From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from int-mx1.corp.redhat.com (int-mx1.corp.redhat.com [172.16.44.254]) by listman.redhat.com (Postfix) with ESMTP id 1ED563EA53 for ; Tue, 20 Nov 2001 13:36:51 -0500 (EST) Received: from mail.redhat.com (mail.redhat.com [199.183.24.239]) by int-mx1.corp.redhat.com (8.11.6/8.11.6) with SMTP id fAKIapp29271 for ; Tue, 20 Nov 2001 13:36:51 -0500 Received: (from mail@localhost) by mail.redhat.com (8.11.0/8.8.7) id fAKIaoa17942 for blinux-list@listman.redhat.com; Tue, 20 Nov 2001 13:36:50 -0500 Received: from xanadu.home (modemcable084.137-200-24.mtl.mc.videotron.ca [24.200.137.84]) by mail.redhat.com (8.11.0/8.8.7) with ESMTP id fAKIanw17930 for ; Tue, 20 Nov 2001 13:36:49 -0500 Received: from localhost (nico@localhost) by xanadu.home (8.11.6/8.11.6) with ESMTP id fAKIanS09829 for ; Tue, 20 Nov 2001 13:36:49 -0500 X-Authentication-Warning: xanadu.home: nico owned process doing -bs Date: Tue, 20 Nov 2001 13:36:49 -0500 (EST) From: Nicolas Pitre X-X-Sender: To: Subject: Re: Technical Question (was Digital Talking Book Standard ) In-Reply-To: <200111201616.fAKGGAa95386@dc.cis.okstate.edu> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Loop: blinux-list@redhat.com Sender: blinux-list-admin@redhat.com Errors-To: blinux-list-admin@redhat.com X-BeenThere: blinux-list@redhat.com X-Mailman-Version: 2.0.1 Precedence: bulk Reply-To: blinux-list@redhat.com List-Help: List-Post: List-Subscribe: , List-Id: Linux for blind general discussion List-Unsubscribe: , List-Archive: On Tue, 20 Nov 2001, Martin G. McCormick wrote: > Yes, I am a bit slow, but I am catching on. I definitely > need to understand more about time scale shifting methods and how > to accomplish them without adding distortion. > > Each digit represents a moment in time and we can make > things appear to speed up or slow down by intelligently inserting > or deleting information. Exactly. > If we do it on a sample by sample basis, we can make the > recording appear to speed up or slow down with the expected pitch > changes. If we do it on a wave form by wave form basis, we can > appear to keep the same pitch, but speed up the tempo or, for > that matter, we can add extra wave forms and stretch out the > syllables or whatever and slow them down. Right. And therefore you can accurately find out where the waveform boundaries are when dealing with digital sound. The technique consist of finding the best correlation between the original signal with a small moving window of the same signal inside a limitted range. You then get the exact sample position where the current waveform is likely to start and end. Then you only need to duplicate or remove that waveform once in a while with a certain ratio to create the desired effect. > The old pitch correcting devices like the one I presently > use to read magazines butcher the sound because they aren't smart > enough to make sure the next snippet of sound starts at the same > place on the wave form that the previous one ended so we get that > characteristic gravelly sound at high rates. That's because those devices just don't care about signal periods at all, and tend to duplicate or remove an arbitrary fixed duration of signal. Nicolas