[pulseaudio-discuss] can rewindings in the null sink produce noises in programs recording its monitor?

[Tanu Kaskinen]

On Sat, 2018-10-06 at 15:29 -0300, wellington wallace wrote:
> Hi! PulseEffects developer here again.
> 
> Like the title says I'd like to know if rewinds can cause crackling noises
> when we are recording from a null sink monitor.

Yes it can: 
https://gitlab.freedesktop.org/pulseaudio/pulseaudio/issues/304

> In PulseEffecs I use the
> plugin pulsesrc from GStreamer to record the null sink monitor and whenever
> there is a change in the null sink volume or in the volume of a sink input
> playing to the null sink I can here noises. Looking at Pulseaudio's logs I
> can see lines with:
> 
> [null-sink] module-null-sink.c: Requested to rewind 3528 bytes.
> [null-sink] sink.c: Processing rewind...
> [null-sink] sink-input.c: Have to rewind 2840 bytes on render memblockq.
> [null-sink] sink-input.c: Have to rewind 1420 bytes on implementor.
> [null-sink] source.c: Processing rewind...
> [null-sink] module-null-sink.c: Rewound 2840 bytes.
> [pulseaudio] module-stream-restore.c: Storing volume/mute/device for stream
> sink-input-by-media-role:music.
> [pulseaudio] protocol-native.c: Client spotify changes volume of sink input
> Spotify.
> 
> whenever the application volume is changed. At the same time they are shown
> I can hear cracklings. So it seems related. I noticed that forcing pulsesrc
> to use lower latencies help but do not fix the problem. Changing volumes
> with pulsesrc latency-time parameter set to 1000 us produces less noises
> than when it is set to 10000 us.
> 
> I tried my best to see if there is anything I can do on my side to remove
> this noise I found nothing. Is that how things are or is there anything
> that can be done to remove this noises?

This is how things are. It would be great if someone would have a hard
look at the monitor source rewinding code and see what goes wrong
there.

-- 
Tanu

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