USB-DAC

A very flexible solution is a USB-DAC as almost any PC offers USB.

Using a USB DAC you don't need a sound card at all.
If you use a laptop this is probably the way to go if you want to improve on the onboard sound card.

A clear and well written step by step guide to setup and USB DAC using XP, Vista or OSX can be found at the Ayre website.

Setup for Win7.

Setup for Vista.

Asynchronous USB 2 DACs

USB Audio class 1 is limited to 24 bits/ 96 kHz maximum.

This is what fits into USB Full Speed mode so 12 MHz (USB 1).

To play higher sample rates the High Speed mode (USB 2, 480 MHz) is needed.

 

From mid-2010 on both OSX and Linux supports USB audio class 2 natively.

If the DAC is USB audio class 2 compliant it will play up to 32/384 on these systems without the need to install additional drivers.

Microsoft doesn't have a native mode USB Audio class 2 driver. You need to install a third party Class 2 Audio driver at the PC side.

 

All DACs listed in this section requires USB 2 (High Speed).

The fact that they do need USB 2 (High Speed) does not necessarily imply they are also USB audio class 2 compliant.

A couple of models

24 bit Asynchronous USB Class One Audio DACs

These DAC’s are USB Audio class 1 compliant.
They can play 24 bits audio with a 96 kHz sample rate.

All major operating systems (Win, OSX and Linux) do have native mode USB Audio class 1 drivers.

A couple of models.

24 bit adaptive mode USB Class One Audio DACs

These DACs use the adaptive mode and are USB Audio class 1 compliant.

The audiophile community thinks asynchronous is the way to go.
So all of a sudden these DAC’s look obsolete.
However, as usual in technology, the implementation is very important.
A good adaptive mode implementation can beat a mediocre asynchronous implementation.
Some say that the difference between async and adaptive is simply marketing talk.
As faith would have it, prominent spokesman of these view are the ones making a living by selling adaptive mode implementations. Surprise….

A couple of models.

16 bit USB

Today you can buy a 24 bit USB DAC at an affordable price.
No reason to limit you to 16 bit anymore.

16 bit USB DACs can be found here.

Vendor specific

Some companies don’t use USB audio in isochronous transfer mode.
They implement their own solution using bulk mode transfer.
Bulk mode is asynchronous by design.

As it is bulk mode,

In case of isochronous mode it is exactly the reverse.

As long as the DAC is the only one connected to an internal hub, bandwidth is in general not the problem using USB high speed mode.

 

Inherent to a vendor specific solution is that he either supports your OS or not.
The advantage of USB audio is that it is natively supported by Win, OSX and Linux.
However in case of USB audio class 2 on Win you need a third party driver too.

Anyway this solution does audio over the USB without using the USB audio of the operating system.

 

References

More technical information about USB audio can be found here.