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?
post #286 of 1712
11/20/09 at 9:25pm
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
|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.
|Why would you want to have a separate USB to spdif?|
|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.|
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.
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:
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.
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.
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".