[pulseaudio-tickets] [Bug 83557] New: module-echo-cancel: should reduce noise even if nothing is being played

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=83557

          Priority: medium
            Bug ID: 83557
                CC: lennart at poettering.net
          Assignee: pulseaudio-bugs at lists.freedesktop.org
           Summary: module-echo-cancel: should reduce noise even if
                    nothing is being played
        QA Contact: pulseaudio-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: All
          Reporter: patrakov at gmail.com
          Hardware: Other
            Status: NEW
           Version: unspecified
         Component: modules
           Product: PulseAudio

module-echo-cancel, surprisingly, not only does echo cancellation, but also
other useful effects, like automatic gain control and noise reduction. However,
these effects are only applied when something is being played through the
echo-cancelled sink. I think this is wrong: these effects should be always
applied, because they are useful for voice-recorder applications.

To demonstrate the bug:

1. Load the module:

pacmd load-module module-echo-cancel

In my case, it attaches to the analog output of my onboard soundcard and to my
webcam's microphone.

2. Copy (for monitoring purposes) the output of the echo canceller to the
headphones, in a way that the echo canceller does not see this loopback:

pacat --record --device
alsa_input.usb-046d_0821_39BD2FC0-00-U0x46d0x821.analog-stereo.echo-cancel |
pacat --playback --device alsa_output.pci-0000_00_1b.0.analog-stereo

At this point, you should hear room noise and microphone hiss. The same hiss
would be recorded if you use parec to record the sound into a wav file.

Microphone hiss is exactly this bug.

3. Now open a new terminal and play silence through the echo canceller:

pacat --playback --device
alsa_output.pci-0000_00_1b.0.analog-stereo.echo-cancel /dev/zero

Result: no more microphone hiss! I want this without the need to create a dummy
stream.

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