[LAU] USB device gives wrong data?

[Fons Adriaensen]

On Fri, Oct 19, 2007 at 02:44:08PM -0700, william estrada wrote:

>    When I use my laptop's sound device and record without a mic, I get
> a file full of x'7f's.  If I do the same with my cheap-o USB device
> I get a file full of x'81's.  The sound quality from the laptop is
> unacceptable, so that is way I want to use the USB device.

Those values are somewhat confusing - your device doesn't produce
8-bit samples, does it ?

A 'perfect' interface would probably produce zeros on silence.
You may be seeing a small DC offset.

Anyway, silence detection based on one particular sample value can't
be expected to work well, there will always be _some_ noise. Better
calculate the RMS amplitude and set a threshold on that.

-- 
FA

Laboratorio di Acustica ed Elettroacustica
Parma, Italia

Lascia la spina, cogli la rosa.