26 Feb
2007
26 Feb
'07
2:43 p.m.
Frank Barknecht wrote:
Hey, that's actually the first time I read about 1-bit recording and
at first I thought you were joking or had a typo. But you weren't and
hadn't.
It works pretty well and is easy to implement in silicon.
Back in college, using a few square inches of printed circuit board, a
soldering iron and a handful of components, I made two little devices
whose only purpose in life was to:
1. Grab an analog input and transform it into a 1-bit digital signal
2. Grab the 1-bit digital signal and convert it back to analog
Not very useful in practice, but a fun project for a boring week-end
afternoon. The toys were so simple, they didn't even have a clock, the
transitions between 1 and 0 happened whenever the proper conditions were
met (there was a capacitor somewhere that was either charging or
discharging very quickly, with the average voltage trying to follow the
analog input, and it was sending to the digital output the information
of either "I'm charging" or "I'm discharging"). I guess the
digital
"carrier" was somewhat self-stabilizing (somewhere in the MHz range I
guess).
Those of you familiar with electronics can probably figure out the rough
design of the scheme already.
The sound quality was pretty damn good too, which is somewhat odd given
the rudimentary technology.
With minimal effort, more complex converters can be made that can offer
much better quality. Mine was a hack.
Single-stage, 1-bit sigma-delta converters are in
principle
imperfectible. We prove this fact. The reason, simply stated, is that,
when properly dithered, they are in constant overload. Prevention of
overload allows only partial dithering to be performed. The
consequence is that distortion, limit cycles, instability, and noise
modulation can never be totally avoided.
Interesting.
--
Florin Andrei
http://florin.myip.org/