Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!uwm.edu!csd4.csd.uwm.edu!info-high-audio-request From: cjc@ulysses.att.com (Chris Calabrese) Newsgroups: rec.audio.high-end Subject: Re: data compression (was: What's up with RDAT?) Message-ID: <11988@uwm.edu> Date: 9 May 91 12:53:57 GMT Sender: news@uwm.edu Lines: 46 Approved: tjk@csd4.csd.uwm.edu Originator: tjk@csd4.csd.uwm.edu 09nilles%cuavax.dnet@netcon.cua.edu (Fiver Toadflax) writes: >> From: "William K. McFadden" >> >> This isn't as irrational as you might think. The problem with the DCC >> compression scheme is that signal degradation occurs with each >> encoding. > >I haven't seen the details(algorithm) of the DCC compression scheme, but >if it is any decient, nothing will be lost. Afterall, look at programs >such as PCZIP, UUencode, compress. ALL of those programs take programs, >ASCII text files, etc and shrink them. Some better then others. But >no data is lost unless the file gets corrupted. And there is no difference >between a CD with music recorded on it then the CD ROMS used by computers. >I mean that both are simply a long string of 1's and 0's. So a well written >compression routine should not have, on the average any data loss. > > Dave PCzip (pkzip, etc too), compress, pack, and other such data compression schemes talked about above are designed to be lossless. The rely on being able to re-encode the data in a more efficient manner. The DCC compression, on the other hand, is not designed to be lossless. In fact, the whole point of it is to _throw_out_part_of_the_signal. The theory is that the brain just can't comprehend all that's going on and you'll hear _exactly_ the same thing, even when a good chunk of the signal is nuked. It works pretty well too. Tests on similar schemes here at Bell Labs (I didn't take place in them, so this is second hand) showed that people couldn't tell the difference (no statistically significant results). I don't know if you can do lossless digital-to-digital copying, however. That depends on how you implement it, not on the underlying compression scheme. BTW, uuencode is doesn't do any compression. In fact, files are bigger afterward. Name: Christopher J. Calabrese Brain loaned to: AT&T Bell Laboratories, Murray Hill, NJ att!ulysses!cjc cjc@ulysses.att.com Obligatory Quote: ``pher - gr. vb. to schlep. phospher - to schlep light.philosopher - to schlep thoughts.''