Hard Disc Player Sound Quality
 

On Thu, 22 Jan 2004 17:53:59 +0000, Ian Molton wrote:

On Thu, 22 Jan 2004 17:41:08 +0000 (UTC)
(Stewart Pinkerton) wrote:

Although its a total waste of money because any decent DAC will
eliminate jitter.

No, it won't. Your previous posts demonstrated that you have
absolutely no idea how PLLs (or any other servo system) react to rapid
fluctuations, e.g. jitter.

Depending on their design, anywhere from not at all to very badly.

We're not dealing here with a system where the frequency of the clock is
subject to change rapidly, we're dealing with a near-constant frequency
clock, with some jitter.

Good God man, jitter *is* a rapidly-changing clock frequency! Sheesh!

There is only one use for reclocking, and thats if you require a
synchronous output for things like mixing / recording. if you only
want playback, the DAC is enough, as you wont need a synchronous
output.

You completely misunderstand the criticality of a low phase-noise
clock at the point of D/A conversion.

no, I appreciate the point of having little phase noise (jitter) at the
point of conversion. however, I see no need, for reproduction purposes,
for having absolute frequency accuracy beyond that delivered by a
typical quartz oscillator.

No one is talking about absolute frequency.

having a low phase noise clock driving your DAC has sod all to do with
wether you 're-clock' the signal or not. You can achieve low phase noise
with a PLL or by reclocking (reclocking basically being a PLL with an
infinite timebase...)

No, you can *not* achieve as low phase-noise from a PLL as you can
from a free-runnijng clock. That is why one-box CD players almost
always have significantly lower jitter than outboard DACs.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Hard Disc Player Sound Quality
 

On Thu, 22 Jan 2004 17:59:21 +0000, Ian Molton wrote:

On Thu, 22 Jan 2004 17:37:57 +0000 (UTC)
(Stewart Pinkerton) wrote:


Hence, if the PLL has a bandwidth of say 100Hz (for easy lock-in),
there will be no attenuation whatever of mains-related jitter,
virtually no attenuation of PSU-related jitter, and only 20dB
attenuation of 1kHz jitter. Some top-quality DACs such as the old
Audiolab used twin PLLs, the second having a bandwidth of just 1 or 2
Hz, but this second lock only engaged with transports having clocks
very close to the nominal 44.1k data rate (within 50ppm IIRC).

be that as it may, a PLL with a long enough timebase will recover a
clock that is both jitter free and (on average) the same frequency as
the host clock, over any reasonable period.

The whole thing about jitter is that it averages out, over any
significant period to nothing. If it didnt, you'd have a frequency
drift, which is a different thing entirely. Hence as long as your PLL
has a long enough timebase, jitter is an irrelevance.

You just don't understand any of this, do you?

--

Stewart Pinkerton | Music is Art - Audio is Engineering

Hard Disc Player Sound Quality
 

On Thu, 22 Jan 2004 22:50:03 +0000, Ian Molton wrote:

On Thu, 22 Jan 2004 18:00:31 +0000 (UTC)
(Stewart Pinkerton) wrote:

the PLL bandwidth is relevant to jitter elimination, but the whole
point of a PLL is that long-term it tracks the host clock.

So what? That has *nothing* to do with short-term errors, aka jitter.

Just to be clear here...

If you agree the PLL allows one to reconstruct a local frequency that
follows the host clock, then surely you must also agree that a
buffer long enough to hold 2, maybe 3 samples, would allow one to
re-latch the digital output locked to the local frequency.

Given that, why can you not see that if your local clock *source* has a
negligible jitter, the output will be nominally jitter free?

The local clock will be a VCO, and hence will *not* have as low jitter
as a free-running clock, plus it's a plain fact that far too many
outboard DACs have poorly-designed input receivers and PLLs which
allow jitter to be transmitted from the transport with little
attenuation.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Hard Disc Player Sound Quality
 

On Thu, 22 Jan 2004 21:15:32 +0000, Chris Morriss
wrote:

In message , Stewart Pinkerton
writes
On Wed, 21 Jan 2004 09:15:07 +0000, Ian Molton wrote:

On Wed, 21 Jan 2004 08:11:37 +0000 (UTC)
(Stewart Pinkerton) wrote:

jitter should be *irrelevant* on any well designed system. Even quite
large amounts of it.

At the point of conversion, it's absolutely critical. That's the main
problem with standalone DACs for CD.

The point being, of course, that any *WELL* designed system will use a
good PLL and thus eliminate the problem.

Unfortunately, these are thin on the ground in high-end audio........

Heck, some of those clowns don't even put in the reconstruction
filter! No, really, check out AudioNote.....................

BTW, a PLL *reduces* the jitter problem, only a synchronous master
clock can *eliminate* jitter.

A proper dual PLL will render it totally harmless. A PLL with a short
loop time constant for the data receiver clock, and then a PLL with a
long time constant to produce the DAC clock should do it.

