Return-Path: Received: (qmail 22274 invoked from network); 23 Jan 2001 15:48:22 -0000 Received: from unknown (HELO murphys-inbound.servers.plus.net) (212.159.14.225) by excalibur.plus.net with SMTP; 23 Jan 2001 15:48:22 -0000 Received: (qmail 19359 invoked from network); 23 Jan 2001 15:42:33 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by murphys with SMTP; 23 Jan 2001 15:42:33 -0000 Received: from majordom by post.thorcom.com with local (Exim 3.16 #1) id 14L5U2-000136-00 for rsgb_lf_group-outgoing@blacksheep.org; Tue, 23 Jan 2001 15:35:46 +0000 X-Priority: 3 X-MSMail-Priority: Normal Received: from mail.sci.fi ([195.197.53.226] helo=vasta.saunalahti.fi) by post.thorcom.com with esmtp (Exim 3.16 #1) id 14L5Tx-000131-00 for rsgb_lf_group@blacksheep.org; Tue, 23 Jan 2001 15:35:42 +0000 Received: from pmk2 (CDXCIII.hdyn.saunalahti.fi [195.74.4.193]) by vasta.saunalahti.fi (8.10.1/8.10.1) with SMTP id f0NFZrg02143 for ; Tue, 23 Jan 2001 17:35:54 +0200 (EET) X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 From: "Paul Keinanen" To: rsgb_lf_group@blacksheep.org Subject: LF: Re: Accuracy of Soundcards, programs, an d related stuff Date: Tue, 23 Jan 2001 17:35:52 +0200 Message-ID: References: <65AECDF1F89AD411900400508BFC869F0D7549@pdw-mail-1.dera.gov.uk> In-reply-to: <65AECDF1F89AD411900400508BFC869F0D7549@pdw-mail-1.dera.gov.uk> X-Mailer: Forte Agent 1.7/32.534 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: On Tue, 23 Jan 2001 09:33:52 -0000, Talbot Andrew wrote: >Is it a coincidence I wonder, that the 'standard' Soundcard / CD >sampling rate is a multiple of the squares of the small prime numbers. >ie: > > 44100 = 2 * 2 * 3 * 3 * 5 * 5 * 7 * 7 > >Spooky ! >Certainly simplifies decimation to a wide variey of lower rates. For >a CW tone centred on 800Hz, 11025 / 5 = 2205Hz would be ideal, letting a >CW filter of up to 400Hz bandwidth handle removal of the aliasing >products above 1102Hz. or 44100 / 5 = 8820 for a more accurate value >for voice bandwidth signals. The original reason for the sampling rate in the 44 kHz region is that video tape recorders were used widely in early digital audio experiments long before the CD. There was usually three samples/channel in every video line between the synch pulses. With 525 lines @ 60 Hz interlaced, that would give 47250 samples/channel. However, there is a large number of lines used for vertical synch, thus, the samples had to be averaged over a single field, giving rates such as 44056 Hz or 44100 Hz. In order to be able to store digital audio on both 525@60 Hz and 625@50 Hz video recorders, the sampling rate have to contain the 2, 2, 3, 5 and 5 primes. Thus, each video field would contain 735 resp. 882 samples and with 3 samples/line, 245 resp. 294 active lines/field or 490 resp. 588 lines/frame are used, the rest was taking by the vertical blanking. Paul OH3LWR