From: sklower@diva.Berkeley.EDU (Keith Sklower)
Newsgroups: rec.audio
Subject: Re: PCM encoders
Date: 7 Oct 92 01:02:12 GMT
Organization: /etc/organizaton

In article <BvFBvF.B5t@cantua.canterbury.ac.nz> glassey@elec.canterbury.ac.nz (Robert Glassey) writes:
}I'm interested in PCM encoders for recording digital sound on
}video recorders.... I'm interested in ...  something to use ... for
}either digital audio, or computer backup.

There were two formats commonly in use during the past decade;
one a consumer format, the other intended for professional use.
You can sometimes see a consumer unit offered for sale here in the US
for around $500.  I don't know if anybody is still manufacturing
new consumer units for sale.

}... Did they even make them for PAL systems?

yes.  

}I gather they used 14 bits, and 44.1kHz sample rate. What
}error correction techniques did they use?

The sony system also allowed 16 bits but with reduced error
detection facilities.  The professional system is still in use
to this day as the standard means of conveying the digital audio
information to the pressing plants.  The both versions used six
samples per scan line.
The professional version would do bitwise exclusive or's between 3 pairs
of the samples, and had additional CRC bits, so that error correction
was possible.

}What are the error characteristics of a video tape?
}Is only the luminance used?
}Does it require a special B&W recorder with a wide bandwidth?
}What is the bandwidth used?
}How is the signal modulated?

Only luminence was used, and neither required a special B&W recorder.
People using the professional format were encouraged to use U-Matic
(and that is demanded for what you send to the pressing plant.)
Some of the consumer versions could use regular VHS in the slowest speed
and still get by.
The signal could be displayed on a normal TV set; I'm not a TV kinda
guy so I can't give you the technical details.  What it looked like
where a bunch of black and white (or very light gray) squares.  Apparently
there was a pulse at maximum white somewhere towards the end of the scan
line to defeat gain-control circuitry.

}Is the tape speed controlled, or do you get lots of 'wow'?
}What chip sets are about to do the error correction,
}interleaving & interpolation?
}Anyone out there got one or used one?
}What is your impression of them? What are their limits?

I've used a realtively inexpensive consumer version (the PCM-501ES).
It seemed a heck of lot better than any cassette recorder I had ever
encountered at the time.  The next step up from mine was the PCM-601ES
which allowed external digital I/O, and there is no reason why you
couldn't use that with a modern oversampling high quality external
A/D converter (such as the apogee A/D 500)
I had a chance to talk to one of the engineers for WGBH boston, who
claimed that he used two of the consumer units (PCM-F1's) to transmit
the sound live from a concert of the Vienna Philharmonic back to the US.
(Over a standard satellite video feed).

Bill Vermillion or Rick Karlquist could certainly have supplied more
interesting stories and details than I have, having used the adapters
more extensively.

It may be possible to wheedle some information out of sony about
their chipsets, but given the many, many, hours that would be
required for you to re-engineer one of the units, I'ld suggest
getting a consumer DAT . . . .
Newsgroups: rec.audio,sci.electronics