Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!cs.utexas.edu!uunet!mcsun!ukc!cam-cl!news From: nbvs@cl.cam.ac.uk (Nicko van Someren) Newsgroups: comp.compression Subject: Re: Compression of 16-bit sound files. Message-ID: <1991Apr22.100239.1788@cl.cam.ac.uk> Date: 22 Apr 91 10:02:39 GMT References: <1991Apr21.002203.4414@nntp-server.caltech.edu> <1991Apr21.163913.2249@smsc.sony.com> <1991Apr21.185611.8680@nntp-server.caltech.edu> Reply-To: nbvs@cl.cam.ac.uk (Nicko van Someren) Organization: U of Cambridge Comp Lab, UK Lines: 32 As I see it there are three reasons why the CD standard people (Philips?Sony) did not put in compression: 1) They would need extra hardware to decode it and the cost was high enough already. 2) The data rate would end up uneven because some bits would compress better than others. Do you remember how much RAM cost in 1983? 3) Using compression would make it harder to gloss over the errors that the correction hardware could not fix. If you lose raw data it is probably easier to guess what it was. The whole idea of 'lossless' or 'lossy' compression of signals that are to be put into your ear seems a bit silly to me anyway. The fact is it has alot to do with the person in question. If you look at the data that gets stored most of it is only about 13bit as most music spends its time at least 10dB down from the peal level. 16bit linear is too high a resolution at high amplitudes and too low a resolution at low ones. A 12 or 13 bit log system would give better quality for the dynamic ranges that music has and take up only 3/4 of the space (or give you 1/3 more time). While log ADCs cost more you only have to make a very few of them and log DACs are pretty simple. So to go back to the original topic of the thread, if you want to compress your sound files, try storing 10bit log values. It gives you 1.6:1 compression and I doubt you will notice the 'loss'. Nicko +-----------------------------------------------------------------------------+ | Nicko van Someren, nbvs@cl.cam.ac.uk, (44) 223 358707 or (44) 860 498903 | +-----------------------------------------------------------------------------+