Re: What's the use of a 192 kHz sample rate?

In article <ltudnZJaF7ZP_77VnZ2dnUVZ_r2nnZ2d@[EMAIL PROTECTED]
>,
Arny Krueger <arnyk@[EMAIL PROTECTED]
> wrote:

>> He could not find anything strange, the high end CD
>> player has FIFOs, which keep the jitter constant and
>> minimum (low end is different story, but audiophiles
>> use high end).
>
>In fact all CD players have a FIFO or something like it, which reduces
the 
>natural high jitter of the data coming off the CD.

Yup.  There has to be, because the data coming in from the CD and its
low-level demodulator has to be buffered up and fed into a two-level
cross-interleaved Reed-Solomon error-correction decoder.  The data
coming out of the error correction logic is at a significantly lower
bit-rate than the raw data coming in from the CD read assembly, and
the bits are in a very different ordering.

There's also quite a bit of "wow" in the rate of the data being read
from the CD... the CD's motor speed is being adjusted dynamically "on
the fly" in order to keep the amount of data in the de-interleaver and
Reed-Solomon decoder from rising too high (which would overrun the
buffer memory) or too low (which would result in the data stream to
the DAC chip running out).

Every single-box CD player I know of, from the very earliest days
until now, has incor****ated this sort of buffering and FIFO in its
decoder chip, and has clocked the data into its DAC-chip based on a
signal from an onboard quartz oscillator.  As long as the quartz
oscillator is stable (good power, adequate protection against
microphonics) there should be little jitter in the timing of the
digital-to-analog conversion.

Two-box playback systems (a CD trans****t with the Reed-Solomon
decoder, and a separate DAC-box or A/V amplifier, connected via S/PDIF
or a similar digital pathway) actually have a harder job of it,
because the DAC-box doesn't have direct access to the stable quartz-
oscillator signal that drives the Reed-Solomon decoder.  Such setups
must "recover" stable clock timing from the incoming S/PDIF or other
digital-audio signal, and this is a nontrivial process and is
sometimes done rather badly.  This is a case of "pay more, and get
more problems rather than less".

-- 
Dave Platt <dplatt@[EMAIL PROTECTED]
>                                   AE6EO
Friends of Jade Warrior home page:  http://www.radagast.org/jade-warrior
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