squelch works like a noise gate: it replaces an incoming PCM signal with digital silence when it's been sufficiently quiet for a sufficient time.
The input is assumed to be raw 16-bit signed-integer PCM. The signal comes in through stdin and the output signal is written to stdout.
The program treats the signal as a single channel, but it should work okay for stereo and IQ as well. It won't work correctly with 8-bit input though.
- C++11 compiler
- GNU make
make
some_program --producing --samples | squelch [OPTION]... | ...
All options are optional and have somewhat reasonable defaults.
| Long option | Short option | Default | Description |
|---|---|---|---|
--amplitude-limit-db |
-L |
-30 | Silence threshold in dBFS. The input must stay below this to get squelched. |
--amplitude-limit-abs |
-l |
1024 (-30 dBFS) | Same as -L, but in absolute (semi-)amplitude. You can provide one or the other. |
--silence-duration |
-d |
4096 | The signal gets muted when this many successive samples are below the silence threshold. Unmuting will happen even if a single sample gets above the limit. |
--fade-time |
-t |
512 | Transition time, in samples. This is how long it takes to smoothly fade the signal out after --silence-duration has passed; and how long it takes to fade back in after the first sign of signal.Use 0 to disable fading; it'll just instantly switch with a 'snap'. |
--buffer-length |
-u |
2048 | I/O buffer length, in samples. This can be used to control the frequency of output flushing, to fine-tune performance. It doesn't affect the output samples or squelch behavior in any way. |
$ git rev-parse HEAD && cat /sys/firmware/devicetree/base/model
293ff5023afe4d96442641ada6226de5728512e9
Raspberry Pi 3 Model B Plus Rev 1.3
$ pv -k -S -s 1000M -F "%{average-rate}" < /dev/random | ./build/squelch > /dev/null
(88.9MB/s)
$ pv -k -S -s 1000M -F "%{average-rate}" < /dev/zero | ./build/squelch > /dev/null
( 197MB/s)
$ # RasPi 3B+:
$ # From /dev/random: 44 Msps single-channel
$ # From /dev/zero: 98 Msps single-channel
$ git rev-parse HEAD && sysctl hw.model
293ff5023afe4d96442641ada6226de5728512e9
hw.model: MacBookPro18,3
$ pv -k -S -s 1000M -F "%{average-rate}" < /dev/random | ./build/squelch --buffer-length 65536 > /dev/null
( 373MB/s)
$ pv -k -S -s 1000M -F "%{average-rate}" < /dev/zero | ./build/squelch --buffer-length 65536 > /dev/null
(1.57GB/s)
$ # Apple M1:
$ # From /dev/random: 186 Msps single-channel
$ # From /dev/zero: 785 Msps single-channel