Optical TOSLINK vs. USB: Which connection is better to connect a DAC?

[00940]

 
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USB is universal, doesn't really change from system to system.  Toslink is ruled by implementation on PC end, and DAC end.  Different receivers, jitter rejection, ect ect ect.

USB is not so universal. A USB DAC can implement two very different protocols (asynchronous or isochronous) and even two DAC using the same protocol can use receivers with very different performances. On the computer side, the quality of the USB signal can vary widely from a computer to another: some have very noisy ground lines, some have poor clocks, some don't have enough power and the USB connection suffer, and so on, and so on.
 
 
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I agree that there are pros and cons to USB and toslink-spdif when compared against each other. But coaxial-spdif is superior to both.

 
There's no way to make such wide ranging statement, it's all a matter of implementation. In theory, USB in asynchronous mode +isolation would be much closer to technical perfection than coaxial spdif.

 

[vert]

Yeah, I think buying a DAC with a good USB implementation, like the M2Tech Evo, which I believe has the hiface module, would save money with not having to invest in a USB converter. I have experience with not so ideal DAC USB implementations, and the sound quality isn't that great.

 

[grokit]

 
Quote:

Originally Posted by grokit 

I agree that there are pros and cons to USB and toslink-spdif when compared against each other. But coaxial-spdif is superior to both.

 


Quote:

There's no way to make such wide ranging statement, it's all a matter of implementation. In theory, USB in asynchronous mode +isolation would be much closer to technical perfection than coaxial spdif.

 

I agree with you as far as USB's potential, but my experience in reality is where I am coming from. I have tried all three types of USB audio (synchronous, adaptive, and asynchronous) as well as coax and optical, these are my impressions, and I stand by them. I recognize there is much more out there than what I have experience with, but I try not to state opinions about gear or tech that I have not listened to personally.
 
Also don't forget that these technologies are frequently combined, like when manufacturers add an asynchronous sample rate converter to an adaptive USB implementation, or use an adaptive USB chip that converts directly to S/PDIF inside the DAC. S/PDIF has been refined for many years in countless audio products, and this conversion technique can be a fairly good compromise between a simplistic adaptive implementation like the PCM270x chip from TI and a well done yet quite expensive asynchronous DAC design. There are inexpensive asynchronous DACs, but they usually require special software drivers which can bring about a whole new level of compromise.
 
Please take a look at my signature for the appropriate qualifiers (IMO, IME, YMMV, etc.), they apply to everything I post and if you put my statement into that context, you will see that it's not so wide-ranging after all.

 

[00940]

@Grokit: I know all that. The DAC I designed is using a pcm2707 followed by src4192. See my earlier posts in this thread for the rationale in picking those ICs and some links with interesting and somehow unexpected measurements.
 
 
PS: I disabled signatures a long, long time ago. Not knowing what your experience is, not knowing what your opinion is based on, it's hard to say what I should make of your initial statement then.

 

[grokit]

 
Quote:

@Grokit: I know all that. The DAC I designed is using a pcm2707 followed by src4192. See my earlier posts in this thread for the rationale in picking those ICs and some links with interesting and somehow unexpected measurements.
 
 
PS: I disabled signatures a long, long time ago. Not knowing what your experience is, not knowing what your opinion is based on, it's hard to say what I should make of your initial statement then.

I C. Lol that you disabled other's signatures, yet you present your own. I love the Latin quotes btw, my current favorite is "Quis custodiet ipsos custodes?"

 

[00940]

That signature must be 4 or 5 years old now... I disabled the signatures when the forum had layout problems and never went around the matter again. It's now fixed

 

[Drake22]

lol, so much BS in this thread.
 
It's not an analog signal, so it doesn't have frequency response. It's digital, 1 or 0, and it doesn't matter how it's carried. 
Noise? It's digital, there's no noise. The voltage usually used is either 2 or 5 volts. It's gotta be some hell of a distortion to turn 0 into 1, lol.
Jitter? That is just latency and it doesn't have any effect on the character of the sound.
 
There is no difference in sound between usb, optical, coaxial or hdmi. It's ridiculous to state otherwise.
 

 

[scootermafia]

Digital signals can be corrupted, despite being 1s and 0s.  There's all sorts of info here on head-fi if you know where to look.  Timing is important, too.  

