Dr. AIX's POSTS — 12 July 2013

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I’ve had a fair amount of experience with recording media from an actual WWII vintage wire recorder to a rim drive analog tape recorder (my first tape machine) through the high definition PCM digital equipment that I use today. Each of these formats has a rather stringent set of specifications or attributes associated with it. One of the attributes is resolution.

For example, vinyl LPs and analog tape (and I suppose the vintage wire recorder) have “infinite” resolution according to supporters of analog formats because they store musical information as a continuously variable model of the original acoustic waveforms.

Digital recordings are by their very nature discrete representations of a waveform sliced into a multitude of samples. The number of samples varies greatly and gets tied in with the frequency response as defined by the Nyquist Theorem for PCM. The DSD crowd likes to say that a sample rate of 2.8224 kHz (or higher multiples of that number) actually approximates the “infinite” attributes of analog recording, but in reality anything that’s digital is discrete and can never be analog. All you have to do is look more closely at a very high sample rate.

I think it’s pretty obvious that “infinite” doesn’t fully capture the sense of fidelity that a format is capable of storing and reproducing. Is there something inherent in the analog storage and playback of music that guarantees superior quality? Of course not! So why do so many supporters of analog formats retreat to the simple-minded argument that if something is analog, it must be better than all other formats? As always, this has nothing to do with one’s personal sonic preferences! Everyone has the freedom to like what he or she likes.

Wouldn’t it make more sense to evaluate the entire process from recording through playback against various metrics? Even analog advocates acknowledge that there’s more to fidelity than just the “infinite” nature of the signal model being stored. Designers of analog recording system have had to contend with mechanical and electrical issues since the first machines were built many decades ago.

The accuracy of the mechanical systems can never be completely perfected so there’s bound to be shortcomings in the speed of the transport (wow & flutter), the intimacy of the tape to head contact due to dirt, grease, oxide shedding or edge damage or the scraping of a stylus or magnetic head across the recording media (a vinyl LP or analog tape).

Electrical signals are also subject to imperfections and distortion along the way. There’s harmonic distortion, self-erasure degradation, crosstalk, print through and clipping just to name a few. Even the finest circuits and components can’t completely remove these problems with an “infinite” resolution format.

And yes, the world of digital has it’s own set of issues…but they are different issues. We’ll talk about that in more detail soon.

But the bottom line is that the output of a digital to analog converter (especially the good ones that are used by audiophiles) is an analog signal has just as much “infinite” resolution as the output from a turntable spinning a vinyl LP! The process and storage of a selection of music in PCM or DSD digital isn’t reproduced as a discrete series of voltage steps that drive your amplifier and ultimately your speakers. The output signal is a completely smooth rendering (or should I say re-rendering) of the original analog signal that was converted to digital by the analog to digital converter at the other end of the process.

When someone says that analog formats have “infinite” resolution vs. the discrete “stepped” resolution of digital, it doesn’t mean anything. The output of either format is a smooth, periodically changing electrical signal.

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About Author

Dr. AIX

Mark Waldrep, aka Dr. AIX, has been producing and engineering music for over 40 years. He learned electronics as a teenager from his HAM radio father while learning to play the guitar. Mark received the first doctorate in music composition from UCLA in 1986 for a "binaural" electronic music composition. Other advanced degrees include an MS in computer science, an MFA/MA in music, BM in music and a BA in art. As an engineer and producer, Mark has worked on projects for the Rolling Stones, 311, Tool, KISS, Blink 182, Blues Traveler, Britney Spears, the San Francisco Symphony, The Dover Quartet, Willie Nelson, Paul Williams, The Allman Brothers, Bad Company and many more. Dr. Waldrep has been an innovator when it comes to multimedia and music. He created the first enhanced CDs in the 90s, the first DVD-Videos released in the U.S., the first web-connected DVD, the first DVD-Audio title, the first music Blu-ray disc and the first 3D Music Album. Additionally, he launched the first High Definition Music Download site in 2007 called iTrax.com. A frequency speaker at audio events, author of numerous articles, Dr. Waldrep is currently writing a book on the production and reproduction of high-end music called, "High-End Audio: A Practical Guide to Production and Playback". The book should be completed in the fall of 2013.

