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Topic: Dither explained, by Nika (Read 12422 times) previous topic - next topic
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Dither explained, by Nika

Reply #25 –
Quote
Originally posted by Frank Klemm

Hope this compiled from 1.01j20, not from 1.01j11...13. Call mppdec16 and look
for the range proposal of --dither:

  old: 0.0-1.7
  new: 0.00-1.00

It's new, the range is 0.00-1.00.

Dither explained, by Nika

Reply #26 –
Pio2001, Frank,


what Pio2001 is suggesting is like DSD, only with more bits. OK, so DSD noise-shapes the error signal, rather than "just" adding high frequency dither, but I'm sure at the level Pio2001 was proposing the idea (i.e. a very basic explanation), he wasn't worry about such issues - and what he was saying, in a very basic sense, was right.

His system exists too - it's called DSD-wide, uses 8-bits and runs at 2.something MHz. It's used in the production of SACDs, and (unlike the 1-bit signal which goes onto the final disc) is theoretically perfectable. The low-pass starts at 100kHz and is quite gentle.

Cheers,
David.
http://www.David.Robinson.org/

Dither explained, by Nika

Reply #27 –
Do you mean that DSD uses it's own "quantization" (if such a word exists in DSD) noise as a dither :eek: ? I had never thought about it !

Dither explained, by Nika

Reply #28 –
Quote
Originally posted by Pio2001
Do you mean that DSD uses it's own "quantization" (if such a word exists in DSD) noise as a dither :eek: ? I had never thought about it !


For a perfect quantization process you need at least 2 LSBs dither. With a 1 bit system you can't add 2 LSBs dither.
for a 2 bit system it reduces FS level by a factor of 3 (9.54 dB).

So you can't dither a 1 bit system properly. You need the help
of the noise shaping process (noise shaping has nothing to do
with dither, see http://www.uni-jena.de/~pfk/mpp/Dieter.html).
But these only reduces distortions, and some amount remains.

You can construct signals which can't be reproduced by DSD,
they sound very different from the original. With PCM this is
not possible.

With 2.88 MBit/s you can have a system with 96 kHz/16 bit
with a flat response until 38 kHz, a gentle slope down to
-70 dB until 58 kHz using some noise shaping to reach
134 dB of SNR.

This is half the data rate of DSD, distortion free, easier to handle,
double the frequency response I need, a impulse response of
80 µs.

If jitter is a problem of digital audio, also note that DSD is
by about a factor of 1:1000 more sensitive to jitter than PCM.
--  Frank Klemm

Dither explained, by Nika

Reply #29 –
I'd like to read about how DSD - SACD works.
I've already read many times that each bit meant that the signal should go up or down. But with an around 2 Mhz rate, it would mean about 50 bits each 40000th of a second. Therefore, in order to be able to code a full scale 20 kHz wave, the size of the step must be at least 1/50th of full scale, which would mean no more than 6 bits of resolution (2^6=64)

Therefore this description of SACD must be wrong somewhere...unless there is some strong ultrasonic dither at work...Is that it ?
 

Dither explained, by Nika

Reply #30 –
Quote
Originally posted by Pio2001
I'd like to read about how DSD - SACD works.
I've already read many times that each bit meant that the signal should go up or down. But with an around 2 Mhz rate, it would mean about 50 bits each 40000th of a second. Therefore, in order to be able to code a full scale 20 kHz wave, the size of the step must be at least 1/50th of full scale, which would mean no more than 6 bits of resolution (2^6=64)

Therefore this description of SACD must be wrong somewhere...unless there is some strong ultrasonic dither at work...Is that it ?


DSD uses 64 times the sample frequency like the CD and
and exactly 1 bit per sample. Normally this would produce
a SNR of 25.8 dB relative to 44.1 kHz. The 120 dB are achieved
via really heavy noise shaping. To my mind so heavy noise shaping makes a lot of problems, also so called 1-bit-Converter
often use 7, 9 or 11 steps (instead of 2) to have less problems with noise shaping.

Note, that even when DSD have some advantages, this will be
killed by technical high end gadgets like digital controlled
loudspeakers, sound field synthesis, because they must be
converted to normal PCM before you can do such nice things.
--  Frank Klemm