15 ips Analog Tape

Since when did a 50-year-old analog format become the standard bearer for state-of-the-art music recording and reproduction? I’m reading the reel-to-reel groups, attending the DSD presentations at the Newport Show and am well aware of The Tape Project and now The Master Tape Sound Lab. Somehow, there is this notion that a 15 ips 1/4″ 2.0 channel stereo analog tape is the “holy grail” of audio reproduction. That level of fidelity (which I appreciate and spent many years doing) is expected to be the goal for all engineers and record producers. It’s time to take a closer look and inject some reality back into the merits and limitations of analog tape.

Yesterday, I mentioned an article at HighFidelity.pl that featured the Polish company, The Master Tape Sound Lab, and its founder Todor Dimitrov. The opening line of his website states, “The revival of reel to reel is, paradoxically, related to the digital revolution that takes place right before our eyes, i.e. the transition from physical media to computer files. But it is not only and merely nostalgia – analog tape still remains the best known musical medium. Even vinyl is merely an attempt to approximate what can be found on 1/4 inch analog tape played at 15 ips.”

It is not my intention that this post be a roast of the analog tape format. In fact, my plans include releasing some test analog transfers of my PCM HD-Audio masters using some pretty amazing equipment (Benchmark DAC2, Nagra IV-s). I plan to create and circulate an AIX analog tape to a few interested listeners and a few of the clientele of The Tape Project to get their reaction. I spoke to my friend Paul Stubblebine (one of the principals TTP) at the recent Newport Show about collaborating on a series from the AIX catalog. He and I think it’s worth exploring. I recognize that analog tape has a distinct sound AND that there are advocates that enjoy that sound above all others. I believe my unique recording process will work well in the analog domain.

But it’s quite another thing to claim that analog tape is the “best known musical medium”. It’s merely format among many that has been around for a very long time. Because of its longevity, there are many tens of thousands of multitrack and two-track analog masters that represent the core part of our musical heritage. From the “Golden Age” of the late 50s and early 60s to the projects that are still being recorded on analog tape, there is a very rich catalog of inspired music making available for licensing and distribution…in a variety of new formats.

But there are very real (pun intended) limitations with the format. Here are a few:

1. The dynamic range of a traditional 2.0 channel analog tape machines running at 15 ips is about 60-72 dB SNR (without noise reduction). The dynamic range of human hearing extends to around 120-130 dB (the “threshold of pain”)…and remember this is not a linear scale. The exponential nature of decibels means that human hearing can accommodate sounds that are billions of times louder than the “threshold of hearing”…the quietest sound we can perceive. We do much better with our hearing than any other sense. For comparative purposes, HD-PCM at 96 kHz/24-bits can reach 130 dB SNR in practice and even more in theory. Which format would you choose if you were asked to record Mussorgsky’s “Pictures at an Exhibition” as orchestrated by Maurice Ravel? If you chose analog tape you’re going to be limited by the dynamic range and have to use a compressor. (If you haven’t heard the last section, “The Great Gates of Kiev”, add that to you must listen to list!)

2. The frequency response of analog tape is not ruled by the Nyquist or any other theorem…merely by the speed of the tape, the width of the head gap and the formulation of the tape being used. All analog tape machines use something called bias to assist in the process of converting analog electrical signals to magnetic domains on a Mylar strip of tape. It is an ultrasonic signal (typically between 50 – 150 kHz) added to the main program material. The idea is that this bias frequency is so high that end users will never hear it. I remember hearing it when moving a piece of tape slowly across the P/B head of an editing machine. It’s a squeaky pitch that exists above the rest of the program. It’s there at very low amplitude. In fact, the high frequency capabilities of analog tape diminish rapidly after 20-30 kHz and continue to roll off as you get close to the bias frequency. HD PCM audio at 96 kHz delivers better HF response in spite of the ceiling of 48 kHz due to the Nyquist frequency.

3. Crosstalk, modulation noise, printthrough, wow & flutter and other issues are also problematic with analog tape recording. Magnificent engineering…both electrical and mechanical…has minimized these, but they remain bigger problems than jitter and quantization noise.

4. Multichannel music delivery is another area that is personally very appealing to me and which doesn’t exist in consumer analog tape distribution. There was a time when quadraphonic tapes were produced and distributed by they were short-lived. PCM systems are not limited by channel count…there are 5.1, 7.1 and even 11.1 soundtracks being commercially distributed today! Analog tape is a 2.0 channel stereo medium.

5. The long term viability of analog tape machines is extremely limited. There are companies that are in the business of refurbishing older consumer decks and selling them for outrageous sums but no one is in the business of manufacturing new analog tape machines. The days of Ampex, Revox, Nagra, Stellavox or others are over.

So analog is a wonderful niche market for a small group of dedicated followers. I’m hoping to impress this very group with my “first generation” master tapes. But when someone on a DSD panel states that hearing a 15 ips stereo analog tape transferred to DSD 64 or 128 is “audio nirvana”, I have to ask if they’ve ever heard a real HD-Audio track in fully immersive 5.1 “stage” perspective surround? The difference is amazing.