sum of the side bands resulting from amplitude modulation of the stereophonic subcarrier shall not cause a peak deviation of the main carrier in excess of 45 per cent of total modulation (excluding SCA subcarriers) when only a left (or right) signal exists; simultaneously in the main channel, the deviation when only a left (or right) signal exists shall not exceed 45 per cent of total modulation (excluding SCA subcarriers).
(j) Total modulation of the main carrier including pilot subcarrier and SCA sub-carriers shall meet the requirements of Section 3.268 with maximum modulation of the main carrier by all SCA subcarriers limited to 10 per cent.
(k) At the instant when only a positive left signal is applied, the main channel modulation shall cause an upward deviation of the main carrier frequency; and the stereophonic subcarrier and its sidebands signal shall cross the time axis simultaneously and in the same direction.
(1) The ratio of peak main channel deviation to peak stereophonic subchannel deviation when only a steady state left (or right) signal exists shall be within plus or minus 3.5 per cent of unity for all levels of this signal and all frequencies from 50 to 15,000 cycles.
(m) The phase difference between the zero points of the main channel signal and the stereophonic subcarrier sidebands envelope, when only a steady state left (or right) signal exists, shall not exceed plus or minus 3 degrees for audio modulating frequencies from 50 to 15,000 cycles.
NOTE: If the stereophonic separation between left and right stereophonic channels is better than 29.7 decibels at audio modulating frequencies between 50 and 15,000 cycles, it will be assumed that paragraphs (1) and (m) of this section have been complied with.
(n) Cross-talk into the main channel caused by a signal in the stereophonic subchannel shall be attenuated at least 40 decibels below 90 per cent modulation.
(o) Cross-talk into the stereophonic subchannel caused by a signal in the main channel shall be attenuated at least 40 decibels below 90 per cent modulation.
(p) For required transmitter performance, all of the requirements of Section 3.254 shall apply with the exception that the maximum modulation to be employed is 90 per cent (excluding pilot subcarrier) rather than 100 per cent.
(q) For electrical performance standards of the transmitter and associated equipment, the requirements of Section 3.317 (a) (2), (3), (4) and (5) shall apply to the main channel and stereophonic subc lannel alike, except that where 100 per cen: modulation is referred to, this figure shall include the pilot subcarrier.