[LAU] USB device gives wrong data?

[william estrada]

Fons,

   Thanks for your reply.

   Yes, the format is U8, it is a simple recording program to make '.wav'
files. The filtering does work when adjusting the 'silence byte'. It
appears that the device drivers are not consistent with this value?
So I will be adding an option to change the value of the 'silence byte'.

   How do I use the RMS value to remove noise?  A URL that I could read?

   Thanks again for your time.

-- 
William Estrada
MrUmunhum at popdial.com
Mt-Umunhum-Wireless.net ( http://Mt-Umunhum-Wireless.net )
Ymessenger: MrUmunhum

> Message: 6 Date: Mon, 22 Oct 2007 08:53:34 +0200 From: Fons Adriaensen
> <fons at kokkinizita.net> Subject: Re: [LAU] USB device gives wrong data? To:
> linux-audio-user at lists.linuxaudio.org Message-ID:
> <20071022065334.GB5840 at linux-2.site> Content-Type: text/plain;
> charset=us-ascii 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.