Date:         Sat, 27 Sep 2003 10:09:51 +0000
Reply-To:     Association for Recorded Sound Discussion List
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Sender:       Association for Recorded Sound Discussion List
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From:         Don Cox <[log in to unmask]>
Subject:      Re: Optical Groove Digitization
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On 26/09/03, Rob Spencer wrote:

> As always, Dr. Goldman brings up points worth pondering, especially as
> regards the reproduction of coarse-grooved records. Wouldn't it be
> nice to have a turntable/arm combination specifically engineered for
> 78 playback, as opposed to microgroove? With proper anti-skating, at
> least?

A well engineered setup should be suitable for both. I find the main
requirement for 78s is careful mounting of the turntable to avoid rumble
and feedback.


> More interesting is the question of digitization of the signal. It
> seems to me that the process of producing a highly accurate 3-D
> digital image of the surface of a record does not digitize the signal,
> merely the physical analogue of the signal as represented by the
> groove on the record.

It is true that it doesn't directly digitize the vibrations in the air.
This is also the case when a tape is digitized.


> In fact, the signal need not be digitized at all with this process,
> whether the virtual groove is tracked virtually or used to produce a
> new copy of the record for traditional playback (both options have
> been discussed on this list). It can be kept in analog form. One may
> argue that digitizing the record surface perforce digitizes the
> signal, but if the accuracy is high enough it seems to me that there
> would be no effect on the signal itself.

The point here is that complaints about digitized sound are based on its
inaccuracy. If the A->D conversion is extremely accurate and
fine-grained, and the D->A conversion is equally good, then the final sound
will be acceptable.

Conversions made with early digital technology or with cheap
consumer-grade equipment (such as typical computer sound cards) are
likely to be grossly inaccurate.


>
> In any event, the typical pre-tape 78 was recorded direct to disk, more
> or less, so unless there is access to the original metal parts or an
> intermediate form, the record itself is the lowest-generation copy
> available, so we are faced with the necessity of tracing its groove in
> one way or another. In theory, the process discussed herein would seem
> to allow the most accurate extraction possible of the information
> represented by the groove. At the least, it would allow the
> reconstruction of a mint copy of any record that has a groove that is
> pristine at some level all along its length. This last consideration
> alone is enough to justify it for me.

The advantage of a digital representation is that you can make exact
copies of it and apply complicated processing. The disadvantage is that
accurate conversion to and from analogue is very difficult.

This applies to images as well as sound.

Regards
--
Don Cox
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