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

[Jens M Andreasen]

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
> 
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