F E H !!!
Replying to the article which bears this article's head.
1) Direct drive turntables do NOT have more low frequency noise than
belt drive turntables. What they DO have is "cogging" distortion, so
named for the stepping motor's tendency to provide an impulse every
t sub s seconds. This impulse does two things:
a) It propigates through the entire platter system, causing noise
pickup at a frequency which is NOT low, and
b) It causes a very slight FM modulation of the material being
reproduced. This effect "seems" to be the cause of most dislike of
direct drive turntable, in fact, it is responsible for the 'unique' sound
of several of the direct drive breed. There are a few turntables using
quadrature drive that do not have this problem. Strangely enough, they
sound a lot like a belt drive turntable. The IM and sideband properties of
this kind of modulation are mind boggling. Try it yourself.
Non-the-less, I still wonder what is wrong with a servo'ed BELT drive.
It has the advantages of both systems, and few of the problems. Its only
problem is its belt, and that is common to all belt drives (funny thing!).
2) "Class A" amplifiers have been touted in the high end market for a long
time. REgardless of advertising noise, class a is class a. If the output
device doesn't conduct linearly through the whole cycle, it ain't class
a. There have been several important new designs in the biasing of NON
class A amplifiers lately, but these amps are not in the high end market,
they don't need to be. There is NO reason why any amplifier has to be in
the high end market.
3) There are several untruths listed under this head. I will cover a couple.
a). The filter doesn't have to have an instantanious change from
on to off. In most cases, the sampling rates are chosen to be ABOVE! the
Nyquist frequency far enough that the filters are not that difficult to design.
In fact, that is usually the one thing that constrains the sampling rate.
b). D/A conversion, since the advent of the digital audio "threat"
has been pushed quite a ways. The D/A that cost 300 $ ten years ago now
costs $80 and works better. If a 16 bit D/A introduces noise above
-96dB, it isn't a 16 bit D/A, by definition. The A/D and D/A introduce
noise only as they quantize the signal to 16 bits. If they do otherwise,
they should be replaced with a relatively inexpensive unit that WILL work
right. So much for that. The signal coming into the A/D may not have 16 bits
resolution, but it isn't any worse than the same signal that is being used
for disc or tape, so that arugement is handwaving.
c). The idea that digital has a lower signal to noise ratio for lower
energy signals is true. So does everything else. If the Signal to Noise
Ratio (SNR) is better, then the noise will be less troublesome, if the noise
is of the same (white) type. Disc's, tape, and the like have exactly the same
behavior, except that the signal disappears at a higher level, indicating that
the noise is causing MORE damage.
As far as standardazation, I couldn't agree more. There are several
systems (Phillips has suporters in Japan, BTW) where there should be
one. The reasons don't even have to do with competition. I could flame
for hours about that.
On the other hand, quad doesn't have much to do with digital, as far as
public acceptance is concerned. I have listened to quad setups, and I don't
like them very much. A proper stereo system sounds more realistic to me
than a quad recording, even including ambiance. I'm not convinced
that quad is better. I am convinced that a record that doesn't lose high
frequencies when it's played, doesn't automatically introduce 3% distortion,
and is washable if it gets dirty, has much to offer. Especially since
it sounds so much better.
Now-- If we could only raise Stowkowski for a few recording sessions.
J.D.Johnston rabbit!jj BTL/MH