[manaox2]

Sorry to get into this, but found it interesting again suddenly. Is there a way to optimize buffer size or some other means to find out what latency settings are best if using a PC?

 

[Dan Lavry]

Quote:

Originally Posted by tosehee /img/forum/go_quote.gif Dan. Did you or someone say that most modern DACs are already equipped with some sort of reclocking chip which cleans the jitter? If this is true, then most if not all of new SPDIF converters are just plain marketing, or is it? I am curious because I do not want the placebo affecting my buying decision. As also, thanks for your thoughtful response and insight. With kind regards

I did not say that. But virtually all DA's have some jitter cleaning circuitry. At the minimum one has some circuit called a PLL (phase lock loop) which cleans up much of the higher frequency jitter content. There are other schemes as well, some are very sophisticated.

And jitter is not only about the timing errors in the signal arriving on some cable into the DA. Much of the jitter issue has to do with timing errors due to power supply, component and circuit noise, electromagnetic pick up, poor layout... All that is INSIDE the DA, and that is where most of the issues are.


I am not saying that one should ignore jitter on the data arriving to the DA on a cable, but that is often a very secondary issue.


DA jitter matters at ONE LOCATION - where the digital signal is altered to analog. If you have 10 nano second of jitter, arriving on a cable from and interface, but the jitter energy is at say ABOVE 5KHz, that signal may go through a PLL circuit before it gets to the DA (where it matters). The PLL may clean the jitter it up by say 40dB (that is very realistic) and if so, the jitter is attenuated from 10nsec to 100psec. (40dB is 100 time attenuation). So one guy is measuring 10nsec, the other guy does not hear the impact, because the DA circuit "fixed the problem". it Is that surprising?

It is no wonder that while one is measuring over 10nsec, another is not hearing it. If that jitter energy were at say 100 or 500Hz, the PLL would be of little help. It may not reject low frequencies at all. One needs to know more detail then just one number. A 20nsec jitter at 10KHz may be less of a problem then a 1nsec jitter at 500Hz. One needs to have much more detail then some "simplified overall number".


On top of what I said above, there are all sorts of jitter types, and some are very offensive, others are less offensive. A totally random jitter that is equally spread accross the frequency range tend to do least harm, probably just increase the noise floor by some amount. Jitter that is originated by the data (digital content) itself may have it's own character (change in timbre - coloration). Jitter that has a distinct frequency (such as line frequency, or some other coherent source) tends to make "tones at frequencies not related to the music" and that does not sound good...

It is important to know WHERE the jitter needs to be low, and that depends on SPECIFIC designs. A DA has more then one clock, often 3 clocks, and one has to know where jitter matters, and where it does not.

Looking at data transfer jitter, on the outside of the DA chassis, even at the end of a cable leading to a DA, is not a bad practice. Looking at the voltage, power, noise and so on is also good. But jitter on the outside can be 100 times higher then the jitter that matters, at the critical location inside the DA.


This is a rather complex subject. There is substitute for much learning and years of hands on in a well equipped lab, and I can not "clear the fog" in a few posts. But it is not surprising to me to see so many conflicting opinions.


Regards
Dan Lavry
Lavry Engineering

 

[Andrew_WOT]

Quote:

Originally Posted by Dan Lavry /img/forum/go_quote.gif I do not see the connection between jitter and software oversampling at the player.

Sorry Dan, you mentioned that higher bitrate makes jitter more pronounced, so I figured that upsampling in the computer could make converter or DAC work on jitter rejection harder.

 

[audioengr]

Dan Lavry wrote:

Quote:

It started out as some BS about minimum length of cables, and now we have a new nonsense. There is real technical knowhow based on real physics, and then there is all that made up nonsense. You will not find any credible literature or any real professional designer that takes such nonsense seriously. A designer needs to rely on real facts, and designing to the tune of such nonsense is going to lead to gear that does not work.

Cable length is a critical piece of the Transmission-Line formula. I do take it very seriously. Here is a white-paper with the engineering analysis:

spdif

These results were verified with double-blind listening tests by UHF magazine in Canada. They were skeptical about my white-paper at first, so they performed independent tests themselves. The editor of UHF brought the results issue of his magazine to me at CES several years ago, now a strong believer.

Steve N.
Empirical Audio

 

[audioengr]

Dan Lavry wrote:

Quote:

Why would you want to have a separate USB to spdif?

Simple. If a customer already has a great DAC but with no USB input, this adds the computer interface.

Quote:

The DA11 offers more features, such as the PIC (playback input control) allowing adjusting the stereo image width, as well as XLR outputs in balanced or unbalanced configuration (user settable), and a headphone output. It has a precision digitally controlled ANALOG volume setting (in 1dB steps), it is remote control reay (for universal remote controls) and much more. The unit is very robust, and the package is small.

Careful. There are rules here against advertising. I dont believe the poster asked about all of this stuff...

 

[Dan Lavry]

Quote:

Originally Posted by Andrew_WOT /img/forum/go_quote.gif Sorry Dan, you mentioned that higher bitrate makes jitter more pronounced, so I figured that upsampling in the computer could make converter or DAC work on jitter rejection harder.

Where did I say that higher bit rate makes jitter more pronounced? Can you point it out?

Regards
Dan Lavry

 

[nick_charles]

Quote:

Originally Posted by audioengr /img/forum/go_quote.gif Dan Lavry wrote: Cable length is a critical piece of the Transmission-Line formula. I do take it very seriously. Here is a white-paper with the engineering analysis: spdif These results were verified with double-blind listening tests by VHF magazine in Canada. They were skeptical about my white-paper at first, so they performed independent tests themselves. The editor of VHF brought the results issue of his magazine to me at CES several years ago, now a strong believer. Steve N. Empirical Audio

Do you mean CQ VHF ? - do you happen to know the Volume/Issue, some back issues are online.

