Return-Path: Received: from mtain-md03.r1000.mx.aol.com (mtain-md03.r1000.mx.aol.com [172.29.96.87]) by air-mc03.mail.aol.com (v129.4) with ESMTP id MAILINMC034-a8de4bf685e935e; Fri, 21 May 2010 09:08:57 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-md03.r1000.mx.aol.com (Internet Inbound) with ESMTP id 341D3380000E2; Fri, 21 May 2010 09:08:56 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1OFRwW-0001uz-5s for rs_out_1@blacksheep.org; Fri, 21 May 2010 14:07:12 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1OFRwV-0001uq-Qg for rsgb_lf_group@blacksheep.org; Fri, 21 May 2010 14:07:11 +0100 Received: from mout0.freenet.de ([195.4.92.90]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1OFRwU-00074I-PE for rsgb_lf_group@blacksheep.org; Fri, 21 May 2010 14:07:11 +0100 Received: from [195.4.92.15] (helo=5.mx.freenet.de) by mout0.freenet.de with esmtpa (ID dl4yhf@freenet.de) (port 25) (Exim 4.72 #3) id 1OFRwT-0002ak-K2 for rsgb_lf_group@blacksheep.org; Fri, 21 May 2010 15:07:09 +0200 Received: from blfd-4db1b5ef.pool.mediaways.net ([77.177.181.239]:1705 helo=[192.168.0.21]) by 5.mx.freenet.de with esmtpa (ID dl4yhf@freenet.de) (port 25) (Exim 4.72 #3) id 1OFRwT-00085h-5u for rsgb_lf_group@blacksheep.org; Fri, 21 May 2010 15:07:09 +0200 Message-ID: <4BF6857A.1000707@freenet.de> Date: Fri, 21 May 2010 15:07:06 +0200 From: =?ISO-8859-1?Q?Wolfgang_B=FCscher?= User-Agent: Thunderbird 2.0.0.24 (Windows/20100228) MIME-Version: 1.0 To: rsgb_lf_group@blacksheep.org References: <008f01caf784$779a11d0$0301a8c0@your91hoehfy9g> <4BF4FBF4.2020208@iup.uni-heidelberg.de> <4BF53399.4010403@iup.uni-heidelberg.de> <4BF5387F.2040906@legal-medicine.de> <4BF53D71.8050404@iup.uni-heidelberg.de> <4BF5420D.5020604@legal-medicine.de> <4BF54BE5.4090907@iup.uni-heidelberg.de> <4BF56400.5010904@legal-medicine.de> In-Reply-To: <4BF56400.5010904@legal-medicine.de> X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,none Subject: Re: VLF: Clipping or blanking?? Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=none autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false x-aol-global-disposition: G x-aol-sid: 3039ac1d60574bf685e82495 X-AOL-IP: 193.82.116.20 X-Mailer: Unknown (No Version) Hi Peter, Stefan and the group, Peter asked: > How to lock the sample rate of a sound card against a MSK modulated signal? > The only idea I have is to demodulate it and locking a re-sampling process > against one of the two carriers - by software. May be there's the key. > Usually no resampling - that would be too much overhead. The soundcard's ever-changing sample rate is simply taken into account at various processing stages, most noteably the NCO (numerically controlled oscillator) which mixes the observed band down to baseband (before the decimator chain, and before the complex FFT). The MSK signal, when used as reference, is indeed demodulated (but not decoded of course) by squaring it after lowpass-filtering and decimation. The two peaks at f_center +/- 0.75 * bitrate are used to measure the instantaneous sampling rate (using a complex FFT, and comparing the phases in the peak FFTs beens between two calculations, i.e. once every few seconds). The program then tries to predict the sampling rate for the next chunks of digitized samples for the rest of the application, because the length of a processing chunk is usually much less than the measuring interval. Very fast sample rate drift cannot be compensated this way, but for FFT resolutions in the range of a mHz or less, it's sufficient. Cheers, Wolf .