From mboxrd@z Thu Jan 1 00:00:00 1970 From: william estrada Subject: Re: USB device gives wrong data? Date: Mon, 22 Oct 2007 09:58:38 -0700 Message-ID: <471CD6BE.4090209@popdial.com> References: <47192528.9080403@popdial.com> <1193034894.13299.1217094833@webmail.messagingengine.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from MAIL02.inside.adbasesystems.com (mail.1dial.com [64.136.164.73]) by alsa0.perex.cz (Postfix) with ESMTP id 70C722491B for ; Mon, 22 Oct 2007 18:58:34 +0200 (CEST) In-Reply-To: <1193034894.13299.1217094833@webmail.messagingengine.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: alsa-devel-bounces@alsa-project.org Errors-To: alsa-devel-bounces@alsa-project.org To: Clemens Ladisch Cc: "linux-audio-user@lists.linuxaudio.org" , alsa-devel@alsa-project.org List-Id: alsa-devel@alsa-project.org Clemens, I respect your options and appreciate your time, but from what I have read, for a U8 format, silence is represented by a x'7F'. Do you have a source for your option? In pcm_misc.c seems to support your statement: > static struct pcm_format_data pcm_formats[SNDRV_PCM_FORMAT_LAST+1] = { . . > [SNDRV_PCM_FORMAT_U8] = { > .width = 8, .phys = 8, .le = -1, .signd = 0, > .silence = { 0x80 }, So I guess I need to make my filter flexible to match the current hardware device driver? How would you filter out noise? I am new to these interfaces and would like to find a good place to get more information about filters, noise, etc. Any URLs that you could recommend? Thanks again for your time. William Estrada MrUmunhum@popdial.com Mt-Umunhum-Wireless.net ( http://Mt-Umunhum-Wireless.net ) Ymessenger: MrUmunhum Clemens Ladisch wrote: > william estrada wrote: >> I think I have found a problem with the USB sound driver? It appears >> that the current drive returns a x'81' for silence but it should be a >> x'7f'. > > The USB audio driver returns whatever data is sent by the device > >> 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. > > For unsigned 8-bit samples, silence is x'80'. > > Apparently, both devices have some DC offset and are quite noisy. > >> I have written a recording program that I have a 'silence' filter >> that filters out segments of dead air. It works with the laptop's >> sound device but not the USB device. The filter works by remove >> x'7f's after allowing a selectable amount. > > Your filter should be able to detect silence even when noise is present. > >> Sorry for the multiple posting, not sure where is should have gone. > > The the linux-audio-dev list, of course. ;-) > > > Regards, > Clemens >