To Reclock or Not to Reclock ...

[SteveChicago]

I'm a fan, not an expert, and I need some advice please.

 

I have a modded Esoteric D70 DAC, which I like very much. However, to take advantage of its dual word clock capability I would need to purchase something like the Weiss AFI1 interface. An alternative would be to use a reclocker, like the Empirical PaceCar. Another alternative would be to swap this DAC for another that combines the two, such as a Weiss 202 or Antelope Zodiac+.

 

I currently have a modestly priced FireWire interface acting as a master clock via S/PDIF to the DAC. The sound is very good IMO but (of course) I'm interested in improvement.

 

My first question is what's actually going on: Is the DAC's clock being completely bypassed with my current configuration?

 

Next: Would replacing the current interface with a quality reclocker improve the sound?

 

Third: Has anyone compared these alternatives and, if so, what are your thoughts?

 

Thanks very much,

 

Steve

 

[jesk]

Only a DAC with a clock will give you a nearly perfect sound. Everything else is just marketing. Its like copying the sound file to the DAC and read + play it there.

 

[The Computer Audiophile]

Hi Jesk - Can you provide more info on why you believe what you do about this topic?

 

[SteveChicago]

My DAC has an internal clock. Sorry, but I don't understand your comment.

My question, among others, as stated above is whether its clock is engaged in the current set up.

 

[SteveChicago]

Hi Chris,

 

I'd certainly value your input on these questions (assuming I've presented them in an understandable way)

 

Steve

 

[audioengr]

A DAC with an internal clock has both advantages and disadvantages.

 

Advantages:

 

1) if you can control the streaming frequency of the source, then this is a most ideal situation

 

Disadvantages:

 

2) most sources cannot be controlled (no word-clock input)

3) you have no idea what the quality of the master clock inside the DAC is - could be terrible. Big brand names are no guarantee

4) If the internal DAC clock is controllable, then it is some kind of VCO or PLL. This will have higher jitter by definition

 

IMO, you are probably better off to use a better external converter with master clock and drive low-jitter AES or S/PDIF to the DAC.

 

Steve N.

 

[Mr.C]

There was a comparison on this board with the AFI1 and the Pacecar. I think the Pacecar edged the AFI1, but I'm not sure if the Zodiac or 202 were compared at all.

 

[vortecjr]

I was running some tests with a DVD-Audio player via spdif output into my L22 audio card and analog output from the card to my processor. This was sounding pretty great and I was wondering why as the computer usually sounds better:) I entered some commands and found one that would make it sound bad again:) I called Lynx and they advised that my initial pass through was being reclocked by the L22 card and the subsequent command would turn off the reclocking feature. WOW what a difference the reclock makes!

 

Jesus R

www.sonore.us

 

[SteveChicago]

Thanks Steve,

 

FYI and FWIW, the manual on the Esoteric D70 states, in pertinent part:

 

"In the D70, a servo-free direct clocking system is used, which comes close to the ideal of control. In systems where a clock other than the one derived from the digital audio signal is used, typically PLL technology is used to keep the clock frequency as constant as possible.

* * * The new method employed in the D70 to maximize audio quality is to use a DAC locked to a direct crystal-controlled fixed-frequency clock. This allows the conversion to be carried out independently from the input frequency and input jitter is therefore eliminated. In the case of non-synchronization, the RAM Link buffer eliminates any potential problems."

 

Does this affect your analysis?

 

Steve

 

 

 

[jesk]

Imagine the following:

 

You have a audio source in 44.1Khz/16bit. Its digitally modulated in PCM. Now it gets read. Its pulse modulated to your transfer-media. Let it be Ethernet, USB, SPDIF, whatever, it doesn't matter. To get that stream modulated over the cable/fibre it needs to went through the multiplexing units on the interfaces. Then multiplexed on the cable. Demultiplexed again. Demodulated. And then fed directly without any further digital processing to the DAC. Means: 44.100 ticks per second 16 bit big data segments. Segment for segment it needs to be as accurate as 0.00002267573696 second. No segment has to arrive faster or slower than after 0.00002267573696 second. If it would the sound couldnt be reconstruected as it was.

