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post #631 of 835

I think digger945 was testing your sarcasm radar. It failed.

post #632 of 835
Quote:
Originally Posted by chinesekiwi View Post

I think digger945 was testing your sarcasm radar. It failed.


I've heard the "I didn't want to like it, but I did!" argument against bias far too often to think of his as sarcasm.

post #633 of 835
 


Quote:
Originally Posted by chinesekiwi View Post

I think digger945 was testing your sarcasm radar. It failed.



Thank you.

 

post #634 of 835
Quote:
Originally Posted by digger945 View Post




Every single part of the system is the same right down to the song. The only change is the USB to SPDIF converter. This past June makes one year comparing.

 

 



That's still not very specific.  Are we talking hypothetically here or actual examples of what people are experiencing?


Whatever the case, my explanation would simply be that for some reason the amp outputs one of them at a higher volume than the other one.  This can make people feel that the "bass is fuller" and basically feel like everything sounds better.

post #635 of 835
Quote:
Originally Posted by DaBomb77766 View Post





That's still not very specific.  Are we talking hypothetically here or actual examples of what people are experiencing?


Whatever the case, my explanation would simply be that for some reason the amp outputs one of them at a higher volume than the other one.  This can make people feel that the "bass is fuller" and basically feel like everything sounds better.



 

My system. My amp. My usb to spdif transports. Stuff I have listened to for years now.

 

Balanced Dynahi.

0404usb. Gamma 2. Halide Bridge. 

Balanced Denon 2k. Grado 225. Senn HD250. Fostex T50RP.

 

  I guess I thought that somehow the act of controlling the usb controller from an external source might have some bearing on the whole conversation.

 

 

post #636 of 835

The evidence is certainly waited in favour of the argument that USB cables do not influence sound quality. There is only speculation as to how a USB cable could affect sound quality, which in a science forum is not good enough.

post #637 of 835

Well you can probe that a cable can affect the square waveform of a digital signal, and that this influences jitter, and that jitter can introduce distortion.

 

00940 appears to have a good understanding of the metrics in question, so I will refer to his previous post which will do much better than anything I can cobble up:

 

 

 

Quote:
Originally Posted by 00940 View Post

-1- Waveform distortion: due to its physical properties, the cable can possibly affect the square waves, in interaction with the source and receiver (from that point of view they form an analog system). This in turns affect the accuracy of the recovered system clock fed to the DAC chip. This in turns affects the accuracy of the digital to analog conversion.

-2- Interaction in between power supply lines and data lines: it has been measured that 1Khz spikes coming from the data lines can couple into the power supply lines and that the longer the cable, the stronger the effect. Such spikes could maybe be directly heard as noise depending on the dac's pcb layout. Such spikes could also affect the accuracy of the ICs inside the dac, resulting either in increased jitter (for the clock or the receiver chip) or directly in higher distortion (for the dac chip and the opamps of the analog section).

-3- Rfi shielding: the usb cables are quite susceptible to high frequency noise pick-up (a reason among others why long runs cannot be used). Noise making its way into data line can perturbate the receiver chip, causing early/late triggers, resulting once again in a poorer system clock. If the noise couples into the power supply lines, see -2-.

-4- HF noise attenuation: the source computer signal's quality can vary widely. HF noise can find its way on the various USB lines. A cable attenuating this HF noise could thus have an impact. It could however interacts with -1-.

 

All these are sound engineering reasons and have been measured or could be, given time and the proper (read expensive) equipment. The fact that USB cables affect the analog output of the DAC seems to have been proven by measurements by Paul Miller for the january issue of Hifi News (if anyone has the article, I'd love to read more than hearsay).

 

HOWEVER, the existence of a technical difference in between cables does NOT prove the existence of an audible difference. It is even more so as the differences outlined above are fairly small and that cables manufacturers don't seem to bother measuring the actual differences their cables make. And you have to keep in mind before any generalization that USB audio uses 3 different protocols with various levels of weakness to those problems, that the USB receiver chips are very different and that DACs are coming from a bazillion different manufacturers who pay more or less attention to their designs.

 

 

post #638 of 835

Very good quote. One thing to note is that all the things he mention are either skipping, or distortion / high frequency noise. Even at a stretch -- assuming that USB cable can reduce distortion, there's still no possible way it can effect the actual sound signature -- like boosting bass, for example.

post #639 of 835

 

Quote:
I will not insist that a USB cable cannot possible impact the analog signal ...

Good!  Progress!  smile.gif

 

Quote:
 ... but it will be practically impossible to measure the change

Yes, I almost agree with that.  When talking about jitter, it is not actually so hard to measure it, and quantify it.  What does represent a challenge, though, is to perform a rigorous analysis of the impact of jitter on a resultant analog waveform, and to thereby come up with a definite objective of something to look for and measure that is quantitatively representative of something that could be audible.  There are measurements you can make on an analog waveform, and things that you can look for in those measurements that can be shown to be artifacts of jitter, but I don't think anybody would claim to be able to tell you what these things should actually sound like.

