Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83 based; site hound.UUCP Path: utzoo!watmath!clyde!burl!mgnetp!ihnp4!houxm!hound!rfg From: rfg@hound.UUCP (R.GRANTGES) Newsgroups: net.audio Subject: Re: Square Wave Response (Now Hold On!) Message-ID: <524@hound.UUCP> Date: Tue, 12-Jun-84 12:35:27 EDT Article-I.D.: hound.524 Posted: Tue Jun 12 12:35:27 1984 Date-Received: Wed, 13-Jun-84 01:10:50 EDT References: <270@whuxj.UUCP> Organization: AT&T Bell Labs, Holmdel NJ Lines: 27 Now hold on just one darned minute, folks. I'm sure I have seen square waves from a CD test record that looked better than anything I've ever seen from a disc (except maybe with the old Weathers' pickup). Mitchell, here you are going on about 20 khz square waves. Almost any amplifier is going to mess that one up today, not to mention the small problem of how do you radiate it acoustically. Webe talking about 1000 hz square waves. The CD medium is inherently capable of producing -off the disc- a "perfect" square wave, where I define perfect as flat topped (in this case response to DC so even a 100 hz or 10 hz square wave would look flattopped) with "vertical" transitions (in this case, a rise time of less than one sample period -24 microseconds). True, some players will show ringing. Most of the photos I have seen show less ringing than what we have become accustomed to with phono cartridges - of which moving coil designs seem to be the worst (?). THe initial article led off with a wild claim, contrary to fact, that everyone seems to have accepted - that CD square wave response is bad. It's not. It's superb! For that matter, so is the impulse response. Somebody donate big bucks to the cause and we'll buy some test discs to take pictures at home. Meanwhile, I'll go by what I've seen printed. A well known rule of thumb is that for a square wave to look good, you need flat response and linear phase between 0.1 and 10 times the repetition rate of the square wave. With rep rates to 1000 hz, the CD medium, even with the poorest "filtering", provides almost perfect response - certainly far better than any other medium in common use. I hate this overkill, why didn't yoiu guys kill this one earlier (Quick, Henry, the Flit!) Dick Grantges hound!rfg