 

Now there are resampling DACs which use a not-100% accurate rate and resample it to a accurate one. What has to be done for this? Sure it has to buffer. Wait. Wait. Wait. Calculating the rate and finding it out of the average rate of the receiving data stream. Now it has enough and can stream this data clocked as precise as possible with a local clock to the final converting DAC chip.

 

There is no other good way to do this and there isnt a need to do it another way. Compare it with copying a audio file over USB to some devices flash which then reads and plays it. No real difference. If cables are crappy, SPDIF, USB, Ethernet hasnt any auto correction on its physics. This has to be done on some higher layers like in TCP or in an application itself. So if data-loss is happening the receiver cant handle that. The DAC will in this case just convert whats there and sound quality decrease will happen. But dont be afraid. Under normal circumstances there is no loss. Period again. So no need for some retransmiting upper-layers. Upper-layers with retransmitting functionality like TCP will just introduce jitter. Jitter is in audio a no-go. Like in VoIP audio should arrive fast and without much latency. Retransmitting is worse. As data-loss is only happening in broken setups nobody has to deal with that and like in RTP data is sent without acknowledgements on the receiver site. USB and SPDIF/AES is the same. No acking.

 

So under that definitions why the hell should one want to rely on the precission on arriving audio/data ticks? This isnt accurate and wouldnt work good without a buffer mechanism. Even el-cheapo VoIP hardphones have buffer to buffer voice first before playing. This is a must, because nobody can guarantee exactly arriving audio data.

This cant be guaranteed in Ethernet nor in USB nor in SPDIF nor anywhere. Nothing is 100% accurate. Especially not on systems with many elect-ric/ronical units and *cables*.

 

So discussions about asynchronous USB (which is nothing more than a layer which controls and guarantees the data like in TCP) is totally nonsense. Because its not needed. The receiver has even in that case to buff for the best and to clock again.

 

So to get to your question: Sorry, but I dont know your hardware, what it does and what not. Normally I first buy something which I do know and know what it does and what it does not. But maybe its possible for you, maybe with my/our help, to understand your setup more and answer it for yourself.

 

cheers,

 

Christian Meutes

---

I'am a networker, to me data is just protocol overhead

[email protected] - [email protected] - JESK-RIPE

 

[SteveChicago]

Thank you Christian for trying to sort this out. I'm not sure I follow you (and no doubt that's my lack of expertise, rather than your explanation). What I glean from your comment is an opinion that an external clock is neither necessary nor beneficial because my DAC has a RAM buffer that should resolve problems that might result from jitter. Do I follow you?

 

Steve

 

[jesk]

No and yes.

 

An external DAC has a clock or should have at least and it should have Jitter-Buffer.

 

 

 

 

 

Christian Meutes

---

I'am a networker, to me data is just protocol overhead

[email protected] - [email protected] - JESK-RIPE

 

[SteveChicago]

Again, my DAC has both an internal clock and a RAM buffer (128 MB).

 

Here's a link to information on this DAC

 

http://esoteric.teac.com/dacs/d-70

 

I'm not sure anyone's answered the following question in my OP.

 

1. With the FW interface I'm now using is the DAC's internal clock being utilized or bypassed?

 

Steve

 

 

 

[jesk]

I don't know. Knowing that means having information from your DACs vendor which state that. But to be honest if it wouldnt use a clock it would sound crappy.

 

[The Computer Audiophile]

Christian - You speak in very absolute terms about only one way to do things. In my experience people who speak this way do not understand the other methods of doing things. Some incredibly brilliant audio engineers who've been doing this for decades would disagree with you on much of what your saying. If there was only one way to do things, everyone would do it that way.