 

DaBomb, can I solicit your views on audibility vs measurability?  Would you, for example, state that because a thing cannot be measured therefore it cannot be audible?  What about the other way around.  Would you state that anything that is audible can de facto be measured?  For example, I think we all would agree that some systems can project a much-prized "holographic soundstage".  I know of no way of measuring that property.  And I don't mean that we can't measure things that tend to correlate well with sound imaging.  Just that we can't actually measure a system's imaging in any quantitative way.  I am wondering, DaBomb, would you agree with that?

post #640 of 835
Quote:
Originally Posted by Talos View Post

 

DaBomb, can I solicit your views on audibility vs measurability?  Would you, for example, state that because a thing cannot be measured therefore it cannot be audible?  What about the other way around.  Would you state that anything that is audible can de facto be measured?  For example, I think we all would agree that some systems can project a much-prized "holographic soundstage".  I know of no way of measuring that property.  And I don't mean that we can't measure things that tend to correlate well with sound imaging.  Just that we can't actually measure a system's imaging in any quantitative way.  I am wondering, DaBomb, would you agree with that?


 

I would agree that we cannot measure a system's "imaging" in any real sense.  However, "imaging" is a very abstract term...and many people don't seem to understand what it means.  It's more to do with how your brain processes the information it receives.

 

Still, I do agree that somethings like that cannot be expressed in data...however, I don't think the case is that it simply cannot be measured.  It's just that we don't know how to interpret the data correctly.  I'm sure all of the data is there - everything we can hear, the microphones can hear better.  However, what we don't understand is exactly how the brain processes this information, and thus, we don't know what part of the signal equates to "holographic imaging."  Maybe some day when we have more accurate psychoacoustic models that are derived from actual studies of how the brain processes audio information this will change...but we just don't know yet.

 

As such, my view is, whether we understand what the change is or not, our current equipment can measure everything that a cable change could possible affect.  Maybe the tiny little changes that we dismiss as "inaudible" actually make a difference - I don't know.  But the point is, no data whatsoever points towards a USB cable changing the signal in any way whatsoever.  If it does then maybe there will be something to this myth.  Until then, I simply have no choice but to dismiss it as your typical audiophile mumbo-jumbo.

post #641 of 835

Whenever a discussion degenerates to the point of discussing the "immeasurable" or un-interpretable data, it becomes a useless debate. Unless, you do a double blind test.

 

As for double blind tests: If USB cables had an audible difference, no matter how subtle, a trained expert "believer" whose listened to both extensively should be able to distinguish them blindly. And that's all I have to say for the double blind area.

 

Beyond that, lets try to stick to the scientific observations of USB cable: There is a remote possibility that a bad cable would introduce jitter (= high frequency distortion) into a retardedly designed (unbuffered) DAC, skipping, and maybe background white noise.

 

Ok, giving the "believers" the benefit of the doubt, I ask: Do you still assert that USB cables can give you a different sound signature? Like boosting bass, for example?

 

I think if we want this discussion to be productive we need to focus on the issue I highlight above first. Noise will always be a tiny little unmeasurable possibility, and jitter is possible with an unbuffered DAC. However if your DAC does run off a buffered source, and with its own local clock, then USB-dependent jitter simply should not be happening.


Edited by ac500 - 8/2/11 at 2:58pm
post #642 of 835

Originally Posted by ac500 View Post

 

giving the "believers" the benefit of the doubt, I ask: Do you still assert that USB cables can give you a different sound signature? Like boosting bass, for example?


of course not, more like a clearer sound/soundstage...as in less jitter/THD.

post #643 of 835

Ok, so it's mostly just a debate regarding jitter.

 

In this case, I wonder if anyone with a buffered DAC would comment. A DAC running off a buffered data source and an internal clock should have no USB-dependent jitter whatsoever.

post #644 of 835
Quote:
Originally Posted by ac500 View Post

Ok, so it's mostly just a debate regarding jitter.

 

In this case, I wonder if anyone with a buffered DAC would comment. A DAC running off a buffered data source and an internal clock should have no USB-dependent jitter whatsoever.


I don't know how the Benchmark DAC1 handles USB jitter specifically, but a graph in the manual shows that its jitter isn't affected by cables (probably coaxial) 1000 feet in length.

 

When it gets here I could do some subjective sighted comparisons between the uDAC and the DAC1, but that would hardly be a fair comparison in other aspects like general THD+N and crosstalk.  I won't be able to separate all of that out from the jitter. I don't exactly know what jitter is supposed to sound like.


Edited by Head Injury - 8/2/11 at 4:15pm
post #645 of 835

The Benchmark DAC1 sends all incoming digital signals (coax or usb) through an AD1896, an ASRC. This ASRC's output is clocked by a local low noise clock. As such, any jitter in the incoming signal is heavily reduced by the ASRC's filters and the little that cannot be suppressed transformed into noise. The reduction is good enough for this amount of noise to be very low, for any reasonable incoming amount of jitter.

 

As a matter of fact, according to this Stereophile's article quoting the designer of the DAC1 ( http://www.stereophile.com/digitalprocessors/108bench/ ), the implementation chosen by Benchmark for the TAS1020b (the chip converting USB signals to I2S) leads to "significant" amount of jitter. This jitter is however nicely reduced by the ASRC.

 

The only way I can imagine for an USB cable to significantly alter the jitter of the clock fed to the DAC1's AD1853 would be through noise coupling... the local oscillator jitter figures are indeed function of the quality of the power supply it's being fed. Good PCB layout practices would make this concern go away and we can safely assume that those practices were applied.

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