[pulseaudio-discuss] audio noise using module-loopback

[golden]

Hi all,

    Recently I have found a noise problem when using module-loopback.
    I connected a alsa-source to a alsa-sink with module-loopback
    the data from alsa-source is actually sine-wave (rate=44100, 
format=s16le, channels=2)

    I found that in the adjust_rates function, if I comment 
"pa_sink_input_set_rate",
    there is no noise, but if I uncomment "pa_sink_input_set_rate", 
problem appears.

    Here is the setup log:

     D/NMAudio ( 1797): [tid=1816] D: Negotiated format: pcm, 
format.sample_format = "\"s16le\""  format.rate = "44100" format.channels ="
D/NMAudio ( 1797): [tid=1816] D: Resampler:
D/NMAudio ( 1797): [tid=1816] D:   rate 44100 -> 44100 (method trivial)
D/NMAudio ( 1797): [tid=1816] D: i_ss.format=s16le, o_ss.format=s16le
D/NMAudio ( 1797): [tid=1816] D:   format s16le -> s16le (intermediate 
s16le)
D/NMAudio ( 1797): [tid=1816] D:   channels 2 -> 2 (resampling 2)
D/NMAudio ( 1797): [tid=1816] D: memblockq requested: 
maxlength=33554432, tlength=0, base=4, prebuf=0, minreq=1 maxrewind=0
D/NMAudio ( 1797): [tid=1816] D: memblockq sanitized: 
maxlength=33554432, tlength=33554432, base=4, prebuf=0, minreq=4 maxrewind=0
I/NMAudio ( 1797): [tid=1816] I: Created input 2 "(null)" on audioio.22 
with sample spec s16le 2ch 44100Hz and channel map front-leftt
I/NMAudio ( 1797): [tid=1816] I:     media.role = "abstract"
D/NMAudio ( 1797): [tid=1816] D: Negotiated format: pcm, 
format.sample_format = "\"s16le\""  format.rate = "44100" format.channels ="
D/NMAudio ( 1797): [tid=1816] D: memblockq requested: 
maxlength=33554432, tlength=0, base=4, prebuf=0, minreq=1 maxrewind=0
D/NMAudio ( 1797): [tid=1816] D: memblockq sanitized: 
maxlength=33554432, tlength=33554432, base=4, prebuf=0, minreq=4 maxrewind=0
I/NMAudio ( 1797): [tid=1816] I: Created output 2 "(null)" on audioio.17 
with sample spec s16le 2ch 44100Hz and channel map front-left
I/NMAudio ( 1797): [tid=1816] I:     media.role = "abstract"
D/NMAudio ( 1797): [tid=1816] D: memblockq requested: 
maxlength=33554432, tlength=33554432, base=4, prebuf=0, minreq=0 maxrewind=0
D/NMAudio ( 1797): [tid=1816] D: memblockq sanitized: 
maxlength=33554432, tlength=33554432, base=4, prebuf=0, minreq=4 maxrewind=0
I/NMAudio ( 1797): [tid=1816] I: Adding 35280 bytes of silence to queue
I/NMAudio ( 1797): [tid=1844] I: Max request changed
D/NMAudio ( 1797): [tid=1844] D: Requesting rewind due to uncorking
D/NMAudio ( 1797): [tid=1844] D: Requested to rewind 5292 bytes.
D/NMAudio ( 1797): [tid=1844] D: Processing rewind...
D/NMAudio ( 1797): [tid=1844] D: Processing rewind...
D/NMAudio ( 1797): [tid=1844] D: Rewound 4140 bytes.
I/NMAudio ( 1797): [tid=1816] I: Loaded "module-loopback" (index: #7; 
argument: "loopbackid=1722 source=audioio.17 sink=audioio.22

-----------> before this line, the rate of sink-input was not adjusted, 
everything is fine, no noise appears

D/NMAudio ( 1797): [tid=1816] D: Loopback overall latency is 19.46 ms + 
182.97 ms + 2.67 ms = 205.02 ms (at the base rate: 205.02 ms,)
D/NMAudio ( 1797): [tid=1816] D: Latency difference: 5.02 �± 1.00 ms, 
rate difference: 0 Hz
D/NMAudio ( 1797): [tid=1816] D: [audioio.22] Updated sampling rate to 
44200 Hz.

-----------> after 10 second, the rate of sink-input was adjusted, noise 
comes out.

    I have been playing around all the new rate variables, any value 
that do not equals to 44100 will make audio noise.

    That looks very strange to me, so I`m asking if anyone have met this 
problem before ?

    Thanks !




BR,
Lixin