elianda wrote:What equipment do you use to measure the SNR ratio?
Ideally, some type of standalone audio analyzer, which seem to range in price between several hundred, and tens of thousands of dollars. Keyboard Magazine used an Audio Precision System One when they gathered statistics for a number of soundcards back in 1994. I haven't any guess as to what the Sound On Sound folks used.
What is the variation for SB16 cards of the same CTxxxx number?
This is the kind of information that would be great to have, but that no-one seemed to bother with delineating in their reviews.
The available information isn't particularly meaningful anyhow, unfortunately. On one hand, you've got the manufacturer-provided specifications, which were often based on best case figures provided in spec sheets, and on the other, you've got reviewers that tested, but did so using "default" installation configurations, where no effort was made to optimize mixer settings, or disable unnecessary inputs and (noisy) spatialization features.
To what extent is the origin of the noise the card itself (independent of the system) and what is coming from the systems PSU, bus etc. ?
I think it depends both on the card, and the system and slot placement in which it's installed. A noisy amplifier chip will obviously follow the card around, but in my experience, bus noise has only been particularly bad/noticeable in one or two compact systems that I own.