Return-Path: <owner-rsgb_lf_group@blacksheep.org> Received: (qmail 27711 invoked from network); 10 Dec 2003 16:22:38 -0000 Received: from unknown (HELO netmail00.services.quay.plus.net) (212.159.14.218) by ptb-mailstore with SMTP; 10 Dec 2003 16:22:38 -0000 Received: (qmail 28491 invoked from network); 10 Dec 2003 16:22:36 -0000 X-Filtered-by: Plusnet (hmail v1.01) X-Spam-detection-level: 11 Received: from post.thorcom.com (193.82.116.20) by netmail00.services.quay.plus.net with SMTP; 10 Dec 2003 16:22:29 -0000 X-Fake-Domain: majordom Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1AU75q-0007ZP-GA for rs_out@blacksheep.org; Wed, 10 Dec 2003 16:21:42 +0000 Received: from [165.254.4.18] (helo=mail.mcf.com) by post.thorcom.com with esmtp (Exim 4.14) id 1AU75p-0007ZG-7k for rsgb_lf_group@blacksheep.org; Wed, 10 Dec 2003 16:21:41 +0000 X-Fake-Domain: vaiosn Received: from vaiosn (66.65.127.140) by mail.mcf.com with ESMTP (Eudora Internet Mail Server 3.2.2) for <rsgb_lf_group@blacksheep.org>; Wed, 10 Dec 2003 11:21:42 -0500 X-Bad-Message-ID: no DNS (vaiosn) Message-ID: <001501c3bf39$aedd0fb0$0401a8c0@vaiosn> From: "Stewart Nelson" <sn@scgroup.com> To: rsgb_lf_group@blacksheep.org References: <01C3BF2E.2774C230.g4jnt@thersgb.net> Date: Wed, 10 Dec 2003 08:21:34 -0800 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2720.3000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Subject: Re: LF: Related Technical Query - Soundcard calibrator Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Checker-Version: SpamAssassin 2.60 (1.212-2003-09-23-exp) on post.thorcom.com X-Spam-Status: No, hits=0.0 required=5.0 tests=none autolearn=no version=2.60 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@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-Spam-Rating: 2 Hi Andy, IMO, you are being too much of a perfectionist to worry about sin(x)/x. I believe that x must be pi * fsig / fsample, because the spectrum goes to zero at multiples of fsample. So at 20 kHz the spectral density is 20*log(sin(pi*20/5000)/(pi*20/5000)). This is about 0.00023 dB down from the level near DC. The remaining question is what's the scale factor. I believe that you can ignore the high frequency behavior, and pretend that the power is spread over half the sample frequency. If your shift register puts out +/- 1V square wave into 1 ohm (total RMS is one watt), then the low frequency power density is 10*log(1/2.5E6) = -64 dBW/Hz. My math is really weak, so I verified this by simulating a random square wave, and looking at the spectrum with Cool Edit. 73, Stewart KK7KA ----- Original Message ----- From: "Andy talbot" <g4jnt@thersgb.net> To: <rsgb_lf_group@blacksheep.org> Sent: Wednesday, December 10, 2003 6:59 AM Subject: RE: LF: Related Technical Query - Soundcard calibrator > Yes, the power spectrum of a SIN(X) / X pattern. > > To Brian 'GVB, the limits will be (theoretically at least) - infinity to > infinity, but in practice a few lobes will be sufficient, say about +/- 5 > > Andy