Pro's/Con's of USB DAC against Sound Card?
Feb 10, 2006 at 1:48 PM Thread Starter Post #1 of 5

maxxy

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Question is pretty self explainitory. Would like some insight as I have no clue why one would be better than the other.

Cheers
 
Feb 10, 2006 at 6:42 PM Post #2 of 5

Jon L

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Quote:

Originally Posted by maxxy
Question is pretty self explainitory. Would like some insight as I have no clue why one would be better than the other.

Cheers



Wow, this is a HUGE question. Short answer, in an ideal world, neither method is intrinsically better or worse. Now the long answer...


Soundcard Disadvantages

Low to moderately priced soundcards are built to a price point, using cheap parts and most (all) using op-amps to do everything, including output stage. They also use tried-and-true digital design, meaning standard oversampling/filter methods. You just aren't going to see non-oversampling, no-filter, TDA1543/41 types of digital design on soundcards. You also aren't going to see class-A, zero-feedback, discrete analogue output stages. Nothing 'wrong' with that, and many of these cards measure quite well, but the analogue outs usually sound, Ehem, unsatisfactory.

Another big (to me) disadvantage is that soundcards depend on computer's PS for clean power. This is a real problem b/c computer PS are not built with clean audio performance in mind. PC PS, along with many digital IC's inside the PC spew out RFI/EMI, which is not an ideal situation for any digital-to-analogue converter, including soundcards, but my feeling is that the computer RFI/EMI angle is somewhat exaggerated, mainly if the soundcard has been properly engineered to combat this. For example, one audiophile audio server manufacturer told me that they tried the Lynx card with battery vs. PC PS, and the Lynx sounded basically the same b/c Lynx was designed to work well despite the RFI/EMI environment. Then again, Lynx is not exactly cheap.

I also don't like the fact many soundcards have output interfaces that require modding to sound best. You often have to battle 1/8" 1/4" stereo output jacks, proprietary DB25 type of breakout cables, which universally sound unsatisfactory. For example, I wouldn't pay $100 for the Lynx card if I was forced to use its stock, awful-sounding, long breakout cable. Use a quality, DIY analogue output adapter, and you are in an entirely different universe.


Soundcard Advantages

I feel that the PCI connection is an unfairly overlooked option for state-of-the-art digital music connection. People have struggled long and hard to improve the evil that is spdif and run-of-the-mill USB music connection. PCI connection is a great-sounding digital connection method for music that avoids the dreaded spdif connection, and even the cheapest soundcards enjoy this advantage.

Just about the only company that has fully taken advantage of the PCI connection is VRS audio, who uses modded Lynx card with PCI connection in their $10K+ audio servers. These sound fantastic, not being a limiting factor in Shindo Labs audio systems they often demo with.

Still, unless you are prepared to go all-out with soundcards, the better use of soundcards is as digital-out solutions into outboard DAC's.


USB DAC Disadvantages

Despite the promise of bit-perfect, low-jitter USB music connection, the vast majority of USB devices/DAC's fail miserably. The holy grail of USB connection will have to have all of the following:

1. Asynchronous USB protocol--the best, lowest-jitter method, but I'm not aware of ONE USB DAC on the market today that uses asynchronous protocol, not one. Most consumer devices use the worst synchronous method, which are in fact worse than the usual spdif method. The better ones use "Adaptive" mode, which can sound better than spdif, but it's still not as good as USB can be.

2. Direct USB-I2S-DAC connection. Most USB DAC's USB chips convert the signal back to the dreaded spdif, which is then sent to the usual CS spdif input receiver chips, completely negating the benefit of USB (supposedly spdif-free) connection. Fortunately, more and more small companies are starting to use I2S connection using the PCM2706/7 USB chips, such as the new Scott Nixon USB DAC, DDDac, Empirical Audio, but these are far and few between.


USB DAC Advantages

USB digital connection 'can' sound better than spdif, provided the caveats listed above. Despite my disappointment with current state of USB connection today, I have high hopes for future USB DAC's, especially if TI decides to market new USB chips designed for audio, with native asynchrouns protocol support. That'll make my day (year, decade)!

Also, as mentioned above, unlike soundcards, USB DAC's have no limits as to how elaborate the designer can go as far as internal parts quality, power supply quality, etc. Sky is the limit.


The Future

PC audio will have come of age if all of the above criteria are met, and if even the cheapest, standard PC ships with native asynchronous USB support, enabling the use of high-quality direct USB-I2S DAC's. I personally look forward to this future, and there are little signs here and there that hints the future may not be that far off.

In the meanwhile, for the present, I believe the best compromise is to use a high-quality soundcard's digital output (possibly modded) into an outboard DAC with good jitter-rejection circuitry. Another way is to buy a USB DAC that at least uses adaptive mode USB protocol and direct I2S connection.
 
Feb 10, 2006 at 11:59 PM Post #3 of 5

RockinOut

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I like a USB/optical standalone DAC more than a sound card mainly because it can be more versatile especially at low- and mid-budget rigs. You can use it with any number of laptops, desktops, and transports in conjunction with a decent headphone amp. It allows many options in rig setup and changes--improvements upwards or laterally.

I like the optical input better because in my own rig I had problems with USB ground/power noise. I ended up having to use my amp on battery power to get rid of the hum when using USB.

I like the setup I'm using. It's mid-budget, sounds wonderful--good enough until my next major upgrade--and is reasonably transportable in a duffle-sized, padded bag, and everything can run on battery power.

I'm sure sound cards can sound great and ultimately sound better. But that's it, you're stuck to your computer.

USB DAC and laptops, I think are the inevitable "next step" for many HeadFiers because many of us came here from the growth of the mp3 player market, especially with the ubiquitous Ipods, itunes, and notebook computers all around us.

