Dr. AIX's POSTS TECH TALK — 20 March 2014

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One of the members of the audio board made a brief comment during our conference call the other day that has been rumbling around in my head for a couple of days. He said, “I consider analog tape to be high-resolution”. I didn’t respond although I probably should have. We were near the end of the call and I knew that interjecting would be too disruptive. But I know that his simple statement…and the silence that followed…indicate that the ultimate direction that the committee will take. Many agree with him.

About four years ago, I wrote an article entitled, “Why Analog Tape Recording Can Never Be High-Definition”. I’d like to pull from the piece and publish it again on this site. No doubt analog tape believers will think I’m beating up on them but I’m not. My goal in all of my posts is to shed some light on the different formats with regards to specifications and fidelity AND share my personal experience with these formats. I’m not making this stuff up.

I should state right up front that I love my Nagra IV-S analog tape machine AND my QGB (a rather rare optional component that allows the Nagra to handle large reels…it’s actually quite valuable). Purchased in 1985, this machine has played a very large roll in my career and I continue to marvel at its design…both electrically and mechanically. If you’ve never seen one or had a chance to “drive” a Nagra, I can assure you it’s a very rewarding and tactile experience. That’s one thing that is definitely better about analog than a portable digital recorder.

The new iTrax 2.0 will offer first generation analog tape copies from the master sources…if that’s what a customer wants.

Analog tape recording is analogous to making moves using 35 mm film cameras. There is a quality of sound that you can only get by using an analog machine. Pushing levels past the available headroom on a piece of analog tape produces a type and color of distortion that engineers and producers seek. I get all that. But at the end of the day, the raw capabilities of analog tape recording and reproduction are incapable of achieving the dynamic range and frequency response of well-done HD PCM. And there are lots of other things that HD PCM does better than tape. These are facts.

How do I know? I still have the Nagra IV-S owner’s manual. It’s a well-written document with lots of charts and sections about the machine but it also includes sections about the challenges associated with the format in general. The facts about analog recording are in this manual.

Section 5 is titled, “Noise added to a Signal by a Tape Recorder”. It describes the types of noise that accompanies tape recording. Below is the section in the manual:

Like all other elements of an electroacoustic chain, a tape recorder adds noise to the useful signal. Manufacturers of both equipment and tape are constantly preoccupied with the problem of reducing noise to the lowest audible level.

Classification

To distinguish between the different sources the noise are classified into the following groups:

Group A Background Noise: It is present whether a useful signal has been recorded on the tape or not.

Group B Modulation Noise: It is apparent when a signal is recorded on tape and is proportional to the signal.

Group C Head Magnetization Noise: This is a modulation noise, caused by a DC signal recorded by a magnetized head. While it is therefore a modulation noise (B), it is continuously present (A), and therefore is classified separately (C).

Group A: Background Noise

In a high quality recorder, background noise is essentially due to the tape and the recorder manufacturer cannot do much about it, except by making it less annoying by raising the recording level (distortion compensating circuits of NAGRA IV-S) or by using recording standards that attenuate the noise (NAGRAMASTER standard).

Group B: Modulation Noise

Modulation noise is a specific shortcoming of the magnetic recording process and it can be caused in several ways, especially by tape vibration noise, amplitude modulation noise and head magnetization noise.

Tape Vibration Noise

The tap is not transported in a perfectly regular manner; its speed varies (wow, flutter and vibration) and the frequency of the variations may be quite high. The frequency of a sine signal of constant level is therefore modulated by speed variations. Wow and flutter are well known subjective experiences, whereas a high frequency vibration of the tape simply make the recording sound dirty. As the noise disappears with the signal, it is obviously a modulation noise.

The problem is very serious with equipment of simple design, having no mechanical filters or – worse – having pressure pads on the heads. The tape vibration noise in the NAGRA IV-S has been rendered negligible.

Continued tomorrow in Part II

[NOTE: There is a solo piano recording on the FTP site that was simultaneously done on analog tape AND at 96 kHz/24-bit PCM. Feel free to download it an compare for yourself the fidelity and other attributes. Keep in mind that this a copy of the master tape…first generation.]

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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. So, the HRA consumer experience could be “non compressed audio” ?
    Wow, let’s rediscover the post WW II technology!

  2. Unfortunately all of this revolves around the “old” business of reselling footage. Who dares today to make the investment of record from start to finish in true HD, and do not say, in multichannel? L. Perhaps in a portable medium or low quality equipment is not appreciated. But that took decades of auditions and moderately trained ear we appreciate the difference. Why not try really new markup. Worth, at least, consider the opinion of our friend Mark. Greetings.

    • Thanks Federico. The business has been successful and despite some ups and downs in the last decade, the music business is not going away. I’m just hoping that there will be a place for real high-resolution audio in amidst the older transfers.

  3. Hi Mark,

    This is an excellent discussion. I have owned CDs since the mid 1980s. They slowly took over from my analog LPs as my medium of choice. From my experience:

    1. CDs actually do “wear out”, and,
    2. FLAC files ripped from my CDs clearly sound “better” than the CDs spinning themselves.

    My dozen or so “worn out CDs” would slowly develop clicks and skips over time. Some have progressively gotten worse and stopped playing at the offending bits. In a way this was like the LPs of old, except that there was no increasing noise with each passing playback. Most of the worn out CDs are from the mid 80s and early 90s, but I do have some newer ones as well. The surfaces are spotless and without scratches on either side. There is no visible rot on my failed CDs. I take care of my CDs as well as I took care of my LPs so they were never abused, used in the car etc… Of course I have many hundreds of CDs from the 80s and 90s that are just fine.

    As I ripped all my CDs to FLAC files, I found that some of the CDs that I have not played for a long time, could not be ripped without errors. That was when I discovered how many have “worn out”.

    As for the sound quality of the FLAC files versus their CD “masters”, there is no contest. On better recordings the FLAC files were clearly better. Mind you, I am comparing against CD player RCA coaxial outs compared to a Bryston BDP-1 XLR out and into DEQX. I will refrain from the usual subjective audiophile jargon but, I was surprised that I could hear such an obvious difference with so many pieces of music. So in my case, the rationale is not important; it works for me and that is all that matters.

    • CD are carriers of digital data, plain and simple. I have hundreds of CDs that haven’t been played for many years. But if I pull one out of a box and play it, 99% of the time they exhibit no problems. They can and do get damaged AND they can suffer from “rot” but I’m unaware of them “wearing out” from simply playing them. I’d be interested in others comments.

      As for the differences between a ripped FLAC representation and a spinning disc, I believe you that you experience a difference. But it’s NOT because of the delivery of the data from the HD or disc…it’s the Bryston BDP-1 and DEQX boxes. I would say keep doing it. But you should know that the data is exactly the same.

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