Ok. I thought I understood the issues but now I'm quite confused. Isn't the digital output produced by a computer/sound card a mathematically determined sequence of bits? In other words, once an MP3 is decoded in software, shouldn't the spdif output be exactly the same regardless of what sound card is used?

I ask those that really know what goes on, because I'm doing research to purchase a good audiophile quality sound card (I'm interested in the analog output), and reading the reviews, I keep seeing reviewers evaluate the quality of the digital (spdif) output. As in, the spdif output with card x sounds way better on my stereo system with digital input than the spdif output of card y. Does this issue of sampling rates and convertions apply to digital outputs? I am talking about straight sound with no effects.

Can someone shed some light on this?

Some soundcard digital outputs are fixed at 48KHz. When playing back normal content at 44.1KHz, they have to resample. This makes the card sound less good than one offering genuine 44.1KHz, and also opens the possibility of some resampling algorithms sounding better than others.

Of course, some reviewers, both on the internet and in widely-read magazines, are charlatans and/or the victims of charlatans, and will offer qualitative comparisons of identical streams anyway.

Peter

Yup, samplerate conversion is important. Of course, so is the quality of the DACs on your digital amplifier.

Something else to worry about is digital bitstream jitter. This article explains it in good detail, and even specifically mentions sound cards in its discussion.

Thanks! Got it.

I have owned a USB based Onkyo SE-U55 sound processor for a while (I was using the analog outputs in an office setting, which are not too great). But this thing also has digital outputs and I am now using those to feed the Harman/Kardon receiver in my living room. I mostly play MP3s. The specs of the Onkyo say it outputs 32, 44.1 and 48khz. My MP3's are all 44.1 khz. I just can't tell from the literature and web searches whether the Onkyo goes 44.1-48-44.1, or whether it spits out the unchanged orginal 44.1 of the decoded MP3s (is there an easy way to test?).

For a while I thought going for a better sound option to feed digital to my harman kardon would be a waste of money. But now I'm not sure. I need a USB or FireWire based sound processor since i amd using a laptop (no PCI slot).

Thanks! Very interesting article about jitter. MORE CONFUSION!

Here's a forum with opinions on various cards.

http://www.hydrogenaudio.org/index.php?showtopic=16393&hl=sound+card

also: http://www.hydrogenaudio.org/index.php?showtopic=21331&

Other forums at this site also dicuss sound boards.

Thanks. There are some very interesting threads in that site.