Here's another good thread on this subject of USB DAC:
http://www4.head-fi.org/forums/showthread.php?t=162717

Cheers. This place rocks.
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P.S. A USB/optical DAC can also be used with the Iriver H120 for even a smaller footprint. Just more choices $$$$
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I really hate this place
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Feb 14, 2006 at 4:45 AM Post #4 of 5

Solitary1

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Quote:

Originally Posted by Jon L
People have struggled long and hard to improve the evil that is spdif and run-of-the-mill USB music connection. PCI connection is a great-sounding digital connection method for music that avoids the dreaded spdif connection, and even the cheapest soundcards enjoy this advantage.


I'm sorry, but I guess I missed something. What is so dread about SPDIF? I've used it since the mid-90's to transfer DAT recordings to my Macs. Not perfect, but what is? Get your clocking and your sampling rate right and good to go.
 
Feb 14, 2006 at 7:41 AM Post #5 of 5

tschanrm

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Quote:

Originally Posted by Jon L
USB DAC Disadvantages

Despite the promise of bit-perfect, low-jitter USB music connection, the vast majority of USB devices/DAC's fail miserably. The holy grail of USB connection will have to have all of the following:

1. Asynchronous USB protocol--the best, lowest-jitter method, but I'm not aware of ONE USB DAC on the market today that uses asynchronous protocol, not one. Most consumer devices use the worst synchronous method, which are in fact worse than the usual spdif method. The better ones use "Adaptive" mode, which can sound better than spdif, but it's still not as good as USB can be.

2. Direct USB-I2S-DAC connection. Most USB DAC's USB chips convert the signal back to the dreaded spdif, which is then sent to the usual CS spdif input receiver chips, completely negating the benefit of USB (supposedly spdif-free) connection. Fortunately, more and more small companies are starting to use I2S connection using the PCM2706/7 USB chips, such as the new Scott Nixon USB DAC, DDDac, Empirical Audio, but these are far and few between.


USB DAC Advantages

USB digital connection 'can' sound better than spdif, provided the caveats listed above. Despite my disappointment with current state of USB connection today, I have high hopes for future USB DAC's, especially if TI decides to market new USB chips designed for audio, with native asynchrouns protocol support. That'll make my day (year, decade)!

Also, as mentioned above, unlike soundcards, USB DAC's have no limits as to how elaborate the designer can go as far as internal parts quality, power supply quality, etc. Sky is the limit.


The Future

PC audio will have come of age if all of the above criteria are met, and if even the cheapest, standard PC ships with native asynchronous USB support, enabling the use of high-quality direct USB-I2S DAC's. I personally look forward to this future, and there are little signs here and there that hints the future may not be that far off.

In the meanwhile, for the present, I believe the best compromise is to use a high-quality soundcard's digital output (possibly modded) into an outboard DAC with good jitter-rejection circuitry. Another way is to buy a USB DAC that at least uses adaptive mode USB protocol and direct I2S connection.



Jon L,

I agree with a lot of what you said about PCI sound cards. I think budget PCI sound cards are more of a value than budget USB sound cards. When you get into high end recording sound cards, it really depends on the implementation of the components. For instance, Lynx have well regarded PCI sound cards, but Digidesign/Edirol/RME also make very good USB/Firewire cards as well. I think one of the more moddable sound cards out there right now is the EMU 1616m, simply because it is an external sound card with an external power supply, getting data sent to it from the PCI bus.

Some of the disadvantages about USB you discuss have been talked about before. First, there is a USB sound card that uses Asynch playback mode. ThomasPF in this post claimed that the Audigy2NX uses asynch audio mode:

http://www4.head-fi.org/forums/showp...6&postcount=11

However, back in October of 05', 00940 had evidence that asynch. audio transfer over USB for windows was flawed:

http://www4.head-fi.org/forums/showp...2&postcount=13

In fact, to quote directly from that article:

Quote:

Starting with Windows 98, Usbaudio.sys supported the adaptive and synchronous endpoints, but it did not implement the asynchronous endpoint correctly. Full support for asynchronous endpoints in Usbaudio.sys is planned for Windows Longhorn.


So this answers the question why almost nobody has used asynch for USB audio. Longhorn, now called Vista, will be the first windows O/S to properly implement asynch mode. You could use another O/S besides windows, but the market designs hardware to work with the most popular O/S: Windows. Maybe when Vista is released you will see some USB cards with asynch mode.

The pcm2706 that you mention, and the TUSB3200 use the adaptive transfer mode in USB, which provides very low jitter levels. This method uses the converter chip's clock to control the rate of data sent, similar to Sony's I-link. ThomasPF points out that adaptive transfer mode pulls data asycnhronously from the sender:

http://www4.head-fi.org/forums/showp...71&postcount=9

So really, adaptive transfer mode uses asynchronous, with jitter depending on the quality of clock used. This means that the USB bus does not add any jitter to the system. Using a direct asynch playback mode may not yield any jitter improvements over adaptive transfer playback mode. ThomasPF and I had some discussions about USB and jitter, which can be viewed in these two threads:

http://www4.head-fi.org/forums/showthread.php?t=134969

http://www4.head-fi.org/forums/showthread.php?t=140793


More on-topic, this post from DIYHiFi reveals that jitter on the PCM2706 is lower than s/pdif using a CS8412:

http://www.diyhifi.org/forums/viewtopic.php?p=6869

All in all, USB and S/PDIF are just different methods for sending bits. S/PDIF and USB can both have low jitter levels, it's just that USB can implement the low jitter level in a more cost effective way (i.e. less parts required).
 

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