Wednesday, March 14, 2012

Evolution of the High End, Part 2

Last time, we left off at the introduction of the compact disc and barely mentioned the huge success of this format in passing. Compact discs saved sagging music sales and in general the entire audio industry. So for this, I am grateful!

But now, time has come for this to mature. In my other article about digital format wars, I mentioned that the original 16/44 sampling rate was not exactly perfect audio as almost everyone, myself included, hoped it would be. Everyone pretty much agrees that the dynamic range of a CD is just not enough considering that micing a rim shot on a snare drum produces 135dB at one meter. So to capture life without the problem of the 16-bit word going "deaf" (the sudden disappearance of slowly decaying echos), AT LEAST a larger word size is needed.

But why was the original format chosen in the first place? Two reasons: the original total storage capacity of a compact disc (640MB), the longest performance you want to record uninterrupted before switching discs (about 60 minutes).  Adding to these two limitations is the sampling frequency (44.1KHz using the Nyquist Theorum for the minimum number of samples to be able to reconstruct a sinusoid). No one questioned this mathematical proof since it was also confirmed by Shannon as to its accuracy. So 44.1KHz it was.

From here, the math took over to determine the maximum dynamic range (word size) but you were left with an option that did not make the cut: compression. The math calculated a usable dynamic range of 90dB (96dB theoretical maximum) without compression (aka 16 bits, or exactly two 8-bit bytes) and engineers believed that this would be good enough compared to the maximum dynamic range of a vinyl record (78dB was the loudest ever recorded by Sheffield Labs). 16 bits was 12dB greater and people assumed that it would be more than adequate. So the math is:

44,100 samples/(channel*second) * 2 bytes/sample * 2 channels * 60 minutes * 60 seconds/minute = 635,040,000 bytes

Since its conception, CD capacity has grown to about 784Mb increasing the maximum playing time of 16/44 from 60 minutes to 74 minutes, uncompressed.

Marketing of all major record labels insisted that once a decision was made as to the digital playback format that it would not be changed (I forget what the length of time was but 20 years sticks in my gut). All agreed and the rest is history.

So without even listening to their conclusions, engineers went to work cobbling together the entire industry, both record and playback, based on these purely mathematical assumptions (what was it that someone said about assumptions?). And today we are still living with those initial left-brained decisions. If you've been reading my blog, you know how I feel about a decision that is made entirely from your left brain.

But now, the right-brained people are having their say. Musicians, producers, and audiopphiles alike are all about to "spit or go blind" when it comes to the future of digital audio. The Blu-Ray disc, with its infancy in 2002, created a storage medium exactly the same physical size as the CD but with over 7 times the storage capacity. Now that's what I'm talking about!

With 7 times the capacity (4.7GB vs. 640MB), new options present itself. What would be a good choice for the new digital format? If the word size (dynamic range) increased from 16 to 24 bits (2 bytes to 3 bytes), the usable dynamic range will go up from 90dB to 124dB (144 theoretical maximum). So now we can just about capture that snare drum I talked about earlier. So 24/? it is. I have listened to 24 bit recordings and although they are much better, there is still the fact that even this sized word goes deaf.

Great! But how much space do we have left for the increase in sampling frequency? Again here the math takes over and the numbers crunch out for each to be:

24 bits: (3 bytes/sample * 2 channels * 60 minutes * 60 seconds/minute) / 4.7GB = ~192000 
32 bits: (4 bytes/sample * 2 channels * 60 minutes * 60 seconds/minute) / 4.7GB = ~128000

So the two possible HD Audio formats on a Blu-Ray disc could be 24/192 or 32/128. My vote would be 32/128.

If we cut the playing time to 48 minutes, we get Ultra HD.

Ultra HD: (4 bytes/sample * 2 channels * 50 minutes * 60 seconds/minute) / 4.7GB = ~192000

BUT - and there is always a but - now the marketing folks want to toss in more than two channels and that is the big gotcha (there is more money behind the marketing types than the audiophile types). If we go from 2 channels to 8 channels (7+1), we are pretty much back at the beginning with 16/88 (same deafness problem but better high frequency resolution).

So it appears that audiophiles will lose again unless we all make our voices heard. This time, we have a chance to make a difference. Contact everyone you can and express your interest in making Blu-Ray High Resolution Audio in the format you prefer. Hopefully, your preference will be like mine: Ultra HD or 32/192.

Yours for higher fidelity,
Philip Rastocny

I do not use ads in this blog to help support my efforts. If you like what you are reading, please remember to reciprocate, My newest title is called Where, oh Where did the Star of Bethlehem Go? It’s an astronomer’s look at what this celestial object may have been, who the "Wise Men" were, and where they came from. Written in an investigative journalism style, it targets one star that has never been considered before and builds a solid case for its candidacy.

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