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Lang asks Tech Heads

Subject: Lang asks Tech Heads
From: Marty Michener <>
Date: Wed, 06 Nov 2002 09:43:27 -0500
At 08:55 AM 11/6/02 -0500, you wrote:
>I have a question for all the tech heads:
Hello Lang!

I'll let the head tech (Walt) answer most of this, but my take is: the
synchronization you will probably be looking for will not be there.  Ears
can hear, according to experiments in the 1960's, time differences of about=

10 to 50 microseconds, depending on to whom you talk.  The sharpest coin
click you could record would not give sufficient coincidence to make the
later synchronzation possible, especially as it is recorded in digital
form, notorious for ruining arrival times.

>I want to experiment with some 4-channel recording using a special
>"quad-SASS" setup, however I do not have a four channel field recorder. In
>the short run, I'd like to try doing this using my two Sony TCD-D10 Pro DA=
T
>recorders, each having two channels.
>
>Has anyone tried this? If I record with both recorders, I could coordinate
>them by making a broadband "tick" at the beginning by tapping two coins
>together at a point equidistant from the two mike setups. Later, when the
>two stereo recordings are inputted into my computer (using direct digital
>S/PDIF transfer), I could slide the two stereo tracks to exactly overlap t=
he
>waveforms of the introductory "tick". This should coordinate the four
>tracks, at least at the beginning of the recording.
>
>My question concerns drift.

The head tech has already made several posts about drift, regarding his
head Mac and his PortaDisc and/ or DAT recorder.

Real life studios synchronize all their stuff with what used to be called
"genlock", that is, one machine did all the timing, and the others were
locked to it.  This was mostly to synch TV rasters, which need to be locked=

to less than one microsecond for the picture scan lines to appear at the
same point.

>For instance, if I record for ten minutes straight, is it likely that the
>two recordings would drift in the time domain due to slight differences in
>sampling rates? If this happens, it could render the technique useless.
>
>How does a DAT recorder generate sampling rate?

with an internal clock.

>Would two DAT recoders of
>the same make and model have absolutely identical sampling rates, or would
>there be some inherent variation, however small? If so, then would this
>variation be enough to cause significant drift between the two recorders
>over a 5-10 minute timespan?

They might drift apart as much as a sample every ten to thirty seconds, I
would guess.


>Has anyone tried this? I think I remember someone posting a note about thi=
s
>some months ago.
>
>Lang

We bought for home use, as I have posted previously, a Teratech (sp.?)
eight channel sound card for my son's PC, if I recall, two years ago it ran=

about $ 499.  It was chosen for the very reason that all eight channels are=

strobed to take a sample, at 96 kHz, 24 bit, exactly at the same time
point.  Cheaper models, as I recall, strobe the channels sequentially, so
sounds that later are regarded as synchronized are actually offset by a
small, constant time error.

best,


Marty Michener
MIST Software Associates
PO Box 269, Hollis, NH 03049


EnjoyBirds - software that migrates with you.  Now shipping.




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