As We See It

While we were preparing our list of specifications for our perfectionist's tape recorder discussed elsewhere in this issue, we suddenly came to a screeching halt at the spec which started "Scrape flutter less than . . ."

What, we wondered, was the scrape flutter percentage in a recorder in which scrape flutter is audible? Would it be 0.5%? Or 1%? Or even 5%? We perused the readily available literature, and were informed that "scrape flutter is caused by the tape's tendency to move past the heads in a series of tiny jerks in stead of in a smooth gliding motion." We were also told that scrape flutter is due to friction between the tape and the head surfaces, plus the slight elasticity of the tape that allows it to stretch slightly before being dragged along by another silly millimeter, and that it sounds like a rough edge riding on all signal frequencies between about 3kHz and 8kHz.

But how much, we asked, was audible? And come to think of it, how did one go about measuring it? On these subjects, our research sources were of no help at all.

So, we resurrected the piles of old Audio Engineering Society Journals and plowed through the topic indexes. Not even a mention of scrape flutter. Finally, in desperation, we reached for the telephone, to call what we thought might be a good source: Ampex Corporation, Recording Products Division.

One of our subscribers, we recalled, was a design engineer there. And since Apex’s latest professional recorders were equipped with "scrape flutter filters," it seemed only natural to suppose that he might have been involved in the design work thereof. He had, and we had our answer.

It seems that, in a nutshell, there isn't a way of measuring scrape flutter. There are several ways of measuring what looks like scrape flutter, but there is not as yet any universally accepted way of measuring it, and there probably won't be until there is universal agreement about just what it is about scrape flutter that the ear reacts to. We were told, finally, that "there is some psychoacoustic data that is pertinent, but I don't think anyone has tried to apply it to the scrape flutter problem."

All of which is by way of preamble for the point we're trying to make. Why is not anyone trying to apply psychoacoustic data to the scrape flutter problem? Why, in fact, are so few people doing any research at all into the relationships between our hearing and the performance of audio reproducing equipment?

To wit: For the past five years or so, there's been an unending controversy, in print and out, between the proponents of wide-band amplifier response and the proponents of limited-band controlled-response amplifiers. Each side has stated its case, ad nauseum, to the satisfaction of absolutely nobody. The wide-banders still claim that critical listeners can hear the benefits of wide-band response, while the narrow-banders still claim that nobody can hear the difference, and that limiting the bandwidth does away with inaudible but bothersome things like subsonic rumble and distortion that lies above the highest recorded frequencies.

Why, we ask, don't they stop yak- king from the tops of their heads and do some basic research to settle the question? Assemble a panel of listeners who claim they can hear the difference between narrow and wide bandwidths, let them choose the associated equipment, so they can't argue that speakers or program sources invalidate their judgments, and then run some controlled, prolonged, tests. Nor a couple of hours of A–B tests, for these are useless for making fine distinctions. Even the best-trained ear needs at least an evening of listening, under leisurely conditions, to get sufficiently used to the overall sound to be able to analyze its subtler qualities.

To wit: Elliptical styli became all the rage when magazine reviewers (including our own) noted how much more cleanly they tracked at a given force than did spherical styli. Subsequently, it has become increasingly evident that much of their superior tracking ability is a direct result of their exerting far greater contact pressures on the groove walls, for a given tracking force. Why, we ask, doesn't somebody do some graphic comparisons, with a high-powered microscope, to show the actual relationship between stylus contact radius and tracking force? We may find that the ellipticals, despite their lower tracking force, are actually damaging our records more than the heavier-tracking sphericals. (We are ignoring for the moment the other disadvantage of the elliptical: its tendency for the high-frequency resonance to occur farther down in the audio range.)

To wit: Some of the English loudspeaker designers, and one American one (Paul Klipsch), have long contended that it was possible to hear Doppler distortion of high frequencies being radiated from a bass-driven cone. Yet the subject as a whole appears to have been ignored in the US, and in England it is the subject of endless, pointless debates like those over wide- versus narrow-band amplification in this country. Why not settle this one conclusively, with some properly conducted listening tests?

To wit: Anyone who has looked at the measured response curves for headphones and then listened to the same phones will have concluded that something is snafu’d somewhere. Typically, the measured curves look like the path of an egg beater across a pan, while the phones sound quite respectably smooth and, often, exceptionally so. Instead of publishing these curves with a philosophical shrug, why doesn't someone do some investigating to see why there is such a discrepancy, with the hope that we may end up with a set of correction curves, like the Fletcher-Munson curves, for correlating measured headphone response with subjective headphone response.

There are a few other unanswered questions we can think of off-hand. Is amplifier phase shift audible, or isn't it? Can anyone really tell the difference between a speaker system that is acoustically in-phase and one that has the woofer and tweeter 360° out of phase? How compatible are compatible stereo discs, and is there any subjective stereo loss as a result of the compatibility compromises? Is it possible, or practical, to make an electrostatic speaker system that isn't directional at high frequencies?

None of these questions can, or will, be answered by company Executives with axes to grind. They're going to require some basic research, of the kind that Bell Telephone Labs used to conduct thirty years ago. Sure, it's nice to see today's equipment designers trying to find cheaper ways of reproducing sound that's almost as good as the more expensive ways—Only a trained ear can tell the difference!—but is it really forwarding the audio art?

RCA ran some experiments back in the 1930s that proved beyond a doubt that the general public preferred low fidelity to high. They were subsequently proven to be wrong, but while no one will argue today that John Q. prefers low-fi, the same sort of thinking is reflected in the oft-cited view that the best components are so good that further improvements "would not be detectable except by the most sensitive test instruments." Let's face it: we don't know how much better the best sound reproducers could be. There's one thing we can be sure of, though, and that is that the state of the art isn't going to improve one iota until some enterprising researchers prove to the general satisfaction that audio reproduction can be better than it is now.

And who'd argue with that?—J. Gordon Holt