CDs VS LPs

["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

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