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Not Really...........

Posted by Todd Krieger (A) on July 14, 2009 at 16:31:03

In Reply to: Red Book Riddle Solved posted by J. Phelan on July 14, 2009 at 00:06:39:

"The advent of the Meridian 808.2 CD player and reviews in Stereophile and TAS of it prompted me to write this piece on standard resolution ('Red Book') digital audio. To be sure, advancements in playback have been very real over the past two decades. But with the advent of minimum-phase / 'apodising' filters and the massive improvement the brought to CD, a lot of people will be wondering if 16 bits/44.1kHz sampling was enough on disc, for playback."

This has been an ongoing debate..... In fact, the debate was "most-heated" in the early 1990s. (I remember debating this with the late Gabe Wiener.)

"The answer, after decades of debate and endless argument amongst audiophiles and audio writers seems to be YES - to this big question."

I think it's "no", based on what I've heard from CD relative to vinyl and DVD-A. (But DVD-A has other problems that I think are worse- very fatiguing.)

"Beyond mike technique, venue, etc. an encoding format has three main areas of concern: capture (sample rate, etc.) production and playback. Many audiophiles think there are only *two* main areas concerning a format - recording and playback. This is wrong - there's one more in the middle !!

"As it turns out, the areas affecting CD's sound were the last two - production and playback. The production problem was solved years ago and was an instant fix, as I show below. But first an overview: 16-bit digital encodes 95db of dynamic range - roughly 25db more than a large symphony orchestra produces. And orchestras produce far more 'range' than a rock band, jazz combo or string quartet - all of which have ranges in the 50's db. This fact links up with important findings in recent years by audio researchers. One of them is Bob Katz - Bob says that for original sources, 16 bits/44.1kHz sampling IS ENOUGH for all kinds of music. By 'original source', he means the encoded music before it was processed. This observation was derived from controlled listening experiments done over the years, that either Katz or others conducted."

I think the 44.1 kHz sample rate is more of a shortcoming for Redbook than the 16-bit wordlength........

"The problem as (all) recording engineers know, were the intermediate calculations done on the signal after recording - the 'DSP processing' done in production. With DSP, there were losses in a 16 bit recording - losses that eroded into the music - esp. symphonic-style and grand piano."

Everything with digital audio recording and playback involves "DSP".....

"But in the early 1990's a technique came along that cured the problem - 20-BIT RECORDING. This would absorb all the production losses that hurt 16 bit recordings."

The only thing 20-bit recording did was enable dithering off the master to the 16-bit media..... Dithering could have still been used in the original A to (16 bit) D process......... It IMO was more a marketing gimmick than anything else.

"Right after this, another technique called noise-shaping came out - another improvement - but this time for playback (on disc)."

Noise shaping was simply dither with a "frequency shaped" noise signal. (As opposed to plain white noise.) No big deal.

"As for the CD-standard, I quote Malcolm Hawksford from the March 1996 Stereophile article 'Bits is Bits ?': 'When correctly dithered using triangular PDF dither, a 16-bit digital audio signal possesses a dynamic range of 93.3db with zero distortion and zero noise modulation. The 16 bit format holds the possibility of even *higher* subjective dynamic range - up to 18db more - with minimally audible noise-shaping employed during CD mastering'."

The "zero distortion" is due to the harmonics being removed due to the 22 kHz bandwidth limitation. (It's only zero above 11 kHz.) It even removes distortion that was in the signal *prior* to digitization.

"Knowing this, why would *anyone* desire a new audio format ?"

Because a lot of the claims were more "spin" than reality. (There really is no such thing as "zero distortion".)

"Zero distortion, zero noise and dynamic range of 110db - that's 'not enough' ??"

If it were actually true...... The RFI from digital playback can be demonstrated by placing an AM radio near an active DAC. No system is totally immune to this noise. (This is why I prefer using optical connections to confine the RFI to the DAC portion of the system.)

"One of the arguments for more bits was that 'it's not the number of bits available but the number used at one time' (during recording). Yes, but that was a *production* issue - not a capturing or playback-disc issue !! The same goes for the sample rate - *if* more than 44.1kHz was needed, we got it, in capture - starting 16 years ago. The problem was that audio writers never explained the (true) virtue of 20-bit recording and that 16 bits might be enough, on disc."

Theoretically, 18 bits has been established as a minimum to encode recordings without dither. Dithering is not an exact science, and I would rather accurately encode of the signal at the lowest detectable levels using more bits than approximate the signal using dither and encoding to fewer bits.

"All this wasn't enough, however, as advances in playback were needed as well. But the issues in playback seem to concern the laws of electrical current and audio-chasis design much more than the 'band-aids' needed to improve CD sound. Yes, CD was 'upsampled' etc...but let's not forget that some CD playback systems *didn't* upsample and produced great sound
- like Zanden. In other words, most of the parameters concerning digital playback had to be improved anyway - no matter how many bits were on disc."

I'm afraid that while I agree the playback needed to be "improved", very few designers really have a good grasp regarding how to tangibly "improve" it.

"Tha said, it's not a surprise that CD sounds as good as it does today."

I think the playback sounds worse, by and large. A reason why there has been a new interest in vinyl playback. If the CD actually improved the way some have claimed, I really think vinyl playback would have been buried. Right next to 8-track.

"Some audio writers are struggling to hear a difference between the Meridian 808.2 CD player and true Hi-Rez audio. In this month's TAS, Robert Harley (strangely) did not compare the 808.2 with his Hi-Rez files. That's probably because CD sounds a lot closer to Hi-Rez than he thought it could (or should). But it's right in the specs......."

There are also people who have a hard time distinguishing CD from MP3.......

"These (new) observations are not a surprise to everyone. Below are four articles I dug up, starting with J. Gordon Holt in the mid-1980's and continuing forward. A little perspective and some solid answers is what we need."

I read the articles. I think the findings were more personal to his experiences than universally accepted.

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