Head-Fi.org › Forums › Equipment Forums › Computer Audio › Sound quality difference: USB vs S/pdif optical digital output?
New Posts  All Forums:Forum Nav:

Sound quality difference: USB vs S/pdif optical digital output?

post #1 of 16
8/21/08 at 8:40pm
Thread Starter 
Hi I am going to buy the Benchmark DAC-1 within the next couple of weeks and was wondering if there is any difference in sound quality between connecting the DAC-1 (or any dac for that matter) to my macbook pro through the USB slot or from the macbooks S/pdif out to the dac-1's S/pdif in? I've looked around for reviews on the dac-1 usb but they never seem to point out what difference it makes whether it's USB or not...

Basically I don't want to be buying the DAC-1 USB for more if I can get exactly the same audio quality from the original cheaper DAC-1 as it seems to me they have the same componants and headphone amp.

Thanks
Reply
post #2 of 16
8/21/08 at 9:07pm
What exactly is it you searched for? Type in "USB SPDIF" in the search and you get this helpful thread: http://www.head-fi.org/forums/f46/us...d-card-347605/
Reply
post #3 of 16
8/22/08 at 1:45am
Thread Starter 

..

I looked looked around google and this forum to see if there was a sound quality difference between USB and spdif when connecting a DAC to a laptop (macbook). There are plenty of threads mixing both subjects but I haven't found one that answered my question yet.
Everyone seems to be insinuating that there is no audible difference between the two. If that was the case why Bring out a more expensive USB version when laptops already have a digital spdif out (headphones out) ?
could someone explain why anyone would opt for the USB version?
Sorry if the answer to this is really obvious, I'm still learning...
Reply
post #4 of 16
8/22/08 at 2:04am
It's simple - lots of equipment outputs S/PDIF like CD/DVD players, etc, but only computers output USB. Most DACs use USB to S/PDIF or USB to I2S converters and feed the converted digital signal (S/PDIF or I2S) to the DAC chip; that means that the USB input module is just an extra part to the same DAC unit which costs more money than the DAC without that module.

As for audible differences between the two, this isn't exactly as simple - it depends on the quality of the output of the source and input of the DAC.

1) The output signal has to be strong, bit-perfect, low noise, low-jitter and precisely clocked. If both S/PDIF and USB meet those requirements, they should be the same, but since there are very few (if any) "high quality" USB units on computers and lots of dedicated sound-cards that are meant to output as close to perfect S/PDIF, it's more likely you'll get a better S/PDIF signal than USB. Both protocols are streamed and without any error correction so if the signal is off in timing or gets corrupted in any way, there is no way to change it, that is what the DAC will receive.

2) The input receivers must be of good quality, resistant to noise and be run off clean power supplies. Obviously quality here matters - if the USB receiver is REALLY good and the S/PDIF receiver is not, you'll have a better USB signal. How the DAC works also matters: if you have a DAC that runs off S/PDIF signal, than using USB is another link in the chain (USB-S/PDIF converter), so it is more likely you'll have a better signal off S/PDIF. If though the DAC is fed I2S in which case both S/PDIF and USB are converted to I2S, the quality of the receiver is the only thing that should make a difference.

Hope that helps, mostly background info, you make up your own mind as which route to take and hopefully research the DAC you're looking at to see how to best connect it.
Reply
post #5 of 16
8/22/08 at 2:18am
Thread Starter 
Thanks for the reply,
so basically it all depends on the quality of my computers USB or s/pdif output. I will be connecting the benchmark DAC-1 to my macbook pro, so judging by what you are saying There shouldn't really be any difference (the dac-1 is ment to be as close as possible to jitter free). For some reason i just can't imagine audio coming out of through a mini-jack s/pdif being as good a quality as USB. But hey, thats why I asked
Reply
post #6 of 16
8/22/08 at 1:53pm
Guess it all runs down to the implementation, and the quality of the units involved.
I have run my Isabellina with both USB and optical S/PDIF, and to be honest I could not hear a difference.
Reply
post #7 of 16
8/22/08 at 2:06pm
Generally it is a better idea to use USB to connect to a DAC1. With S/PDIF you are somewhat at the mercy of the audio chip/board that is outputting the S/PDIF signal (and there are some pretty awful audio chips/boards out there, which do bad things like resample all outgoing audio to 48K). With USB this shouldn't be a problem (basically the audio data will be sent directly to the audio device for it to deal with as it sees fit).

Yes, there are some audio chips/boards that will not mess with the audio data (or that will only mess with the data if the audio program you are using it set to use certain audio I/O protocols).

Yes, it is possible that you could have some software on the computer that will mess with the data before it is sent to the USB port.

