In article , Stewart Pinkerton
wrote:
On Sun, 31 Aug 2003 18:57:37 +0100, Chris Isbell
wrote:


Could you possibly explain why a separate DAC is a very bad idea,
please? (I have just purchased one!)

Jitter. The CD system was never intended to have separate transports and
DACs, so the embedded clock in the S/PDIF datasteam is not robust, and
is prone to adding jitter. Not a problem for a well-designed DAC, but
far too many so-called 'high end' DACS have input receivers which are
quite stunningly incompetent at suppressing jitter.

Agree with the above! This is one of the reasons I am wary of statements
about whether or not "transports differ in sound". In isolation, the
transport can't have a 'sound' as it is outputting a series of binary
values, not an analog waveform you can amplify and listen to. Hence the DAC
section performance is critical even when trying to assess the
'performance' of a transport.

I don't tend to hear differences when I change from one transport to
another, using the same DAC. However this may be due to my being
cloth-eared, or due to the DACs I use being particularly good as
suppressing source jitter, etc. Hence it leads me to doubt that "all
transports sound different", but accept that in some cases at least,
changing transport may affect the results. :-)

However the real point here, for me, is that it is the task of the circuits
that *follow* the reading of the raw data from the CD to prevent jitter,
etc, from adversely affecting the final sound performance. Hence if I found
that transports sounded different, using the same outboard DAC, I'd be just
as tempted to argue that the *DAC* was failing in its duties as I would to
worry that the transports were not working as they should.

FWIW I suspect that the Meridian 200 transport I have may well be providing
an SPDIF output which has a lower jitter, etc, than the Pioneer CDRW
sitting next to it. However the Pioneer plays discs that the meridian
refuses to track, and I also have the impression that the Meridian outboard
DACs do a good job of squashing any differences in jitter effects between
the two transports. Hence I tend to use the Pioneer as much as the 200 as a
transport. In the end, I think it is the performance of the *system* that
matters. :-)

Slainte,

Jim

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