[regal]

I have read papers where asynchronous reclocking in a DAC actually adds jitter. So I don't buy the "this DAC is immune to jitter" line. With anything in the audio chain there is a good budget solution except a low jitter SDIF source. There are few recommendations. Most info on CDP's center on the analog outs not the digital ones.

I love the NOS DAC sound so I am stuck looking for a low jitter source, but I have been unable to much info. I keep hearing the Phillips DVP642? is great but I am not buying that a DVD player would have low jitter with their clock frequency and PLL just to get 44.1k.

I looked into the CDPROM transport unit but the only company selling kits anymore is in europe and the cost is high.

I have looked at upgrading a clock in a budget CDP, but again there is very little hard evidence that this actually reduces jitter.

I guess I am getting frustrated with the lack of info. Why hasn't someone taken jitter measurements and reported to the masses?

 

[Scrith]

Good question. I've asked repeatedly to see jitter information for different sources (mostly computer-based, like internal sound cards and external USB or Firewire sound devices), but information about how much jitter is actually out there is really lacking.

By the way, there is a DAC that deals with jitter in a unique way (without resampling): the Lavry DA10. See the Lavry website for a white paper that discusses his unique approach.

 

[Garbz]

It's not unique. It's simply a form of synchronous reclocking. However it also is not perfect. Modulating the clock to deal with differences between the clock and the incomming stream causes problems, but on the grand scale this is minor to the jitter it attenuates.

As far as sources go, what do you mean there's no hard evidence about reclocking? It all depends on which clocks you look at. Many clocks often replace just the primary oscillator. The problem is that jitter is induced by the ciruits that are connected to it.

This is especially useless on a DVD-player where the oscillator is usually a video frequency and not a multiple of an audio frequency. The approxmiated audio clock is then just that, approximated. However for a CD transport the situation is different.

If you can find a CDplayer who's primary clock runs at a frequency usable for S/PDIF, units such as the Tentlabs XO-3 will indeed dramatically reduce output jitter, although the XO-2 unit falls into the category mentioned above. If a very stable clock source is available then a simple $0.30 D-Type Flipflop can sync the S/PDIF data to this clock to produce an S/PDIF output with the jitter characteristics of the clock itself.

Also before someone posts links to "actual" jitter measurements I invite you to have a look at the process. One well known magazine *ahem* stereophile *ahem* have in several cases I have seen measured the jitter at the analogue outputs of the benchmark DAC1. The problem ofcourse is all the fancy reclocking and screwing with the I2S lines DACs do really means the results are no where near representitive of what goes in.

If anyone can find reviews of jitter performance that measures the jitter using a dedicated PLL or some other digital means please let me know.

 

[Scrith]

(sorry to derail, skip if you are only interested in the original question about jitter from CD-based transports)

Quote:

Originally Posted by Garbz It's not unique.

Is there another DAC that uses the approach Lavry does? One of the things that is interesting about his DAC is he lets you choose (via a switch on the front) how it deals with jitter: normal (a traditional approach, used in many older/simpler DACs), wide (upsampling, used by DACs like the Benchmark DAC1), or what he calls his CrystalLock method (which I haven't seen on another DAC, but then again I do not have complete knowledge of every DAC).

You say it isn't perfect, but, realistically, there is no "perfect" way to deal with jitter from S/PDIF, because the DAC has no control over the speed of the incoming data. Some would argue for clock synchronization between the DAC and transport, but that has the potential to add jitter as well (and, even if the clock signals could be transported instantaneously, who can be sure that the clock being replaced isn't at least as good as the one that is taking charge, or that the device that is now being run by an external clock can properly speed up or slow down to match it?).

Basically, there is no way to get rid of jitter with an external DAC that has no control over incoming data. But I think the Lavry comes as close (as I've heard, at least) as is currently possible to minimizing it. If you know of a DAC that can deal with jitter more effectively than a Lavry, please make this information public!

Whether or not you actually need a DAC that can reduce jitter as much (or more) than a Lavry (or a DAC1, for that matter) is open to conjecture. Can you actually hear this jitter that everyone is so concerned about? I don't know.

