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From: "ROSSI J.A." <rossi@nusc.ARPA>
Date: 20 May 86 14:17:00 PST
Subject: CDs VS LPs
Reply-To: "ROSSI J.A." <rossi@nusc.ARPA>
For some time now I have been considering adding a CD player to my somewhat ancient audio equipment. For the most part, the thing that had turned me off was the high cost of the music after purchasing of the relatively inexpensive disks. At $15-18 the CDs certainly are not cheap. Well, lately I decided that maybe I was ready to make the step. What with the event of $179 CD players,I figured I could afford one. Just as I was about to purchase one, this quarter's issue of the Computer Music Journal arrived at the lab. There was an interesting critical/review article on CD players as well as digital mastering and digital reproduction of music as a whole. Finally, I found a non-profit, musically (as opposed to engineering/technology) oriented, no-holds barred review of the state of the art in music reproduction (Done at MIT, no less). The results, wghich I will summarize briefly here, were surprising, especially considering all the 'hype' the CD medium has been receiving lately. Greenspun, P. and Stromeyer, C.F. Audio Analysis IV : Compact Disk Players, 'Computer Music Journal', 1986, '10(1)', pp 87-95. The article is somewhat technical so I'll summarize, quoting directly, where appropriate. Point number 1. Using technology available today, CD players can not achieve the high fidelity possible with conventional turntables using moving magnet, or moving coil cartriges. ... When testing the fidelity of CDs vs an audiophile stereo system the authors found that for high quality analog media , (i.e., high quality pressings), the analog equipment produced remarkably beter fidelity. Consider, the frequency response of a typical home use cartrige such as Audio Technica, Grado, Sure etc with frequency response in excess of 35K Hz, going to an amplifier (again the type you might have at home in a standard system >$500 receiver or integrated amp) which is linear out to about 40K, reproducing music with harmonic content out to 48K, in comparison to the CD response which is electronically limited to 20K, going through the same amp and speakers. It stands to reason that if nothing else, the analog system was going to produce the best frequency fidelity. Of course, this argument must be tempered with the knowledge that true audiophile recording pressings in standardmedia are hard to come by, however, techniques such as DBX encoding, have been used to enhance the performance of vinyl (out to 90 dB dynamic range, giving vinyl similar dynamic characteristics to CDs, upcutting their only real sonic advantage. Point number 2. CDs are getting better at sound reproduction but the best CDs will be cut from analog mastered tapes (i.e., the worst of all possible combinations is digitally mastered tape to CD). The problem in the CDs play- back comes mainly from phase distortion, it has been corrected by changing the sampling rate from 44.1 Khz (the initial Sony standard) up to 176.4 KHz and incorporating better analog and digital filtering networks. With the newer technology, phase distortion has been eliminated for frequencies up to just under 21K (notice however, there is no comparable phase distortion in cartrige systems which extend frequency response up to 40KHz). Therefore, CDs are now capable of faithfully reproducing (more or less) musical frequencies up to 20K more or less perfectly (or at least as good as the best analog equipment). "There is experimental evidence that frequencies beyond 20K are important for the preception of transient sounds, although surprising little research has been conducted in this area. It is well established that that most humans can not perceive steady state tones much above 20KHz, but it is also well est- ablished that the ear is highly nonlinear. The most detailed-sounding records come from companies that use high band with tape recorders (analog) and mastering equipment. If 'ultrasonic' frequency response is important, CDs may never sound as detailed as records (p 93)". The authors site the failure of digital recording techniques to correctly record musical signals as being mainly a problem with aliasing (sampling rate insufficient to make proper time/amplitude discriminations in a complex signal), phase distortion (when the propragation time through a circuit is different for different frequencies),and ringing (when using a steep anti-aliasing filter, a multiplying of frequencies due to extremely phase-incoherent characteristics). Most of these problems stem from the use of extremely steep sloped filters ... "The design therefore calls for 90dB of attenuation within thw one-tenth octave that lies between 20KHz and 22.05 KHz, which requires a 900 dB/octave filter. As one of us noted earlier in this series (Greenspun, 1984), it is very difficult to design a filter this steep that doesn't introduce severe nonlinear dis- tortion and ringing aftertransients (p. 87). Thhe conclusion is that, although they did use 'primo' analog components (they also used CD players averaging over $1000 in price, however), except for dynamic range diferences (which are easily fixed by companding circuits such as DBX), more faithfull recording/reproducinmg is possiblle with analog equipment. The authors final comments (now all you anti-corporate, haters of the music industry's scrotum grabbing techniques, who own CDs, take note). "It is possible that the construction of an oversampling tape recorder that introduces no phase distortion or aliases will alleviate many of the medium's problems, but it is also possible that imperfect digital-to-analog converters, quantization noise, and other distortions will prevent the CD from becoming a truely high fidelity medium (p 93)." "Aiwa's president, Heitaro Nakajima, and one of the original proponents of the CD while a vice-president of Sony, put it best in a letter explaining why such a low sampling rate was chosen for the CD (caps mine) 'We had to decide on the cutoff point for the sampling frequency, and we HAD TO TAKE ECONOMIC AND PRODUCTIOV FACTORS INTO CONSIDERATION. The CD system WAS NOT DESIGNED as the ultimate level sound reproduction medium. However, THIS DOES NOT MEAN WE FEEL ANY NEED TO CHANGE THE PRESENT STANDARD.' (p 94)". So what does all this mean? First, we probably don't want a CD version of The Dreaming anyway, since it is a highly 'transient' piece of music and would only be belittles bu a CD reproduction. Maybe we should push for a DBX encoded version. Second, it means that I personally am going to stay with high quality pressings and dynamic enhancement insteas of getting sucked into the recording/record industry's latest sham. By the way, I understand that since CD's were chewed up so well, the next corporate gambit is going to be a return to quadrophonics, except this time, done right (no doubt in this case 'done right' means that propoganda will be immense, Len Feldman and the boys will eat it up, and that the corporate dollar will be better spent duping the public into another, software intensive expense which will enable the empire to continue to have fuel as the CD myth is finally disclosed. 'Read em' and weep' John ------