From: znpt01@trc.amoco.com (Norman P. Tracy)
Newsgroups: rec.audio,rec.video
Subject: Kerry doesn't get it (was: Re: Selecting an LD Player)
Date: 31 Dec 92 15:32:38 GMT
Organization: Amoco Production Company, Tulsa Research
Originator: znpt01@gpss43


I usually avoid flames like this but Kerry Shetline presents a view that is
so diametrically opposed to my experience as a listener to and student of
digital audio that a strong reply is called for.  This is not a personal attack
on KS, we simply have a different paradigm of audio, and I suspect the world.
Excuse the excessive inculsion of previous materal but I need to (re)set the
context of our disagreement.

In article <shetline-301292233743@128.89.19.85>, shetline@bbn.com (Kerry Shetline) writes:
> In article <1992Dec30.073038.14692@uhura.neoucom.edu>,
> wlrc@uhura.neoucom.edu (William R. Cruce) wrote:
> > 
> > In article <1992Dec29.171405.1480@lsican.uucp> michael@Canada.lsil.com writes:
> > >
> > >[...]Error correcting comes to mind here).  If the only "audible" differences
> > >between players comes from the DAC portion (plus power supplies, etc), then with
> > >an outboard DAC, all CD/LD players should sound identical.  Is this a true
> > >statement?
> > 
> > No.  It is not true.  Theta makes a "CD Transport" which is a modified
> > Philips LD player [major mod is to correct for 'jitter'in the digital
> > output, according to their literature].  Fed into their ~$1000 outboard
> > D/A (I forget the model #) it sounds better than a Pioneer CLD-3070
> > LD player fed into same.  Unfortunately the Philips video is no match
> 
> I haven't heard a Theta unit, so I can't tell you whether or not it
> actually sounds better than any other laser disc player.

You would not want to actually LISTEN to the Theta, it might challenge your
cherished belief system (bits-is-bits, perfect sound forever).  Of course
lack of first hand experience never fails to stop a true blue objectiviest
from launching an attack.

> But I do know that
> the *reasons given* for it sounding better were completely bogus
> techno-hype.

For the objectiviest arguments that agree with me are SCIENCE, agruments that
counter me are TECHNO-HYPE.

> The manufacture made claims regarding improved
> error-correction and mechanical stability as reasons for a gigantic leap in
> audio fidelity. The review I read in Video magazine prompted me to write
> this (unpublished) letter:
> 
> -------------------------------------------------------------------------------
> To the editor:
> 
> After reading your review of Theta DigitalUs Theta Data Universal Transport
> (Videotests, Sept. U92), I  must say that not only am I disappointed that
> you were taken in by baseless high-end hype, but that you are helping to
> uncritically promote it. Even the cheapest CD disc transport will usually
> deliver error-free transfer of data, and certainly none but a damaged unit
> reaches the error rates that would effect continuous sound quality (as
> opposed to occasional and quite noticeable pops, clicks, or skips).

So far so good, sort of.  Kerry addresses the first aspect of accurate digital
reproduction, error free data.  This aspect has been worked on hard from day
one of the digital audio revolution and is not a problem from properly
functioning equipment at all price levels.  But he ignores the second critical
aspect of accurate digital reconstruction of an analog signal, timing.

> Data read from a laser pick-up is digitally buffered and clocked out at a
> precise, quartz-crystal timed rate from the buffer.

This is a common misconception dating back to the "gee-whiz, ain't it great"
articles describing CD technology circa. 1983.

> There is no way for
> mechanical jitter to affect sound quality in the way described in your
> review Q no way for all of this talk of massive high-torque motors and
> positive disc clamping to make a bit of difference.
>--------------------------------------------------------------------------------
>
> -Kerry

NOT. Try this. Open any CD/LD player or transport. Now point to the rows of
SIP-RAM modules containing the mega-bytes of buffer memory.  You can not, they
are not there.  You object, "the buffer RAM is inside the VLSICs" good we
agree the amount of buffer is limited.  Now with a limited amount of buffer
it has to be arranged such that the data written into it and read from it
never under flows or over flows.  The only way to do this is a servo loop
that includes the disk drive motor, laser head, and demodulation circuitry
which contains the much vaunted buffer RAM.  To look simply at one aspect of
the operation, if the buffer get close to overflow, slow down the disk speed;
when the buffer gets close to underflow, speed up the disk.  And the data
being read out of the buffer has to track these variations or the buffer
will empty or fill up.  A common response is that the RAM should be made
larger to completely buffer the DACs from the drive.  I know of only one
product to use this massive overkill approach, the Technics SH-X1000 DAC.
This hi-end Japan only 'statement' product contains a 1.5MByte buffer for
incoming S/PDIF data to actually allow the data to be clocked out under
crystal control.  The unit will switch out of 'jitter free' mode if the
transport feeding it is high jitter (even 1.5MB buffers can be overflowed)
or can be manually switched out of jitter free mode for LD where the buffer
would cause loss of lip-sync.

At this point in this common disagreement the objectiviests usually counter
that us nut-ball hi-end subjectivists are quibbling over levels of clock
jitter below the threshold of audibility. "I can hear it. No you can't.
Yes I can! NO YOU CAN'T!! CAN! CAN'T!" and so on.  Meanwhile serious audio
engineers continue to improve on 'perfect sound forever' with a current
hot bed of activity being the subject of jitter and what turns out to be its
many causes.  Anyone at all interested in this topic NEEDS to get the latest
issue of Stereophile and carefully read the Robert Harley article measuring
jitter levels in a variety of products.  And then order the AES reprints he
references to learn even more, I know I will be.

Keep an open mind.  Listen for yourself.  Only YOU can decide what quality
level is good e`nuff to meet your personal needs/desires.  Digital audio is
not the done-did-deal the ad copy writers implied in 1983.  After 100 years
we are still learning ways to improve analog audio.  With a little over 25%
of that much experience with digital audio I believe there is still a thing
or two to be learned.  Continuous improvement rules.

Norman Tracy
znpt01@trc.amoco.com
Newsgroups: rec.audio