Re: [linux-audio-dev] Latency and feedback problems: soundcard with live microphone pass-thru, optimal solution ?

From: Jens M Andreasen <jens.andreasen@email-addr-hidden>
Date: Sat Oct 29 2005 - 18:16:53 EEST

Benno!

There are some missing parameters in your description, but I will
assumme your problem arises out of the monitor-mix rather than the
house-mix.

Suggestion: Invert the phase of the offending microphone. This should
kill dead feadback in the frequency-band currently annoying you. The
downside is that it will also emphasize other frequency-bands that did
not pose a problem before. The theory is that those resonanses will be
minor relative to your current major problem.

mvh // Jens M Andreasen

On Fri, 2005-10-28 at 13:26 +0200, Benno Senoner wrote:

> Hi all,
> I would like to route a microphone through a sound card and back to
> powerful amplified speakers.
>
> As we know in analog PA gear you have the microphone feedback problem
> (usually it comes in form
> of high pitched whistle sounds).
>
> But if I route a mic from into the soundcard and out to the speakers,
> there will be a small delay
> due to the audio card buffers. Even if it's only a few msecs it makes
> the problem much worse
> than in the case of analogue gear because the feedback sound will come
> in chunks that's one audio card buffer at time.
> For example if I use 64 samples per buffer which gives me acceptable
> latency for a live singer, the feedback noise
> could possibly generate a much lower pitched signal/interference (I
> assume something like 44100/64 Hz) which is I think
> not easy to filter out compared to the high pitched feedback (is in the
> latter case sufficient to cut some high frequencies using an EQ ?).
>
> How can one solve the feedback problem in case of mic to speaker delays
> of let's say 5-10msecs ?
> Is an echo canceller algorithm needed ? If yes does this compromise the
> quality of the input signal (the singer).
>
> I think this is a very interesting topic and it would be cool if
> knowledgable people could come up with topics and ideas.
> (for example people that are good at DSP, room correction etc, like Fons
> A. etc).
>
>
> PS: I know that cards like DELTA 1010 and others (RME) can do zero
> latency monitoring (hardware pass-thru) but
> I'd prefer a software based routing since you can apply effects and
> stuff before forwarding the output.
>
> thanks for infos and toughts
> Benno
>
> http://www.linuxsampler.org
>

-- 
Received on Sat Oct 29 20:15:07 2005

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