But, generally, USB should be a safer choice, because it removes some totally unnecessary hardware (the audio chip/board) from the process. This audio hardware is usually designed for the purpose of creating analog audio outputs, not digital ones, so the quality of the S/PDIF output is sometimes questionable. The USB port hardware, on the other hand, is designed for extremely high speed data transfer (MUCH higher than is necessary for audio), so it should be up to the task of outputting a relatively small stream of data to your DAC.
Reply
post #8 of 16
8/22/08 at 2:14pm
The DAC-1 reclocks the stream, so jitter in the normal sense is a nonissue.

Really crappy hardware or drivers could still cause a problem, though.
Reply
post #9 of 16
8/22/08 at 3:01pm
Good question, I've been wondering this myself
Reply
post #10 of 16
8/22/08 at 4:12pm
Thread Starter 
So, does anyone know if a macbook pro's S/pdif output and soundcard that was bought new last january (just before the newest generation of macbooks) would be good as good as its USB input?
Reply
post #11 of 16
8/23/08 at 5:04pm
Thread Starter 
no one?
Reply
post #12 of 16
8/23/08 at 5:05pm
Thread Starter 
sorry I'm a little impatient as there a bid on dac 1 ends tomorrow and its going for quite cheap
Reply
post #13 of 16
8/23/08 at 6:12pm
Perhaps even more important to consider: there's actually some contention as to whether late model DAC-1s have better SQ then it's predecessors.

I can tell you that the USB implementation on the 2008 DAC-1 is excellent, and sound quality differences between optical and USB are negligible at best.

If you're getting a great deal on a late model DAC-1 (non usb) I would say go for it. This is especially true if you are confident you'll be sticking with Apple.
Reply
post #14 of 16
1/23/12 at 8:00pm



 

Quote:
Originally Posted by FallenAngel View Post

It's simple - lots of equipment outputs S/PDIF like CD/DVD players, etc, but only computers output USB. Most DACs use USB to S/PDIF or USB to I2S converters and feed the converted digital signal (S/PDIF or I2S) to the DAC chip; that means that the USB input module is just an extra part to the same DAC unit which costs more money than the DAC without that module.

As for audible differences between the two, this isn't exactly as simple - it depends on the quality of the output of the source and input of the DAC.

1) The output signal has to be strong, bit-perfect, low noise, low-jitter and precisely clocked. If both S/PDIF and USB meet those requirements, they should be the same, but since there are very few (if any) "high quality" USB units on computers and lots of dedicated sound-cards that are meant to output as close to perfect S/PDIF, it's more likely you'll get a better S/PDIF signal than USB. Both protocols are streamed and without any error correction so if the signal is off in timing or gets corrupted in any way, there is no way to change it, that is what the DAC will receive.

2) The input receivers must be of good quality, resistant to noise and be run off clean power supplies. Obviously quality here matters - if the USB receiver is REALLY good and the S/PDIF receiver is not, you'll have a better USB signal. How the DAC works also matters: if you have a DAC that runs off S/PDIF signal, than using USB is another link in the chain (USB-S/PDIF converter), so it is more likely you'll have a better signal off S/PDIF. If though the DAC is fed I2S in which case both S/PDIF and USB are converted to I2S, the quality of the receiver is the only thing that should make a difference.

Hope that helps, mostly background info, you make up your own mind as which route to take and hopefully research the DAC you're looking at to see how to best connect it.


Sorry for bumping an old thread, but is this still true? There are a lot of USB DACs on the market now, and I assume they have DAC chips that take USB input. Take the example of a recent DAC that has both S/PDIF and USB inputs - does one input get converted to the other, so that there's always 1 superior interface? Or do DAC chips now support multiple inputs?

 

Also, I've heard in some cases async USB has better jitter performance than S/PDIF. This states the lack of "high quality" USB units on computers. Has this changed?

 

Reply
post #15 of 16
1/23/12 at 8:43pm

It all really depends on the quality of the usb input on the dac. Asynch usb has made it a good choice more often, but it all comes down to the design of the input. Does it isolate the 5v line and power the usb chip from the dac, does it reclock it, is it asynch, does it support higher resolution. These are all things that can help make the usb better option if they are implemented correctly.

 

The best thing to do is try it both ways with your dac and see which sounds better. If you cant tell the difference, than count yourself lucky and do whatever is easiest.

Reply
New Posts  All Forums:Forum Nav:
  Return Home
  Back to Forum: Computer Audio
Head-Fi.org › Forums › Equipment Forums › Computer Audio › Sound quality difference: USB vs S/pdif optical digital output?