[]|[ GorE]

Hi,
I have a Panasonic DVD player with an audio jitter of 170ps measured done by a HiFi magazine.Now,the magazine doenst mention if the measurements were done using the units coaxial or optical out.So,does jitter vary depending upon the the transport medium used ? The players connected to a Panasonic Digital receiver rated 60Watts each. And what effect does this jitter have on the overall sound quality.

For comparison,Sterophile's measured jitter of the ipod is 225 ps which they say is better than most cd players out there.So where does my cheap Panasonic universal player stand amongst the croud ?

Thanks.

 

[thomaspf]

The jitter measurement was done by looking at the analog output

CD players or the Ipod for that matter have a huge advantage over an outboard DAC connected via S/PDIF.

You can clock the DAC directly from a crystal oscillator and asynchronously control the delivey of data from a CD or hard drive to the DAC.

With an outboard DAC the converter chip is being clocked by a signal that is recovered from from the S/PDIF signal. This process introduces much higher jitter level unless you have a carefully designed dejitter circuit in the DAC.


Hope this helps

Thomas

 

[TheSloth]

Quote:

Originally Posted by thomaspf This process introduces much higher jitter level unless you have a carefully designed dejitter circuit in the DAC. Hope this helps Thomas

I think saying it introduces 'much' jitter is an overgeneralisation, and 200ps at least in my book is not a lot. It is a small amount that I'd rather not have, but it's not as relevant as 200ns...

 

[thomaspf]

Where does the 200ps come from?

 

[TheSloth]

Quote:

Originally Posted by thomaspf Where does the 200ps come from?

A generic amount of total jitter from the final analogue out of a good DAC, connected to a good transport via an optical cable.

 

[thomaspf]

Quote:

Originally Posted by TheSloth good DAC, connected to a good transport

emphasis added

So coming back to the original question. What constitutes a good transport and what makes a good DAC.

The Zhaolu has no jitter rejection beyond the receiver chip which is speced to provide some jitter attenuation to the tune of 350ps.

Which transport or soundcard is much lower than that 200ps so that when you combine the two with an optical cable you actually get less or equal than 200ps in the converted analog signal.


Cheers

Thomas

 

[TheSloth]

Quote:

Originally Posted by thomaspf emphasis added So coming back to the original question. What constitutes a good transport and what makes a good DAC. The Zhaolu has no jitter rejection beyond the receiver chip which is speced to provide some jitter attenuation to the tune of 350ps. Which transport or soundcard is much lower than that 200ps so that when you combine the two with an optical cable you actually get less or equal than 200ps in the converted analog signal. Cheers Thomas

Ok my number was slightly low. Apple Airport Express to MF XDAC V3 = around 250ps (check the exact number in stereophile, but I'm very close). Computer optical out to HeadRoom Max DAC (Desktop) = also around 250ps. These are not the cheapest DAC's, but they are hardly 'high end' in the head-fi sense, cose wise. The transports are, well, cheapo.

 

[thomaspf]

If I am not mistaken both the Musical Fidelity XDAC V3 and the HeadRoom Max DAC happen to be DAC that use an asyhronous sample rate converter and a local clock.

This means the jitter you see comes from a local crystal clock and is mostly independent from the source. This method does of course introduce other artefacts.

Unfortunately none of this probably applies to the Zhaolu which does not have an ASRC chip for better jitter rejection.

Cheers

Thomas

 

[TheSloth]

Quote:

Originally Posted by thomaspf If I am not mistaken both the Musical Fidelity XDAC V3 and the HeadRoom Max DAC happen to be DAC that use an asyhronous sample rate converter and a local clock. This means the jitter you see comes from a local crystal clock and is mostly independent from the source. This method does of course introduce other artefacts. Unfortunately none of this probably applies to the Zhaolu which does not have an ASRC chip for better jitter rejection. Cheers Thomas

I'm not sure why you keep going on about the Zhaolu? That's nothing to do with this thread?! The OP just wanted to know how his source stacked up in terms of jitter...

 

[thomaspf]

The Zhaolu is just an example of a simple DAC with no jitter rejection. Probably very similar to the Panasonic receiver that the original poster is using.

The jitter measurement on the Panasonic were done using the local analog output and cannot be used to predict what the jitter on a receiver connected via S/PDIF will be. Many receivers do not use reclocking circuits since that usually impacts lip-sync.

I too have been trying to understand how your postings help the original question but I can be slow at times so please bear with me.

Cheers

Thomas

 

[Garbz]

Quote:

Originally Posted by thomaspf The jitter measurement was done by looking at the analog output CD players or the Ipod for that matter have a huge advantage over an outboard DAC connected via S/PDIF. You can clock the DAC directly from a crystal oscillator and asynchronously control the delivey of data from a CD or hard drive to the DAC. With an outboard DAC the converter chip is being clocked by a signal that is recovered from from the S/PDIF signal. This process introduces much higher jitter level unless you have a carefully designed dejitter circuit in the DAC.

Finally someone on this board is dancing to my tune

Though looking at the analogue out isn't the only way to analise jitter. It's just one of many, and the easiest since it doesn't require external hardware or disassembling the unit.

Jitter is very audible. Some would argue even 3ps of jitter is audible. I personally don't stand to thoes claims but a hundred or so ps most definitly is. This usually presents as anything from slight harshness, to brightness, to full blown distortion in the treble.

Use the search function for a "jitter test track" someone posted on my behalf a copy of a stereophile jitter demonstration track in the DIY forum. A 1khz tone, and then the same tone with a lot of jitter added. This should give you an audible example.

 

[thomaspf]

I tought the original Dunn paper had established ~20ps as the threshold were the distortion introduced by the jitter is roughly equivalent to changing the lowest order bit in a sample.

This was calculated for a 16/44.1 signal. For higher frequencies you need to be stricter.

Last time I loked into this the lowest measured jitter by Atkinson in a DAC was around 120ps.

Cheers

Thomas