Other: Big Buck CD Players

[Frank Weil]

> > The audio rags make far to much of a fuss about the difference of
> > sound between CD players.  I guess it's because they have to justify
> > their existence by talking about a "new" topic every issue, so they
> > follow all the latest D/A converter black magic, and make a big deal
> > out of it... but frankly, mid range CD players are mostly within 1% of
> > each other in terms of sound quality, and the high end models are
> > within about .1% of each other.
>
> Well, the signal processing I learned recently as part of a digital image
> processing class gave me a greater appreciation of the problems of
> digital audio.  But like I said in another message, CD players aren't
> totally digital devices; many people seem to underestimate this, and come
> to the conclusion that "all CD players must sound the same" as a result.

I will agree that at the high end, CD player differences are more
subjective.  However, not all CD players have the same amount of
analog and digital pathways.

When the signal is read off the CD, it is a single bit stream with the
left and right channels intermixed.  Given sufficient error
correction, the signal is exactly the same on every CD player.  At
this point, there are two different schemes for translating this
signal into separate left/right analog signals:
  1) Separate the channels, perform D/A conversion, do any signal
     processing.  CD players of this type usually advertise as being
     "14 bit" or "16 bit" or some number like that.
  2) Do all the processing on the digital bitstream, perform D/A
     conversion.  This scheme is usually called "single bit".

There are lots of variations on these two schemes, of course.  In
scheme (1), many tricks like oversampling are done to help the D/A
process since the digital signal is barely high enough to be above an
acceptable Nyquist rate.  The quality of the D/A conversion can have a
big impact on the "color" of the sound that is produced.

In scheme (2), a big factor on the sound is the signal processing that
is done in the microprocessor on the digital bitstream.  For the D/A
conversion, the processor creates a high-frequency stair-step
approximation of the desired analog waveform.  This quantized signal
is then simply passed through a low-pass filter to smooth out the
jaggedness of the quantization.  The filtering step does have an
effect on the output sound since the filter adds its own colorization.
That is why, for example, Carver has a high-end CD player which uses
analog tubes ("valves" for you guys on the other side of the pond) to
give a "mellower" sound to the low-pass filtering.

I have a Carver single-bit CD player and I am extremely happy with it.
I don't remember the model number, but it is the one with the non-tube
output filter stage.  I think that Carver's "Digital Time Lens"
processor sounds excellent and I tend to leave it on all the time.

Frank

--
 ==============================================================================
Frank Weil | frankw at comm.mot.com | phone: (847) 576-3110 | fax: (847) 576-3240

Q: What happened then?
A: He told me, he says, "I have to kill you because you can identify me."
Q: Did he kill you?
      -- Disorder in the Court: a Collection of 'Transquips' by Richard Lederer