The ultimate solution (as discussed in other threads) appears to be to use an asynchronous protocol to move the data from the transport to the DAC at a speed controlled by the DAC. The DAC then buffers the data internally, sends it to the DAC chip from its own buffer using a local clock, and outputs it from the DAC chip based on the same local clock. Unfortunately, I don't think such a device exists yet. And the DIY guys (and the small companies that create devices like those made by the DIY guys) won't be the ones to make it, because it will require custom driver software to support this new asynchronous protocol. And then you have to wonder why a large company would think it is worthwhile, given that few people will bother to buy this ultimate asynchronous DAC for use with their computer (the only transport likely to be able to support it). So get used to jitter and try to use a DAC (and/or some other device along the way) that minimizes it!

 

[Garbz]

Quote:

Originally Posted by Scrith snip

You are very right. There is no ideal approach, and I was not saying anything negative about the DAC. Infact from what I've heard it is an excellent DAC. I am just saying that the technique is not unique. It is simply synchronous reclocking which is MUCH harder to design and impliment then Asyncronous sample rate conversion which is what many other DACs use to attenuate jitter, and in theory sync reclocking actually works properly too

As for the separate transmission of the clock, this can be done jitter free. A properly terminated coax cable will generate picoseconds of jitter. As for the clocks being standard there's a new problem. Ideally all DACs would REQUIRE an external clock, or would REQUIRE a cdplayer that could properly sync to it's clock. If the DAC has a good clock that is syncronous to the data being received then reclocking is easy. Trying to get technology like that in consumer gear, now that is the challenge.

 

[regal]

Quote:

Originally Posted by Garbz . If you can find a CDplayer who's primary clock runs at a frequency usable for S/PDIF, units such as the Tentlabs XO-3 will indeed dramatically reduce output jitter, although the XO-2 unit falls into the category mentioned above. If a very stable clock source is available then a simple $0.30 D-Type Flipflop can sync the S/PDIF data to this clock to produce an S/PDIF output with the jitter characteristics of the clock itself.

So what's a good candidate for the XO3 ?

 

[Garbz]

I can't get exact model numbers or brands for you but my guess is most if not all dedicated cdplayers inc hdcd players would be sufficient. So no SACD, DVD-Audio, DVD-Video or any other multiformat players. This may possibly extend to cd mp3 players as well. Furthermore the cdplayer should not resample the output to 48khz.

But you are after some device that uses a master clock with a frequency of 8.4672 11.2896, 16.9344, 22.5792 or 33.8688Mhz which are the 192 256 384 512 and 768 multiples of 44.1khz used on CDs. These are ideal. THe XO-3 will still work for other players but the reclocking circuit becomes somewhat less precise.

Try to find out this info beforehand, or get a gurantee from the place which is selling the device and return it if you find one that isn't right.

 

[adhoc]

Want a good (and cheap-ish) transport?

Buy any old CD player that used the CDM 4/19 or CDM 4/11 transport mechs, and tap I2S directly from the SAA72XX/73XX decoder chip. You *must* have SAA72XX/73XX decoder chips.

Alternatively, you could pick up a philips CD304 mkII, the only CDP to have had a (legendary) CDM1 married to a SAA7210 decoder chip. All the other CDM1 mechs had 14bit output decoders that did not speak I2S.

For both methods you could also strip the TDA1541s [a DAC] from the players for personal use or extra $$. Some players might even come with S1 or S2 - 'selected' grades of TDA1541.

The only drawback to this approach would be 1) lack of parts once the laser dies (and it eventually will) 2) same as #1.

 

[Mehow]

I have the Philips CD304 MKII for sale now, if anyone is interested. 

 

[thegunner100]

  I have the Philips CD304 MKII for sale now, if anyone is interested. 

... seriously?

 

[Mehow]

Yeah. No joke.
Perfect technical condition. Never modified or repaired.
Very good visual cond as well.
 

 

[Mehow]

I wanted to put it up on ebay and here, but I don't have enough posts count.
So now I'm jumpin around different subjects posting to be able to do that finally.
Have got other great gear for sale too. Everything well selected and loved.
Have to sell them for financial reasons.