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Re: Need some feedback about what to buy

Posted by John Swenson (A) on April 17, 2007 at 11:50:13

In Reply to: Re: Need some feedback about what to buy posted by FranciscoHS on April 15, 2007 at 13:07:23:

I posted a nice detailed message on the subject yesterday, but it seems to have vaporized, so here is the quick and dirty version, trying to remember what I said!

Since you are running linux drivers are going to be a very big issue. Very few manufacturers write an ALSA driver, so you have to use what some volunteer threw together. This doesn't mean they are low quality, but it DOES mean that its usually very difficult to configure complex cards. You won't get the fancy GUI for setting DSP functions, 3d spatializers, mixer paths etc. Many of these items can still be controled but you you have to give a list of obscure options to set them. In many cases the only way to figure out what options to use is by reading the source code for the driver AND the datasheet for the chips involved.

Because of the above I highly recommend using the simplest devices you can find with the fewest possible options, you have a much higher probability of getting unmodified bits through to the output that way.

A simple USB DAC is very good in this regard because they can use the generic USB ALSA driver which works very well. The caveat with this is to stay away from devices that use the 1020 or 3200 USB audio chips, these require firmware and MOST implementations require that the firmware be loaded at power on. The generic USB driver does not know anything about this. There are programs which will load the firmware, but its an extra step you have to run at each power up. (On MAC and Windows there are device specific drivers that do the firmware load)

On your question on "USB soundcard" and "USB DAC" the result is the same, USB in analog audio out. The diference is that the "soundcard" is designed for computer users, gamers etc and has lots of "functions" othere than just outputting audio. A USB DAC is designed for audiophiles, its primary concern is high quality audio not the number of fancy features it can claim on the box.

There ARE some "soundcards" that have very good sound (they are usually not cheap though) but I would still not recommend them for linux use unless you really want to put in the effort to figure out how to correctly configure them from linux.

BTW irrespective of the device and driver, its important to use the right "interface" from ALSA. There are two primary an application can talk to alsa, the "hw" interface and the "plug" interface. Hw talks directly to the hardware and guarantees that the bits you put in are send to the hardware, the plug interface can modify the bits if it thinks it needs to (bit depth, sample rate conversions etc). So be sure to carefully check how your application is talking to ALSA, if its hw you can gurantee that at least ALSA itself is not mucking with the bits. (the application or the hardware might still be modifying things)

I hope that helps with the decision.

John S.

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