[pulseaudio-discuss] Can module-echo-cancel reduce the background noise?

[Maarten Bosmans]

2011/9/15 Lin, Mengdong <mengdong.lin at intel.com>:
>
>> > (1)     Reduce the echo of myself during audio recording in a room
>>
>> I'm not sure about what you mean here precisely. But in general this
>> isn't called echo, but feedback. The only difference between the two
>> is that with echo you have a large (~ > 20ms) delay and you can here
>> two distinct versions of the sound. With feedback the delay is in the
>> order of a typical wavelength (~ < 5ms) and you can hear a (often
>> high-pitched) ringing sound.
>>
>> The obvious solution would be not playing back the recorded audio over
>> the speakers. Is there any particular reason you want to hear
>> yourself?
>
>> And if the recording is for musical purposes, I'd strongly advise to
>> get a decent microphone. I mean, when a band is performing on stage
>> they can hear themselves over the monitor quite loud, but there's no
>> feedback and no echo-cancelling is used. (wel actually there are
>> devices called feedback-killers, but those are more automatic
>> equalizers and are generally not used for music event, but rather for
>> speech)
>>
>
>
> Thanks a lot for the information! I have two use cases in my mind:
> (a) If I speak in a large empty room and use a microphone to record my voice (no playing back), can PA module-echo-cancel reduce the echo/feedback?

There's no feedback here, because you're not playing back anything,
just recording. Most likely there is no echo either, just some
reverberation from the room (although the distinction between echo and
reverb is not that clear). Eliminating unwanted room acoustics is not
simething module-echo-cancel was designed for and I doubt it would
work.

>   You mentioned to use a decent microphone, is such a microphone can reduce the feedback via its hardware?

Yes, indeed, but probably not in the way you expect it, there's no
processing going on. In general for these applications you want a
directional microphone, and not a omnidirectional one. If you position
sound source (you), microphone and speaker correctly, almost no audio
from the speaker will bleed into the microphone, thus no feedback.

> (b) When I do a presentation in a hall (both recording and playing back, and maybe multiple speakers), can PA module-echo-cancel reduce the echo/feedback?

Do you currently have issues with the echo when recording such live
events? Really, these recordings should be free of echo if you set
thing up properly. Again, having the right equipment and installing it
correctly is key here.

Maarten