 

[Prog Rock Man]

There is a lot of suggestion of differences, but no proof any such is audible, apart from out and corruption of the signal, which is obvious.
 
There is little to no evidence that jitter is audible except in extremes. In any case, jitter has nothing to do with the cable, except length which can corrupt the signal, which as above will be obvious.
 
 

 

[mikemalter]

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lol, so much BS in this thread.
 
It's not an analog signal, so it doesn't have frequency response. It's digital, 1 or 0, and it doesn't matter how it's carried. 
Noise? It's digital, there's no noise. The voltage usually used is either 2 or 5 volts. It's gotta be some hell of a distortion to turn 0 into 1, lol.
Jitter? That is just latency and it doesn't have any effect on the character of the sound.
 
There is no difference in sound between usb, optical, coaxial or hdmi. It's ridiculous to state otherwise.
 

 
The issue is not so much in the 1 and 0 world.  It's the part before and after that.  Remember that all of this is happening in real time.  There is the conversion of the mechanical process of reading and interperting pits and then converting that information to a signal. Then the signal hits the wire and then it gets recieved and then converted.  So really a lot of this process is analog in nature.  Yes, in code it is all 1's and 0's, but there is a lot of non 1 and 0 stuff going on underneith the covers to get it there.
 
I understand your perspective regarding differences in sound between different digital connections.  From my perspective, I have heard the difference clearly.
 
 

 

[grokit]

 
Quote:

lol, so much BS in this thread.
 
It's not an analog signal, so it doesn't have frequency response. It's digital, 1 or 0, and it doesn't matter how it's carried. 
Noise? It's digital, there's no noise. The voltage usually used is either 2 or 5 volts. It's gotta be some hell of a distortion to turn 0 into 1, lol.
Jitter? That is just latency and it doesn't have any effect on the character of the sound.
 
There is no difference in sound between usb, optical, coaxial or hdmi. It's ridiculous to state otherwise.
 

Read and learn:
 
http://en.wikipedia.org/wiki/Latency_%28audio%29
 
http://en.wikipedia.org/wiki/Digital-to-analog_converter#Practical_operation

 

[Drake22]

 
Quote:

 

Read and learn:
 
http://en.wikipedia.org/wiki/Latency_%28audio%29
 
http://en.wikipedia.org/wiki/Digital-to-analog_converter#Practical_operation

lol, 5k posts you have, are they all worthless like this?
 
What about latency? It's just a delay, the sound itself doesn't change.
What does this have to do with DAC when we are talking about cables, and how the data is carried INTO the dacs
 

Quote:

 
I understand your perspective regarding differences in sound between different digital connections.  From my perspective, I have heard the difference clearly.
 
 

Seriously? ... If there are no corrupted cables or ports, and everything is connected correctly, there can't be any difference... Because it's just data that is carried into the dac, in where it get's converted into analog.
DAC itself doesn't care in which way he receives the data. it's digital and that's it. No noise, no losses in digital transmission, so cable used doesn't matter. The only thing different between cables is the latency which just means you ll receive the signal sooner or later, but that doesn't change the sound itself.

 

 

[00940]

A little knowledge is a dangerous thing.
 
The DAC do care in which way he receives the data. In SPDIF (and in most USB protocols), the receiver chip recovers the system clock for the DAC from the timing of the incoming digital signal, through a PLL (a highly analog process). There is no dedicated clock line. The accuracy of this recovery affects the D/A process. That's where jitter enters the figure. Jitter is not delay, jitter is variation from the ideal timing. Some jitter can be traced back to the sending clock, some can be linked to the transfer interface (which is very much an analog thing). How much jitter is audible, that is debatable. However, the fact that jitter in spdif system can and do distort the analog output signal is well established. Some reading :
 
http://www.scalatech.co.uk/papers/aes93.pdf
http://www.wolfsonmicro.com/documents/uploads/misc/en/Jitter_performance_of_spdif_digital_interface_transceivers.pdf
 
I think you misunderstand the point about noise too. By linking the ground of the computer and the ground of the device, noise can couple through (of course it depends a lot on how your DAC is designed and layed out and this is especially true for non isolated, usb powered devices). It doesn't affect the "transfer of the data". It can however affect the proper operation of the chips inside your dac and reduce their performances. Spdif receivers and DAC are mixed-signal ICs, they rely on a very clean supply and ground to fully meet their specifications. That's why most datasheets include suggested layouts and the like.

