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Subject: Re: USB Design. Need advice.
Date: Sat, 28 Dec 2002 20:25:55 +0100
NNTP-Posting-Date: Sat, 28 Dec 2002 20:25:56 MET
Dan McDaid wrote:
> The two vinyl disks that
> are put onto each turntable respectively, are pressed with some sort of
> waveform that can be interpreted digitally as a timeline. (waiting on a
> replacement LP from Stantons FinalScratch - in post so I can see how it
> works and rip it off - cheaper than having my own vinyl pressed several
> times until I got the right idea!).
Would you need a timeline - or only a signal that says how fast you are going
forward or backward, and the speed?
The latter is not hard to achieve with a quadrature stereo signal. If the left
channel leads the right channel, you are moving forward. If not, you go
backward. And every cycle is a millisecond or so.
You could do this in mono as well. Perhaps a signal like _-__-- repeating.
Harder to detect than the quadrature, but it means looking for the quick signal,
and if a high or low signal follows.
HOWEVER the wave shape coming from the turntable will not be a nice square wave.
It could also be done with tones. Three tones in succession, and toe-da-die
meand going forward. Problem is you only find out about reversals after such a
period. And you must keep track where in the toe-da-die cycle you are or you
miscalculate speed :)
If you want to embed absolute time, better to do that in some subchannel, if you
can stand low resolution.
Decoding this will be the hard part. The A/D and D/A converters are the off the