On 19.02.2018 16:56, Raman Shishniou wrote: > Hello, > > Currently a loopback module does a double resampling if the source > and sink sample rates are different. > > I used a simple config to test it: > load-module module-null-source source_name=src rate=48000 > load-module module-null-sink sink_name=dst rate=96000 > load-module module-loopback source=src sink=dst > > After start I see in logs: > D: [pulseaudio] module-loopback.c: Loopback overall latency is 56.14 ms + 67.48 ms + 53.20 ms = 176.76 ms > D: [pulseaudio] module-loopback.c: Loopback latency at base rate is 176.46 ms > D: [pulseaudio] module-loopback.c: [dst] Updated sampling rate to 95758 Hz. > D: [pulseaudio] module-loopback.c: Loopback overall latency is 23.17 ms + 134.20 ms + 44.60 ms = 201.94 ms > D: [pulseaudio] module-loopback.c: Loopback latency at base rate is 201.60 ms > D: [pulseaudio] module-loopback.c: [dst] Updated sampling rate to 95925 Hz. > D: [pulseaudio] module-loopback.c: Loopback overall latency is 44.15 ms + 133.80 ms + 31.56 ms = 209.48 ms > D: [pulseaudio] module-loopback.c: Loopback latency at base rate is 209.37 ms > D: [pulseaudio] module-loopback.c: [dst] Updated sampling rate to 95994 Hz. > > Sink-inputs and source-outputs: > $ ~/bin/pactl list short source-outputs > 0 0 - module-loopback.c s16le 2ch 96000Hz > $ ~/bin/pactl list short sink-inputs > 0 0 - module-loopback.c s16le 2ch 95994Hz > > I.e. first resample occurs in source-output (48000Hz -> 96000Hz) and > the second in sink-input (95994Hz -> 96000Hz). > > I think it should change source-output's sample rate during latency recalculations. > In this case there should be only one real resampler. This should increase > audio quality and reduce cpu usage. > You can specify a sample-rate for module-loopback. So if you do the same as above, but with rate=48000, the first re-sampling will not happen. If you don't specify a rate, module-loopback uses the rate of the sink. But you are right, because we do re-sampling on the sink-input side anyway, it would probably make more sense to use the source rate as default. This can easily be fixed in the module init function. Will you send a patch?
