I am aware that a transport dosen't have a filter but a dac does and thats
where the digital signal goes to. To perform at its optimum it needs a clean
digital signal. On a scope you can see how clean the signal is.

I do not know what experience you have of listening to CD transports but I can
assure you they sound different and there must be reasons for that.

"Derbydrummer" wrote in message

I am aware that a transport dosen't have a filter but a dac does and
thats where the digital signal goes to. To perform at its optimum it
needs a clean digital signal. On a scope you can see how clean the
signal is.

I do not know what experience you have of listening to CD transports
but I can assure you they sound different and there must be reasons
for that.

I assure you that if you do naive listening tests, everything sounds
different, even two identical CD players.

In article ,
Derbydrummer
wrote:
I am aware that a transport dosen't have a filter but a dac does and
thats where the digital signal goes to. To perform at its optimum it
needs a clean digital signal. On a scope you can see how clean the
signal is.

Agreed. However your description above omits various processes which are
performed in between the physical reading of the disc to recover the
channel data steam, and the DAC. These tend to include reclocking and
reshaping of the data, and conversion of the raw serial binary into a
series of words which are then digitally buffered, error corrected, etc,
etc.

Hence commenting that the raw channel data stream may vary from one
transport to another does not establish if/when this may have an audible
effect. The raw signal only has to be 'clean' enough for the intermediate
processes to be carried out in a reliable manner. My experience with this
is summarised below.

I do not know what experience you have of listening to CD transports but
I can assure you they sound different and there must be reasons for that.

I can only give my own experience. So far as I am concerned it is as
follows:

I currently regularly use four 'transports' to play CDs. A meridian 200, a
Quad 67, a Pioneer CDRW, and a low-quality DVD-V/VHS player. I have
a meridian 263 DAC and a meridian 563 DAC. I have used various other
players in the past, with results broadly in line with what follows.

I have experimented with using the 263 and 563 to listen to the digital
outputs of the above four transports. So far as I can tell, they are
normally indistinguishable. i.e. I can't normally tell one transport from
another when using the same DAC. The only caveats on that which I have
discovered a

1) Some discs show an audible level of faults. (I had some that sufferred
from the PDO brown rot. These were quite useful for test purposes before I
had them replaced.) The different transport/DAC combinations sometimes mask
or deal with these gross errors in audibly different ways. However in
statistical terms here I am talking about less than 1 percent of the CDs I
have owned.

2) The cheap DVD-V/VHS player makes mechanical noises sometimes near the
start of playing CDs. This is noticable and can be distacting. The audio
via the DAC does not seem to be affected, though.

I've had various other people listen and like myself they don't seem to
hear any systematic differences related to the transport in use.

However if I use the Quad and the DVD-V/VHS via their own DACs, some
differences are audible. FWIW I'd say the DAC/audio sections of the
DVD-V/VHS player were dire! This seems to be a reflection on the
electronics *after* the actual transport has recovered the data
from the CD, though, as the player sounds excellent to me via
the meridian 263 DAC.

It seems fair enough to say that *some* transports may produce some audible
differences with *some* discs. However I can assure you that my own
experience over the last 20 years is that the transport generally has
little or no audible effect.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

On 30 Aug 2003 20:43:24 GMT, (Derbydrummer)
wrote:

I am aware that a transport dosen't have a filter but a dac does and thats
where the digital signal goes to. To perform at its optimum it needs a clean
digital signal. On a scope you can see how clean the signal is.

If you actually understood how DACs work, you'd be aware that:

1) A separate DAC is a *very* bad idea.

2) A *good* DAC will minimise any incoming jitter to the extent that
all properly functioning transports will produce an audibly identical
output signal from the DAC.

I do not know what experience you have of listening to CD transports but I can
assure you they sound different and there must be reasons for that.

Yes, it's called a crap DAC! Regrettably, idiotic 'high end' dealers
seem to think that incompetent DACs which do *not* suppress incoming
jitter are 'more transparent'. Such is the incompetence of the 'high
end' industry, but it need not prevent the rest of us from doing the
sensible thing, and buying a standalone player.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sun, 31 Aug 2003 11:32:30 GMT, (Stewart
Pinkerton) wrote:

If you actually understood how DACs work, you'd be aware that:

1) A separate DAC is a *very* bad idea.

2) A *good* DAC will minimise any incoming jitter to the extent that
all properly functioning transports will produce an audibly identical
output signal from the DAC.

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

Thanks,


--
Chris Isbell
Southampton
UK

On Sun, 31 Aug 2003 18:57:37 +0100, Chris Isbell
wrote:

On Sun, 31 Aug 2003 11:32:30 GMT, (Stewart
Pinkerton) wrote:

If you actually understood how DACs work, you'd be aware that:

1) A separate DAC is a *very* bad idea.

2) A *good* DAC will minimise any incoming jitter to the extent that
all properly functioning transports will produce an audibly identical
output signal from the DAC.

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.

In a standalone player, a single low-noise free-running master clock
placed close to the DAC chip controls the entire system, leading to
lower jitter than is possible from a separate DAC with it's PLL clock.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Mon, 01 Sep 2003 00:13:46 +0100, Chris Isbell
wrote:

On Sun, 31 Aug 2003 21:09:45 GMT, (Stewart
Pinkerton) wrote:

[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.

In a standalone player, a single low-noise free-running master clock
placed close to the DAC chip controls the entire system, leading to
lower jitter than is possible from a separate DAC with it's PLL clock.

Thanks. So if the DAC regenerates the digital signal with its own
clock then jitter should not be a problem?

Correct, although this is extremely rare. Your SRC does however do
exactly that.

My DAC just happens to be
preceded by a sample rate converter; it's a Behringer SRC2496.
(Fortunately it's not a high end DAC so it may be reasonably competent
in handling jitter on the S/PDIF data stream. ;-)

If the SRC has a good clock, then you may end up with a good system.

If there were a problem, how would it affect the sound?

You would hear a slight 'smearing' of the sound, as jitter generates
FM distortion, just like wow and flutter but generally at higher
frequencies.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

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

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html