Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site watdcsu.UUCP Path: utzoo!watmath!watdcsu!herbie From: herbie@watdcsu.UUCP (Herb Chong, Computing Services) Newsgroups: net.audio Subject: Sheffield CDs and why they sound bad Message-ID: <460@watdcsu.UUCP> Date: Mon, 1-Oct-84 20:01:05 EDT Article-I.D.: watdcsu.460 Posted: Mon Oct 1 20:01:05 1984 Date-Received: Wed, 3-Oct-84 07:44:09 EDT Organization: U of Waterloo, Ontario Lines: 30 Some people have been complaining about the sound of Sheffield Lab's CD releases. One of the problems with digital recording as attempted in the manner that Sheffield does is that the digital recorder does not have enough dynamic range. We have people in our physics audio lab designing and building a dynamic range compression device for digital recorders because of that. One theory has it that a digital recorder with at least 120 dB SNR is required to provide adequate dynamic range for live digital recording. If you record to capture the peaks of something like LAB-2 (I've Got the Music in Me by Thelma Houston), the lowest levels will be about 40 dB below that. This leaves you with 50 dB SNR, which is fine for analog systems, though not too listenable, but not for digital systems. This ratios is a voltage difference of only about 300 times. This means that the lowest range is quantized with only about 8 bits (2^8 = 256). What does 8 bit quantization sound like? I've heard demos at 10, 8, and 4 bits quantization. Something sounds wrong at 10 bits; at 8 bits, everything sounds harsh; at 4 bits, the sound is barely recognizable. A compressor can be used to place the signal up where more bits are being used and quantization error is not as noticeable. This is a problem with all digital recording systems handling a high dynamic range signal. More bits are required, or a signal compression system, to get around this. Of course, 120 dB SNR is hard to maintain in analog equipment, and a digital system using linear encoding would require 20 bits to get that much SNR, and finally, the number of bits generated would be 1.5 times as great. Any comments? Herb Chong, BASc Computer Consultant Department of Computing Services University of Waterloo