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.
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.]