 

[Drake22]

Quote:

A little knowledge is a dangerous thing.
 
The DAC do care in which way he receives the data. In SPDIF (and in most USB protocols), the receiver chip recovers the system clock for the DAC from the timing of the incoming digital signal, through a PLL (a highly analog process). There is no dedicated clock line. The accuracy of this recovery affects the D/A process. That's where jitter enters the figure. Jitter is not delay, jitter is variation from the ideal timing. Some jitter can be traced back to the sending clock, some can be linked to the transfer interface (which is very much an analog thing). How much jitter is audible, that is debatable. However, the fact that jitter in spdif system can and do distort the analog output signal is well established. Some reading :
 
http://www.scalatech.co.uk/papers/aes93.pdf
http://www.wolfsonmicro.com/documents/uploads/misc/en/Jitter_performance_of_spdif_digital_interface_transceivers.pdf
 
I think you misunderstand the point about noise too. By linking the ground of the computer and the ground of the device, noise can couple through (of course it depends a lot on how your DAC is designed and layed out and this is especially true for non isolated, usb powered devices). It doesn't affect the "transfer of the data". It can however affect the proper operation of the chips inside your dac and reduce their performances. Spdif receivers and DAC are mixed-signal ICs, they rely on a very clean supply and ground to fully meet their specifications. That's why most datasheets include suggested layouts and the like.

Okay.
About jitter. So are you implying that if I send a same digital sinewave, one through spdif, and one through coaxial, I will get different analog output? No I won't. It will be same analog output, hence the sound will also be the same. It's gotta be an insane jitter to corrupt the signal. Perhaps usb 1.0 or 1.1 dac could cause it but that is obsolete anyway. If you receive different analog outputs from coax and spdif that would just mean that the DAC is defective.
 
Again noise. No effect on the sound you confirmed that, thank you. Performance? Your sata bus of your harddrive gets the same noise. What kind of noise it has to be to corrupt the data?
 

 

[00940]

Quote:

 
Okay.
About jitter. So are you implying that if I send a same digital sinewave, one through spdif, and one through coaxial, I will get different analog output? No I won't. It will be same analog output, hence the sound will also be the same. It's gotta be an insane jitter to corrupt the signal. Perhaps usb 1.0 or 1.1 dac could cause it but that is obsolete anyway. If you receive different analog outputs from coax and spdif that would just mean that the DAC is defective.
 
Again noise. No effect on the sound you confirmed that, thank you. Performance? Your sata bus of your harddrive gets the same noise. What kind of noise it has to be to corrupt the data?
 

 
- Coaxial is a particular methode of transmitting spdif, so is optical. What do you want to say exactly ?
 
- It is mathematically proven that jitter, as small as it is, will corrupt the analog signal. Did you even read the first paper I linked ? Jitter as low as 150ps can be reliably measured in practice by analysing the analog output of a DAC. The question is how much jitter (and of which type, signal correlated or not) is needed to have an audible effect. To get an accurate analog signal, you need the correct samples values at the DAC input AND those values must be fed at the correct timing.
 
 
- You realize that most USB DAC on the market are still using USB 1.1 receivers from TI, don't you ?
 
- Don't put words in my mouth. Noise will not corrupt data but it will surimpose itself on the output signal and corrupt the analog signal. Example: depending on which PC I connect my usb DAC to (desktop, laptop on batteries, etc), I can get the noise floor (at the analog output) varying by as much as 6dB. With sensitive headphones, that can get pretty audible.
 
- SATA has error correction and works only with purely digital devices. It doesn't care much about noise. However, you have to realize that USB receivers, SPDIF receivers and DAC are real time, mixed-signal devices. They are nothing like SATA. You put noise on the spdif receiver supply and the (analog) PLL performance is reduced which in turn reduce the accuracy of the system clock it's producing. You put noise on the DAC supply pins and you'll find part of it on the analog output. It's not a matter of corrupted data.
 
 
You could read those too:
http://www.tnt-audio.com/clinica/diginterf1_e.html
http://www.stereophile.com/reference/1093jitter