[LAD] crosstalk between jack clients/ports?

Adrian Knoth adi at drcomp.erfurt.thur.de
Wed May 27 09:04:20 UTC 2015


On 05/27/15 10:35, Gordonjcp wrote:

>> I want to avoid the echo and I have two ideas where the problem can be:
>> 1) there is a crosstalk between jack ports/clients
>> 2) there is a crosstalk in my HW (mainboard sound device with
>> intel_hda driver)
> Most likely the latter.  Check you haven't got the mix parameter
> turned up.

What Gordon said. There is absolutely zero crosstalk in digital systems,
it's a concept from analogue.

In a digital system, each port/channel is a memory buffer. Nothing
accidentally touches this buffer, and if so, the signal would be totally
ruined (think of random bit flips in digital samples).

For an attenuated and delayed signal, you'd need to multiply and add the
initial signal, e.g., out=0.4*remote[-X]+local. This doesn't happen by
accident, something is actively feeding the output back into the stream.

I agree with Gordon's assessment that PC2 is most likely recording from
Mix ("record everything that goes to the hardware outs"), thus creating
a delayed loop.

The fix is to open alsamixer -c X and choose "Mic in" in the records tab
instead of "Mix".



HTH


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