 

The following statements really make me question all of your comments related to digital audio.

 

"There is no other good way to do this and there isnt a need to do it another way."

 

"So discussions about asynchronous USB (which is nothing more than a layer which controls and guarantees the data like in TCP) is totally nonsense."

 

It appears you ar a very smart person when it comes to some purely data driven communications within computer based networks. Digital audio is a completely different animal.

 

 

 

[SteveChicago]

Big Deal!

 

In the meantime NO ONE has answered my question:

 

1. Is the internal clock in my DAC doing anything at all or is it being bypassed by the interface which, by necessity (because it lacks word clock I/O), is the master clock?

 

2. If the answer is that the DAC's clock is now dormant, should I care and if so, what might be an improvement.

 

Steve

 

[audioengr]

Certainly it is a good thing to have a free-running clock. The question is whether they paid more than $1 for it and is the power supply powering it worth a damn. I would bet no on both.

 

Steve N.

Empirical Audio

 

[audioengr]

Jesus - there is no reason why computer-driven audio should not sound better than the best CD player or Transport. This is what we claim. Its even on our brochure for RMAF this year.

 

BTW, several of our customers reclock the Lynx with our Pace-Car.

 

Steve N.

Empirical Audio

 

[audioengr]

1. Is the internal clock in my DAC doing anything at all or is it being bypassed by the interface which, by necessity (because it lacks word clock I/O), is the master clock?

 

It has to be bypassed if it is not resampling. Only if the internal clock is selected will it be used, and you MUST synchronize the source to this using word-clock.

 

2. If the answer is that the DAC's clock is now dormant, should I care and if so, what might be an improvement.

 

If the DACs clock is bypassed, which it should be if you are using a standard transport or converter without word-clock input, then the incoming jitter is critical. This is the case with any DAC, even upsamplers that asynchronously reclock.

 

I would be surprised if you did not hear an obvious improvement when driving it with a low-jitter source and a good quality S/PDIF or AES cable (not Belden 1694A).

 

Steve N.

Empirical Audio

 

 

[SteveChicago]

That wasn't so difficult, now was it?

 

 

 

[vortecjr]

In my test the dvd-audio player was getting help from the audio card and the only reason it was sounded pretty good compared to the computer.

 

I prefer to send the clock from the dac so the dac is the master. Additionally, we did some tests with batteries and a linear supply and the card's clock is fine and let me tell you a simple battery powering the computer will take your breath away.

 

I don't see the point of reclocking the card with your unit when your customers can just use the usb input!

 

Jesus R

www.sonore.us

 

[barrows]

we must be careful about making absolute statements about different approaches to doing things.

 

"Jesus - there is no reason why computer-driven audio should not sound better than the best CD player or Transport. This is what we claim. Its even on our brochure for RMAF this year."

 

The above statement might be mostly correct, but consider the PS Audio PerfectWave Transport-there is absolutely no technical reason any computer based system should outperform it. Essentially, the PWT is a purpose built, computer system, but it is a transport.

 

Statements like this, while generally well meaning, can occasionally upset consumers, who sometimes know better.

 

Jesus: truly asychronous re-clockers have their place, as some folks have SPDIF input DACs which they love, and are not ready to replace. A well implemented, asynchronous reclocker, like Empirical's Pace Car, or PS Audio's forthcoming PerfectWave Lens, will output a low jitter SPDIF (or I2S) feed to a DAC regardless of the incoming jitter level. Of course, ultimately you are right though, the best choice will be a DAC with a built in asynchronous interface.

 

[jesk]

Chris, the whole thing about this story is money.

 

[jesk]

Jesus R, the DAC sends the clock? Sorry but do you understand the basic digital concept at all?

 

[jesk]

Barrows, asynchronous means "having controlled connection between two ends" and dont rely on "send and forget". Asynchronous in the case of digital audio is nonsense. Period.