Originally Posted by judmarc
So - headroom because we don't have infinite time, and headroom because of the real-world limitations of filters ("brickwall" bandlimiting produces audible artifacts if done near 44.1kHz). But notice that we are no longer in the realm where we can settle back and say "Good! A little headroom and now we can do perfect reconstruction under Nyquist-Shannon." We can only make a better (in practice very good) approximation, and use filtering that won't harm the audio signal as much. So we can't say with mathematical certainty we've reached perfection at 96kHz and no more improvement is possible. To use your analogy, we've made a better (but not a perfect) vacuum, so the speeds we measure for photons are a better approximation of the theoretical limit but not mathematically equal to it.
Can we make an audibly better approximation at 176.4 or 192 than at 88.2 or 96? Some people think so, some don't; I don't know for sure. But I haven't seen anything that tells me we must absolutely foreclose the possibility.
We don't want to doom ourselves to repeat the history of "perfect sound forever" by ignoring what happened then. What happened? It seems to me we thought our "very good approximation" of Nyquist-Shannon was so close that for practical audio purposes we'd achieved perfect reconstruction, or as near as it was possible to get. We thought so strongly enough that many folks were willing at first to ignore audible evidence. Later of course the audible became measurable (e.g., jitter, "brickwall" filtering, and resultant distortion in the audio band).
I missed this post before and you make some good points, although maybe a little inaccurate in some of your statements.
I agree with jcx. It is not accurate to say that the science and the pro audio community thought CD was perfect and then found ways to measure the imperfections. Accurate scopes existed in the early 80's, the weakness of digital audio implementation was well known (both measured and audible) and the CD Redbook standard was hotly contested at the time. Despite the known weaknesses, CD was marketed
as perfect. Again, as jcx states the whole thing was commercial/political, with the manufacturers winning out. For this reason, the perfect digital audio playback format does not even exist! The perfect balance of speed vs accuracy for the consumer would be about 16bit 60kS/s. You are making a mistake which is rife in the audio world, confusing the marketing of facts with the actual facts. It was for this reason more than any other than I started this thread!
Have we now reached perfection according to Nyquist/Shannon? Depends on how you define perfection; mathematically no we haven't but perfection to the point of substantially exceeding the ability of the ear to detect, yes. DACs have existed for quite a few years which measure a linear response to a point far beyond audibility. Jitter, such a problem according to much marketing, is a non-issue with any decently designed DAC. To the point that highly expensive, high precision equipment is needed to be able to measure it (at the point of the AD or DA chip) and orders of magnitude below what is audible. Bit depth (dynamic range) has already exceeded not only the ability of the human ear but even the laws of physics. Despite DACs being marketed as 24bit no DAC on the planet can actually resolve more than about 21 bits. A dozen or so years ago 18 bit was about the maximum technology was capable of resolving but at 21bit the limit is no longer technology but the laws of physics, so this is never going to change. That doesn't seem to have stopped the latest fad of marketing 32bit DACs. If 32bit dynamic range was actually possible it would kill you instantly! The same is true of sample rate, although fortunately you can't be killed (or injured) by higher sample rates.
By far the biggest problem facing the digital audio world today is actually the consumer and the manufacturers' ideas of what the consumer wants!!!! Rather than stopping at the point of digital audio perfection we just keep on going, apparently oblivious to the fact that we've missed the stop and are now travelling further and further away from where we should have got off. Audibly perfect DACs have existed for some time but the development of technology to make that level of perfection cheap and ubiquitous is a dead end road for marketing departments.
So am I saying we have reached the end of the road for better quality audio? Not at all! On the technology front there is still improvement to be made; with digital the cheap availability of audibly perfect DACs but even more can be done on the analogue side, particularly with transducers and acoustics for example. But dwarfing just about all other considerations put together, the biggest improvement by far which can be made is with the consumer. There are several areas for the consumer which need improvement if audio quality is to be increased:
1. The realisation that the experience of a live musical performance is not dependent on sound waves alone and therefore will never be captured or reproduced by digital audio technology.
2.. The ability of the consumer to appreciate, demand and pay for higher quality music products.
3. A demand for higher quality equipment at reasonable prices rather than for equipment with bigger numbers.
Point 2 is particularly important. The consumer has demonstrated that in general it is more interested in low or no cost, than it is in quality. The demand for MP3s at prices of $1 a song and for those MP3s to be as loud as possible (or indeed most of the time, IMO, louder than is possible). Obviously I'm talking about the consumer in general rather than the relatively niche audiophile market. Audiophiles though are more responsible for points 1 and 3 above. It seems to me that many audiophiles (maybe even a majority) do not want perfectly linear systems, they want distortion. Presumably because of past experience of other sound systems (consumer systems and/or live sound re-enforcement systems) many audiophiles do not seem to measure the quality of a sound system by it's linearity of reproduction. Preferring instead warmth, HF distortion, noise, etc. The love of vinyl, tubes, coloured cans and speakers, filterless DACs, etc., is proof of this. I've seen descriptions from audiophiles about DACs (or other equipment) such as too analytical, too detailed or too clinical. A DAC can't produce more detail than exists in the recording and cannot therefore be too analytical or clinical. The audiophile is basically saying they don't like the sound of linear reproduction. Many audiophiles seem to be highly influenced in their appreciation of what constitutes quality by marketing tactics such as pseudo science, shills and reviewers with advertising revenue at stake. Therefore, I'm sure some (if not many) will find what they are looking for in 24/192, the upcoming 32/384 and presumably in 64/768 (as soon as someone finds a way to make it available for marketing).
The relatively few knowledgeable audio professionals and audiophiles just do not represent a big enough consumer marketplace to make linear playback and high quality recordings anything other than a minority of an already niche market. Until real quality (rather than a marketing led concept of quality) becomes profitable we are going to see a continued decline in the quality of recorded music and movement further and further away from the Nyquist-Shannon ideal of digital audio recording and reproduction. Virtually none of the world's top commercial recording studios make an operating profit. If the current trends continue, it won't be so long before the music industry looses the knowledge, skill and facilities required to make a high quality music product, maybe forever or at least until real quality becomes fashionable (profitable) again.
GEdited by gregorio - 9/15/11 at 2:14am