Path: utzoo!utgpu!news-server.csri.toronto.edu!helios.physics.utoronto.ca!ists!yunexus!xrtll!rsnider From: rsnider@xrtll.uucp (Richard Snider) Newsgroups: comp.dsp Subject: Re: A simple, practical sound board Message-ID: <1990Nov7.172516.1045@xrtll.uucp> Date: 7 Nov 90 17:25:16 GMT References: <15912@netcom.UUCP> <16113@csli.Stanford.EDU> <16002@netcom.UUCP> <16150@csli.Stanford.EDU> Reply-To: rsnider@xrtll.UUCP (Richard Snider) Organization: XRTLL - Almost Public Unix, Toronto, Ontario, Canada Lines: 48 In article <16150@csli.Stanford.EDU> poser@csli.stanford.edu (Bill Poser) writes: >In article <16002@netcom.UUCP> ergo@netcom.UUCP (Isaac Rabinovitch) writes: >>All right, my goal of an hour of sound in a megabyte betrayed my >>ignorance of signal theory. So let's bump up the space requirement by >>an order of magnitude. Are we into the real world yet? > >Well, if you just want to use simple sample and not any kind of coding, >you'll need a bit more. Here's how to do the calculation. Suppose you're >going to use one byte per sample. That gives you passable resolution, >though not what you'd want for research or real hi-fi. It's also the >resolution of all of the cheap digitizers. To get good quality speech >you should sample at a minimum of 12K samples/second. This gives you >room for anti-aliasing filtering at about 5KHz (you need to allow >for the fact that the filter cutoff is not perfectly sharp). So, >you need 12K bytes per second. That is 1.2e4 * 3.6e3 = 4.32e7 >bytes per hour, or 43.2MB per hour. So you need another half an order >of magnitude to get into the ballpark. Well, to furthur draw this out, let me get my 2 cents worth in here. If you really wanted to be minamalist, you can get reasonable speech sounds at about 6Khz to 8Khz. (6 sounds a lot like a telephone, 8 is more like a Cheap AM radio). Assuming you also want "numerically perfect" (ie. no error) reporduction, you can almost get 2 to 1 compression using some form of delta encoding (differences between samples). If you are digitizing pure speech (no background sound or music) you also will find that about 17% of this can be stored as silence. (Again, this is from one of my samples, your mileage may vary). If you care to go to approximate compression, you can likely get as much a 3 or 4 times compression. Anyway, time for some math: Say, sampling rate of 8KHz, 2 to 1 compression, and silence is encoded as a 3 byte command so its contribution to a overall size of the file will be negligable if we assume that silence is no change in the input sample for say 300 samples (.0375 seconds). 8000 samples/sec * 3600 sec = 28.8 x 10^6 samples 2 to 1 compression gives 14.4 x 10^6 compressed samples 17% of the above is roughly (very roughly) 2.4 x 10^6 So your total number of bytes is 12 x10^6 Is that any closer ??? Richard Snider ------------------------------------------------------------------------ Where: ..uunet!mnetor!yunexus!xrtll!rsnider Also: rsnider@xrtll.UUCP An unbreakable tool is useful for breaking other tools.