From mboxrd@z Thu Jan 1 00:00:00 1970 From: Manuel Jander Subject: RE: Sound with metal effect Date: Fri, 01 Apr 2005 12:58:37 -0400 Message-ID: <1112374717.3167.21.camel@localhost> References: Reply-To: mjander@users.sourceforge.net Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: alsa-devel-admin@lists.sourceforge.net Errors-To: alsa-devel-admin@lists.sourceforge.net List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , List-Archive: To: alsa-devel List-Id: alsa-devel@alsa-project.org Hi, On Fri, 2005-04-01 at 09:39 +0200, Giuliano Pochini wrote: > On 31-Mar-2005 Laurielle LEA wrote: > > > I'm integrating ALSA to my voipclient (softphone) and > > my problem is the sound received by the remote user is > > with metal effect. > > VoIP uses 8KHz sampling rate IIRC. What did you expect ? Metal effect indicates bad antialiasing filters. That may be caused by bad hardware, bad hardware setup or a very bad software emulation. 8KHz sound obviously does not sound CD-quality, but it should not have aliasing noise. It should just sound with lower bandwidth, specially higher frequencies being cutoff. Standard phone bandwidth is between 300-3400 Hz. Software resampling through removing or adding samples, and doing some mean value cooking is far from optimal. It would be better to use a recursive Z-tranform (or whatever math tool you prefer) synthesised algorithm. Even a small IIR filter for postprocessing would barely consume any CPU power. Such algorithms are well known and available. Best Regards -- Manuel Jander Dipl.-Ing. Fachrichtung Elektronik ------------------------------------------------------- This SF.net email is sponsored by Demarc: A global provider of Threat Management Solutions. Download our HomeAdmin security software for free today! http://www.demarc.com/Info/Sentarus/hamr30