For Audiophiles (Continued)

OpAmp Quality

Before the signal leaves a sound card after coming out of the sound card's DACs, it must be fed through some sort of buffer before it becomes remotely usable. This buffer also makes sure the DACs outputs aren't subject to any fluctuations that might cause trouble. You don't really need to understand the details behind the concept, but here's the gist of it.

The buffer is usually an operational amplifier (opamp) and this operational amplifier affects the quality of final audio output. These opamps usually lie in between the DC blocking capacitor and the DAC chip. They usually come in the form of a rectangular SO-8 chip package and have 8 legs. Any high resolution picture of the sound card you want to buy is enough to ascertain the markings on these chips, from which you can look up their data sheets with their performance numbers.

How do you read those nice performance numbers? I'll give it to you guys quick and dirty here :

Power Supply Rejection Ratio (PSRR) – This is the amount of noise in dB that the opamp can reject from the power supply. Higher is better.

Common Mode Rejection Ratio (CMRR) – This is the amount of common-mode signal in dB that the opamp can reject from from the signal. Higher is better.

Noise Density – This denotes the density of the signal noise. Measured in nV divided by the square root of the frequency in question. Lower is better.

Slew Rate – This is the measure of how fast the signal in the opamp can change. It is measured in volts per millisecond (v/ms). Higher is better.

Total Harmonic Distortion – Explained earlier, THD comes as a percentage. Lower is better.

ASIO Support

Although most might say that ASIO is only used by professional musicians and people that work with a lot of audio equipment, it does help you toy with the sound. This is because ASIO support allows you to bypass the Windows Mixer which can degrade quality to a small extent.

You should note that very few players actually support ASIO. One that I know is Foobar 2000. Although the level of improvement is debatable, the theory is sound. So, I'm just going to list it here, but I would not make it a major point when purchasing a sound card.

SPDIF Accuracy & Clock Jitter

For those like me whom use external DACs or external decoders, the most important thing is making sure that clock jitter on the SPDIF output is minimal at best. Testing for this without an oscilloscope is impossible and I don't know of any website that actually tests this metric, although I personally look forward to doing so. Right now, I will just list this here for knowledge's sake. There's no need to take this part too seriously anyway.

Okay, now that we're done with objective measurements of the sound card's performance for both gamers and audiophiles, let's move on to the features. I'll discuss the sound card's general features, both hardware and software, that one should look out for before making a purchase.