Agreed that this will reduce jitter to an acceptable level, but it
will not *eliminate* it, as Ian Molton is claiming.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Hard Disc Player Sound Quality
 

On Thu, 22 Jan 2004 22:51:43 +0000, Ian Molton wrote:

On Thu, 22 Jan 2004 18:03:45 +0000 (UTC)
(Stewart Pinkerton) wrote:

So does his technobabble............

Actually, that needs a *lot* of work!

I wasnt going to say anything but didnt you just admit to being wrong
*despite* your technobabble in a certain other thread?

I guess mine isnt the only one...

The difference is that I both understood my error, and was happy to
admit it.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Hard Disc Player Sound Quality
 

On Thu, 22 Jan 2004 21:48:44 +0000, Chris Morriss
wrote:

In message , Stewart Pinkerton
writes
On Wed, 21 Jan 2004 09:15:07 +0000, Ian Molton wrote:

On Wed, 21 Jan 2004 08:11:37 +0000 (UTC)
(Stewart Pinkerton) wrote:

jitter should be *irrelevant* on any well designed system. Even quite
large amounts of it.

At the point of conversion, it's absolutely critical. That's the main
problem with standalone DACs for CD.

The point being, of course, that any *WELL* designed system will use a
good PLL and thus eliminate the problem.

Unfortunately, these are thin on the ground in high-end audio........

Heck, some of those clowns don't even put in the reconstruction
filter! No, really, check out AudioNote.....................

BTW, a PLL *reduces* the jitter problem, only a synchronous master
clock can *eliminate* jitter.

Provided that the jitter is less than (say) 25% of the data bit period,
then a two-loop PLL with a fast loop feeding a clock to the data
receiver, and a slow PLL then feeding a clean clock to the DAC, will
eliminate any problem.

It may reduce the problem to an inaudible level, but it won't
*eliminate* it. That requires a single master clock, a la professional
transmission protocol SDIF-2.

Of course, if the short term jitter is greater than 50% of the bit
period then there's no chance!

I use the CS8414 data receiver and CS4396 DAC at work at the moment, and
have no jitter problem. The SPDIF signal from the CD sources at work,
and my own CD63 and CD52SE have jitter less than 25% of the bit period.
(That's checked by looking at the eye diagram of the data stream.)

--

Stewart Pinkerton | Music is Art - Audio is Engineering

Hard Disc Player Sound Quality
 

On Thu, 22 Jan 2004 22:51:37 +0000, Ian Molton wrote:

On Thu, 22 Jan 2004 21:48:44 +0000
Chris Morriss wrote:

Provided that the jitter is less than (say) 25% of the data bit period,
then a two-loop PLL with a fast loop feeding a clock to the data
receiver, and a slow PLL then feeding a clean clock to the DAC, will
eliminate any problem.

It *may* eliminate the *audible* problem, but it certainly won't
elimminate jitter!

Of course, if the short term jitter is greater than 50% of the bit
period then there's no chance!

Ah, the voice of reason.

Hey Stewart... time for the *second* retraction of the day?

Of course not, since these systems, as I previously stated, merely
*attenuate* jitter, they do *not* eliminate it. For that, you need a
single master clock controlling the entire process.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Hard Disc Player Sound Quality
 

On Fri, 23 Jan 2004 08:29:52 +0000 (UTC)
(Stewart Pinkerton) wrote:

I guess mine isnt the only one...

The difference is that I both understood my error, and was happy to
admit it.

The difference is that you *were* in error. I am not.


--
Spyros lair: http://www.mnementh.co.uk/ |||| Maintainer: arm26 linux

Do not meddle in the affairs of Dragons, for you are tasty and good with ketchup.

Hard Disc Player Sound Quality
 

On Fri, 23 Jan 2004 08:29:52 +0000 (UTC)
(Stewart Pinkerton) wrote:


The local clock will be a VCO, and hence will *not* have as low jitter
as a free-running clock,

There is nothing that says it *cant* though. just because one given
design doesnt achieve the goal doesnt mean the concept is flawed.

plus it's a plain fact that far too many
outboard DACs have poorly-designed input receivers and PLLs which
allow jitter to be transmitted from the transport with little
attenuation.

Im sure thats the case. nontheless it has no bearing on my specific
point.

--
Spyros lair: http://www.mnementh.co.uk/ |||| Maintainer: arm26 linux

Do not meddle in the affairs of Dragons, for you are tasty and good with
ketchup.

Hard Disc Player Sound Quality
 

On Fri, 23 Jan 2004 08:29:53 +0000 (UTC)
(Stewart Pinkerton) wrote:

Of course not, since these systems, as I previously stated, merely
*attenuate* jitter, they do *not* eliminate it. For that, you need a
single master clock controlling the entire process.

bull****. A single master clock may give you a nice, precise reference
so that synchronising your sources is easy, but it doesnt (necessarily)
have any impact on jitter.

--
Spyros lair: http://www.mnementh.co.uk/ |||| Maintainer: arm26 linux

Do not meddle in the affairs of Dragons, for you are tasty and good with
ketchup.