Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site drune.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!mtuxo!drutx!drune!mohler From: mohler@drune.UUCP (MohlerDS) Newsgroups: net.audio Subject: Re: cd players? (answers) Message-ID: <19@drune.UUCP> Date: Fri, 16-Aug-85 22:35:03 EDT Article-I.D.: drune.19 Posted: Fri Aug 16 22:35:03 1985 Date-Received: Tue, 20-Aug-85 04:39:55 EDT References: <226@geowhiz.UUCP>, <4159@alice.UUCP> Organization: AT&T Information Systems Laboratories, Denver Lines: 88 Andy, In your note you fail to mention the key differences and reasons for digital filter - oversampling vs. analog filter - non oversampling! I am replying to add some facts to that question and ask for the netters to talk more productively on the net about CD players - you know, discussion where we all learn rather than some of us wanting to have the last word - wouldn't that be nice! The digital filter - oversampling approach allows you to spread the quantization noise over 4x the bandwidth yielding 1/4 the effective noise! It also allows you to use a cheaper or better quality 14 bit DAC instead of a more expensive or lower quality 16 bit DAC for approximately the same performance! A digital filter won't cause all kinds of ringing like an analog filter will! This is a key issue since a lower cost system has much more potential for preamp distortion due to slew-rate or speed related distortions than a high priced system, making it even more important that a low budget buyer of a CD player pick a digital - oversampled CD player! For those that aren't familiar with speed induced distortions: the higher the input level and frequency the better the preamp will have to be to avoid distorting the signal. Also an active filter is more difficult to manufacture than a digital filter! The frequency response of an digital - oversampled unit will be flatter than an analog - non-oversampled unit and it won't vary (as much) with time, temperature, humidity etc. So, you can get a better manufactured or cheaper digital - oversampled CD player with lower noise, less risk of slew-induced distortions - no ringing, and flatter frequency response (other than with a one clock - beat frequency avoidance scheme) or pick the analog - non-oversampled approach! The variation in response is audible and measurable on an analog - non-oversampled unit as is lack of filter alignment, slew rate distortions, noise level providing you know how to measure and listen for (using test disc's) these problems. If you don't believe this, borrow a scope and a test disc and look and listen since if you disagree you have either: A) haven't measured players B) listened and used music instead of test tones C) don't care D) other - I don't accept that you disagree since it has been proven! By myself and by Audio experts in labs that tried such tests and yes the levels were matched and the results were statistically significant. Also, lets say you don't care, if it is this hard to hear and measure the differences, you still get either a better built or cheaper unit with a digital - oversampled system!! For the record: 1) Some of this is an oversimplification for those that simply want to buy a unit without making a career out of it. 2) I have spent the last 3 years working on digital signal processing and digital circuit design and have measurements to documant what I say is true as does N. V. Philips! 3) I think that rather than people wasting time with this argument of what amounts to opinion, it would be far more productive to talk about facts! It would be far more informative and interesting to discuss open unsolved issues like: Has anyone started looking at rise time limitations in a CD player due to the 44KHZ sampling rate vs. the psychoacoustic fact that the rising edge of a wave-form (ictus) has a definite bearing on audible cues that make a recording sound more or less like live? Or has anyone started looking at the fact that the only way to realize the potential of the CD player is to never use a low speed tape medium in recording due to frequency modulation distortion, modulation noise and massive phase shifts induced in such units? Or has anyone looked into how much the CD players tendency to distort lower levels more than high levels degrades the sound potential of a CD player (if any?). I SUBMIT THAT THIS WOULD BE MORE PRODUCTIVE THAN BEATING THE XXIV OUT OF THE SAME OLD DISAGREEMENTS!! 4) I DO NOT MEAN TO DUMP ON ANDREW, I SUGGEST THAT MANY OF THE CD PLAYER POSTINGS HAVE BEEN INACCURATE, OPINIONATED, OR UNINFORMED AND WE COULD BE LEARNING SOMETHING RATHER THAN WASTING TIME. I MERELY CHOSE ANDY's ARTICLE TO POINT OUT ONE OF MANY INACCURACIES AND MAKE A PLEA FOR BETTER MORE EFFECTIVE DISCOURSE. David S. Mohler AT&T - ISL @ Denver drune!mohler or druxu!mohler