(5) Readers Comments

  1. It would be interesting if you could add to this post, or include in a Part II, an extreme close-up view of just a few milliseconds of the following wave form:

    [1] The analog output of the master file, played through the studio converters;

    [2] The analog output of a CD made from the above master file, played through a CD player;

    [3] The output of a vinyl LP made from the above master file or simply of the same music, captured at the output of a good RIAA phono amplifier.

    Choose a very, very quiet passage of music, approaching silence, where it is said (by the audiophile press and their readers) that 16 bit digital has high distortion levels that limits its accuracy and sound quality.

    Now that would be educational. 🙂 I expect it would be visually obvious which is the most limited format.

  2. Grant…I get where you going with your comment. If I understand, you want to examine the output of a native HD-Audio PCM file and then downconverted version of that same file to CD-Audio standard. Finally, you would like to see the output of a vinyl LP pressing of the same piece of music made from the HD-Audio file or possibly from an analog tape version of it. Have I got this right?

    While I don’t have the vinyl LP piece of this comparison, I probably could produce the first part of the comparison. I’m about to take a few days off…a short vacation to Detroit (Don’t make jokes…I grew up near there and still have lots of friends there!)…and will look at this down the line.

    I can say that the “approaching silence” areas of any recording are challenging. Analog tape for example can only achieve about 55-60 dB of signal to noise ratio while a CD can do 30 dB better…so the “approaching silence” thing is going to happen a lot sooner on the analog tape (or vinyl LP) than the CD.

    I’ll write a whole post about this in the near future…but the “high distortion levels” claim is a red herring. Sure the number of digital bits means that there’s more quantization noise happening at the reverb tails but it’s still way better than the alternatives and will dither the problem is practically masked entirely.

    • Hello Mark…. you are correct in your understanding of what I suggested. Although, without the vinyl component, I suppose it does not belong with this post topic. Although the vinyl sample would ideally be made from the same file, it could just as well be any vinyl that is of the same piece of music, e.g. a classical piece.

      The aim of my suggestion, and of using a very quiet passage, is really to pick an example where the amplitude of the musical signal is not burying the noise and distortion. To show how little is added by high resolution and standard resolution digital, and the contrast with vinyl.

      The choice of low amplitude signal would also counter the arguments of many critics of digital, who say CD quality audio is at its best at low frequencies and high signal levels, but ‘falls apart compared to vinyl or analog’ at high frequencies and low volumes — what they refer to as ‘the micro detail’. They say that with 24 bits and 192 or 384 kHz, digital is now ‘approaching analog tape and equalling or bettering vinyl LP’. I would like to point them to a view of the vinyl waveforms and say “You want *that* to be the goal of digital? Why?”

      cheers

  3. 16-bit, 44.1 Khz sound very very good. We established that much 19 years ago. Read the Whole thing at http://www.bostonaudiosociety.org/bas_speaker/abx_testing2.htm

    • Osomburk, you’re right that CD-Audio Redbook content can sound really great and in fact, is more than adequate for virtually all commercial recordings. However, the BAS ABX testing was so seriously flawed as to be meaningless. I talked about that in a post a few weeks ago at http://www.realhd-audio.com/?p=932.

      The fundamental mistake in the BAS “study” was that virtually all of the source recordings that were evaluated weren’t high definition recordings. If the materials that you’re testing don’t possess the quality that you’re looking for then how valid is the test? It’s no wonder that the participants couldn’t distinguish between the CD-Audio versions and the “so-called” high resolution versions…the HiRes versions were sonically that same as the CD ones!

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