 

[Dan Lavry]

Quote:

Originally Posted by audioengr /img/forum/go_quote.gif Dan Lavry wrote: Simple. If a customer already has a great DAC but with no USB input, this adds the computer interface.

I understand. Indeed people with a DA and no computer connection can use a good interface.

Regards
Dan Lavry

 

[Andrew_WOT]

Quote:

Originally Posted by Dan Lavry /img/forum/go_quote.gif And BTW, the real difficulties are much more pronounced at say 20 bit performance where the jitter requirement is 16 times tighter then at 16 bits! As a rule, the signal getting to the DA has much higher jitter than the jitter at the critical circuitry, and the DA clocking circuitry needs to clean it up.

Right here /\, may be I misinterpreted what you were trying to say.

Quote:

Originally Posted by Dan Lavry /img/forum/go_quote.gif Where did I say that higher bit rate makes jitter more pronounced? Can you point it out?

 

[Dan Lavry]

Quote:

Originally Posted by Andrew_WOT /img/forum/go_quote.gif Right here /\, may be I misinterpreted what you were trying to say.

Yes, Bits such as 16 bit word, or 20 bit word. That is the number of bits per sample. So in say a stereo digital audio there are a lot of bits - 16 to 24 bits for the left channel, and the same for the right channel, that already adds to up to 48 bits. In fact we have more bits reserved for various purposes and you and up with 64 bits for a sample pair.

Bit rate is the "speed" at which you send all that data. The data going on a single cable has to be all lined up in series, one bit after the other. So for 44.1KHz stereo data you automatically need to transmit 44100 X 64 = 2.8224MHz. In fact the rate is double that (for some good reasons!) so a 44.1KHz stereo ends at 5.6448MHz or around 5.6 million bits per second.

"Bit Rate" is about the the number of bits per second.

Regards
Dan Lavry

 

[tosehee]

I am sorry, but for noob like me, I can't seem to make up from the context. So, Dan. Are you saying that resampling in PC/Mac is generally bad or ?

Also, on the other response where you described the jitter, I re-read several times, but I do not know whether you answered my question or not. I think you did, but i just can't pick up from all those technical items. So, am I correct in saying that SPDIF converters and such that supposed to fight the jitters from PC to DA is useless since most of the DA already does some form of reclocking and the jitter where it matters the most is usually inside the circuitry?

Is this about right or ? Sorry again for not understanding your well thorough and informative response.

With kind regards

 

[Ektalog]

1. Andrew -- I perceived the same thing from reading Dan's statements over the last few days. I am glad you brought it up because Dan can then clarify. We may have read things out of context.

2. My take so far on the overall mis-topic ...even if he were proven "wrong", Dan is giving us the best perspective with no commercial vested interest. I cannot shake the feeling that Empirical's view smells funny due to the simple fact that they have more of a commercial involvement (not the same as commercial motivation). They still could be right...thus...

3. If you folks direct me to "cheap" 75ohm "same brand" cables of 2 lengths that will possibly show this effect, I will put them in my cheap

setup and attempt to find out for myself. All other things being equal...

4. My cheap setup IS so very so:

- From cPlay FLACs & WAVs via computer to
- Musiland USB 01 US (on its way from China)
- or E-mu 0404 USB
- Into old Denon 3805
- to Magnepan MMGs speakers (modded)
- or Sennheiser HD 280 pro (if returned by friend)

Kills 2 birds with one shot --- getting back to topic not the least of them!

Now back to my chair

 

[gevorg]

Quote:

Originally Posted by Dan Lavry /img/forum/go_quote.gif I did not say that. But virtually all DA's have some jitter cleaning circuitry. At the minimum one has some circuit called a PLL (phase lock loop) which cleans up much of the higher frequency jitter content. There are other schemes as well, some are very sophisticated. And jitter is not only about the timing errors in the signal arriving on some cable into the DA. Much of the jitter issue has to do with timing errors due to power supply, component and circuit noise, electromagnetic pick up, poor layout... All that is INSIDE the DA, and that is where most of the issues are. I am not saying that one should ignore jitter on the data arriving to the DA on a cable, but that is often a very secondary issue. DA jitter matters at ONE LOCATION - where the digital signal is altered to analog. If you have 10 nano second of jitter, arriving on a cable from and interface, but the jitter energy is at say ABOVE 5KHz, that signal may go through a PLL circuit before it gets to the DA (where it matters). The PLL may clean the jitter it up by say 40dB (that is very realistic) and if so, the jitter is attenuated from 10nsec to 100psec. (40dB is 100 time attenuation). So one guy is measuring 10nsec, the other guy does not hear the impact, because the DA circuit "fixed the problem". it Is that surprising? It is no wonder that while one is measuring over 10nsec, another is not hearing it. If that jitter energy were at say 100 or 500Hz, the PLL would be of little help. It may not reject low frequencies at all. One needs to know more detail then just one number. A 20nsec jitter at 10KHz may be less of a problem then a 1nsec jitter at 500Hz. One needs to have much more detail then some "simplified overall number". ...

Dan, does this mean that there is no such thing as "software jitter"? In other words, can different operating systems (Windows and Mac) or playback software (Winamp, Foobar, J.River, etc) have different effect on jitter? Assuming, in all cases that the digital output is set to bit-perfect (no digital volume, EQ, DSP, etc) and you're using the same device to output digital out.

 

[tosehee]

Get 2m from BJC. Quite cheap and they are true 75ohm.

 

[Andrew_WOT]

BJC is a good recommendation, also check e-bay for Zu Cable promotions, they make terrific cables. I use their Ash BNC http://www.zucable.com/cables/digita...&category_id=9