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

On 06/12/2010 12:10 AM, Geoff Beasley wrote:
> Olivier,
> hard to tell from such a small fragment if it's regular or random.
> it maybe irq swapping, or overload compression built into the card or...
> what card is it? describe the signal chain.

I don't know which sound card/chip it is. It's running on a phone, an HTC
Incredible, which has the following specs:
http://www.htc.com/us/products/droid-incredible-verizon#tech-specs

The main chip, which embeds the 1Ghz CPU and a lot of other things, is a
Snapdragon QSD8650:
http://pdadb.net/index.php?m=cpu&id=a8650&c=qualcomm_snapdragon_qsd8650

This is a bit of a do-it-all chip, so I suppose it might embed sound components.
But there's nothing sure about this. Maybe that dmesg could help, but it's a bit
complicated to do this with a remote user.

The signal has being recorded using the internal mic, but the user reported that
the same problem occurs when using a headset with integrated mic.

> try recording at 1/2 level and see if the problem decreases/stops. it's
> more prominent when the violin enters

It's a report from a remote user. I'm already waiting for some more feedback
from him about testing with an external dynamic mic.

Also, about level, Android doesn't give me any access to the hardware mixer. So
the only way to decrease level would be to record from a greater distance.

>From your other mail:
> another thought is resampling if it's a 48k card running @ 44.1 it may be resampling on the fly...

I'm reading audio PCM data through the Android Java API, which is a bit abstract
but doesn't convert the native ALSA samplerate AFAICS.

Right now, I highly suspect that the HW performs some automatic gain control or
so, suitable for phone communications, but altering the signal in this case.

--
  Olivier
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