[FFmpeg-trac] #10345(undetermined:new): Multiplex Filter (or codec)

[FFmpeg]

#10345: Multiplex Filter (or codec)
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             Reporter:  Noitarud     |                    Owner:  (none)
                 Type:  enhancement  |                   Status:  new
             Priority:  normal       |                Component:
                                     |  undetermined
              Version:  unspecified  |               Resolution:
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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Comment (by Noitarud):

 There is this:
 https://en.m.wikipedia.org/wiki/FM_broadcasting#Stereo_FM
 It is important that stereo broadcasts be compatible with mono receivers.
 For this reason, the left (L) and right (R) channels are algebraically
 encoded into sum (L+R) and difference (L−R) signals. A mono receiver will
 use just the L+R signal so the listener will hear both channels through
 the single loudspeaker.
 The (L+R) signal is limited to 30 Hz to 15 kHz to protect a 19 kHz pilot
 signal. The (L−R) signal, which is also limited to 15 kHz, is amplitude
 modulated onto a 38 kHz double-sideband suppressed-carrier (DSB-SC)
 signal, thus occupying 23 kHz to 53 kHz. A 19 kHz ± 2 Hz[12] pilot tone,
 at exactly half the 38 kHz sub-carrier frequency and with a precise phase
 relationship to it,…is also generated. The pilot is transmitted at 8–10%
 of overall modulation level and used by the receiver to identify a stereo
 transmission and to regenerate the 38 kHz sub-carrier with the correct
 phase. The composite stereo multiplex signal contains the Main Channel
 (L+R), the pilot tone, and the (L−R) difference signal. …Another way to
 look at the resulting signal is that it alternates between left and right
 at 38 kHz, with the phase determined by the 19 kHz pilot signal.

 https://en.m.wikipedia.org/wiki/FM_broadcasting#Quadraphonic_FM
 There are two additional subcarriers in the Quadraplex system,
 supplementing the single one used in standard stereo FM. The baseband
 layout is as follows:

 50 Hz to 15 kHz main channel (sum of all 4 channels) (LF+LR+RF+RR) signal,
 for mono FM listening compatibility.
 23 to 53 kHz (sine quadrature subcarrier) (LF+LR) − (RF+RR) left minus
 right difference signal. This signal's modulation in algebraic sum and
 difference with the main channel is used for 2 channel stereo listener
 compatibility.
 23 to 53 kHz (cosine quadrature 38 kHz subcarrier) (LF+RR) − (LR+RF)
 Diagonal difference. This signal's modulation in algebraic sum and
 difference with the main channel and all the other subcarriers is used for
 the Quadraphonic listener.
 61 to 91 kHz (sine quadrature 76 kHz subcarrier) (LF+RF) − (LR+RR) Front-
 back difference. This signal's modulation in algebraic sum and difference
 with the main channel and all the other subcarriers is also used for the
 Quadraphonic listener.
 105 kHz SCA subcarrier, phase-locked to 19 kHz pilot, for reading services
 for the blind, background music, etc.
 The normal stereo signal can be considered as switching between left and
 right channels at 38 kHz, appropriately band-limited. The quadraphonic
 signal can be considered as cycling through LF, LR, RF, RR, at 76 kHz.[20]
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/10345#comment:6>
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