Re: [LAD] Looking for the cause of pulsating noises

On 06/11/2010 02:10 PM, Ralf Mardorf wrote:
> Olivier Guilyardi wrote:
>> Here is the sample, it's a musical flute and violin recording:
>> http://sound.samalyse.org/tapemachine/pulsations.wav
>>
>> Listen carefully and you will here small pulsations.
>
> Here I didn't need to listen carefully, it's unmistakable. I know this
> kind of noise when doing recordings with anlog consumer cassette
> recorders and cheap microphones and cables.

Yes, you're right, the noises are obvious.

> Listen carefully and you will here this or similar pulsations for the
> sine wave too, perhaps just some background noise, when the sine was
> recorded.

I think these are background noises. It has been recorded by putting the phone
near the computer speaker. I'd swear that this is murmuring in the background.

> What happens for recordings without microphones?

There is no line-in, only a TRRS jack for both input and output. So I don't see
how to record without a mic. The user has tried to plug a headset with an
integrated microphone, and he said that the noises were still here.

He also reported the following: "if I rig up a TRRS 3.5 mm jack to XLR adapter
and use a "real" microphone the recording seems to be clean (though with other
issues, perhaps ground loops or impedance mismatch or something)".

I've seen similar problems when plugging an external microphone. That produced a
huge constant noise. I doubt that the user can really determines if the
pulsations are gone in this situation.

On the software side, couldn't a sample rate conversion produce that kind of
pulsations? I'm not doing any, but I haven't checked Android sources about this.

--
  Olivier
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