From mboxrd@z Thu Jan 1 00:00:00 1970 From: Fredrik Lingvall Subject: Aliasing on ALi5451 Date: Sat, 24 May 2003 10:18:17 +0200 Sender: alsa-devel-admin@lists.sourceforge.net Message-ID: <3ECF2AC9.8070503@signal.uu.se> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Return-path: Errors-To: alsa-devel-admin@lists.sourceforge.net List-Help: List-Post: List-Subscribe: , List-Unsubscribe: , List-Archive: To: alsa-devel@lists.sourceforge.net List-Id: alsa-devel@alsa-project.org Hi! I've tried to do loadspeaker identification using the ALi5451 chipset in my laptop. I saw a strong drop in the spectrum above ~2kHz when a ran the ADC:s at 44100 (I used a high quality microphone and a mic pre-amp). I then wired the audio output directly to the input with the same result - strong attenuation above 2kHz (I used wideband white noise as identication signal). Then I generated a chirp signal (5 sec sine sweep from 0-24kHz using Matlab) at 48kHz sampling rate which I recorded using Audacity at 8, 44.1, and 48 kHz. There was clearly freqeuency folding (aliasing) for all sampling freqs except 48 kHz (see the time-freq plot at: http://www.signal.uu.se/Staff/fl/chirp_test.jpg). From the specs of the cs4299 chip (used in ALi 5451) it allways runs at 48 kHz and uses sample rate converters for the other sampling freqs. However, the anti-aliasing filters (if there are any) do not seem to adapt when changing sampling freq. I also checked cat /proc/asound/5451/pcm0p/sub0/hw_params and cat /proc/asound/5451/pcm0c/sub0/hw_params when playing/recording and the sampling freqs. was correct. Is this a driver issue or is it just a bad sound chip? Regards Fredrik ------------------------------------------------------- This SF.net email is sponsored by: ObjectStore. If flattening out C++ or Java code to make your application fit in a relational database is painful, don't do it! Check out ObjectStore. Now part of Progress Software. http://www.objectstore.net/sourceforge