ORIGINAL: attalus
I have no doubt converters play there role but i'm sure aswell that the 192khz extra bandwidth plays it's role aswell.I'm sure the same is with the neve 88D 40bit processing and the SSL beyond 192khz bandwith aswell, Im sure they convert better, but i'll bet my right arm that they just plain sound better overall.In the end you have a good point but i'm pretty convinced soundcards can always be improved, and at this point i believe 32bit would be a hearable difference if the converters and the rest of the card is built well!
Yes, soundcards can always be improved, but at this point, 32-bit soundcards just plain don't make sense.
The A/D converter in a soundcard essentially converts voltage in the wire into a number. The range of numbers depends on the bit depth. 24-bit audio has 2^24 or 16,777,216 different possible values. The so-called "professional" audio level operates at a nominal level of -4dBu, which equates to only a bit over one volt. This is just the "nominal voltage", though - something of an "average". The actual peaks can be much higher. Say the A/D converter can handle 5 or even 10 volts maximum.
Divide this into 16,777,216 pieces, though, and each piece ends up being extremely tiny - easily less than a microvolt. In order to really sample sound at a true 24-bit resolution, the A/D converter would need to be able to accurately detect changes of less than a microvolt.
It turns out that it takes some pretty impressive electronics to achieve this feat. Changes of a microvolt can easily be caused by a variety of sources, including magnetic interference, fluctuations in the power source, and even moment-to-moment temperature changes inside the electrical components. This means that it would be very difficult at best to get any soundcard to work at a true 24-bit resolution inside of something like a home computer.
Essentially, what happens is that noise inside of the system covers up the really fine details. Imagine feeding a steady signal into a 24-bit A/D converter such that the A/D converter should theoretically read a constant 5000. At the voltage levels of audio systems, the actual result would not be a constant 5000. The value would randomly jump around 5000, sometimes reading above, sometimes below. Oversampling can help remove some of this variation and correct for some of the noise, but not all of it. If we convert the readings to binary, we may notice that the first 20 bits of every value are always the same. However, those last 4 bits just jump around, basically randomly. This means that our soundcard is really giving us audio with an effective bit depth of 20 bits, because those last 4 bits of resolution are covered up by random noise.
As it turns out, the absolute best of the soundcards most of us on this forum use get an effective bit depth of not much more than 20 bits. Well, actually, the sound may sound a bit better than something dithered to 20 bits, because of an interesting phenomenon where the human brain can identify sounds lower than a noise threshold. (This is the ability that sometimes causes people to think they hear voices in white noise - the human brain tries to discern the sound beneath the noise floor, even if there's no sound there.) Essentially, the brain can make out some of the gist of the sounds hidden in those lower 4 bits, even though they are mostly masked by noise. But for all practical purposes, the effective dynamic range ends up being roughly 20 bits (or approx. 120dB).
The Neve console you mention is a different beast. It is completely custom-designed with high-end audio in mind. So, it can have all kinds of custom features designed to minimize noise in the A/D converters, such as special power supply, special housing, and of course, a high-end converter. But even that Neve console is only 96/24. It just may have an effective bit depth of something closer to 24 than the soundcards most of us work with. It may even have an effective bit depth of pretty close to 24. But obviously, you need to pay for that.
But getting back to computer soundcards... Since the best of them are still rather far from actually using all 24-bits, it would be an utter waste to build one that was 32-bit, at least right now. Especially since A/D converters tend to get geometrically more difficult to make as resolution goes up. In other words, it is not 50% harder/more expensive to build a theoretical 32-bit soundcard, but many, many times more expensive. And if the effective bit depth stays at 20-bits because of electronic noise, it is even more of a waste. The perceived performance of the 32-bit soundcard would be identical to that of a 24-bit soundcard, and both would be getting almost the same results as a 20-bit soundcard.
Since one of the main problems with increasing bit depth is that the voltage changes are too small to be measured over the electronic noise, it seems one option might be to raise the voltage level in the analog lines. But this means that a new analog audio standard would have to be developed, like a +20dBV standard or something. But this would have a ripple effect throughout all audio electronics - every piece of analog equipment would have to be built to handle higher voltages, which means better (i.e. more expensive) power supplies and other components, which means EVERYTHING will cost more...
And then there's the fact that sound quality depends on more than just bit depth. The quality of the low-pass filters, the oversampling algorithm, and the stability of the timing crystal are also of critical importance. It would do no good to create a 32-bit soundcard if jitter in timing kept the effective bit depth at 20. And then there's the D/A converters, which have basically all the same problems in reverse. Getting a D/A converter to run at higher than 20-bits is just as hard as getting the A/D converter to do it.
Then there's also the question as to whether or not 32-bits is really worth it at all. 16-bit audio can only encode a dynamic range of 96dB. The human ear can discern a range of 120dB. This means that the range of human hearing is roughly 16 TIMES greater than the dynamic range of a 16-bit CD (24dB greater dynamic range = 16 times the dynamic range). It's no wonder that the sound of 16-bit audio is noticeably lacking, compared to real life. The dynamic range of 24-bit audio, however, is 144dB. If you recorded both the absolute quietest sound you could and the absolute loudest sound you could using 24-bit audio, then played it back on a system with true 24-bit D/A converters and speakers to match so that the absolute quietest sound registered 0dBspl (which, by definition, is the absolute quietest sound that the "average" human ear can hear), then the loudest sound would be way above the average human's pain threshold, a good twice as loud as a jet engine. A more practical choice would be to play the absolute loudest stuff at a more reasonable volume, which means any noise or distortion in our recorded tracks would be WAY, WAY, WAY below the threshold of human hearing. And this is just with true 24-bit audio. If the error with 24-bit recording is so far below human hearing that there's no possible way it could be discerned, what's the point of recording at 32-bit?
(Keep in mind that the record bit depth should not be confused with the bit depth for processing. We always want our intermediate results to be at a higher bit-depth than either our starting point or our desired ending results. That way the accumulated error stays at a minimum. If we round or truncate to 16-bit or even 24-bit after every mathematical operation, the distortion becomes apparent rather quickly during processing. So processing our audio with 32, 40, 48, or even 64 bits of precision is desirable, even if we only record at 24-bit. Recording at 32-bit would imply that we would probably want at least 48-bit or 64-bit processing.)
At some point the electronics might improve to the point that common soundcards can actually operate at true 24-bit, even if the nominal voltage levels of the analog signals don't change. Or, the audio industry might even adopt a new standard (undoubtedly not anytime soon), and increase the analog voltages. But until then, recording at 32-bit doesn't make any sense at all, if it ever will make sense.