May 2002   

The World Above 20kHz:
What Are We Missing?

by PAUL D. LEHRMAN

Like most of us, when I was a kid, I suffered from a bad case of technolust. Among my favorite reading matter were catalogs from Allied Radio, the monthly Popular Electronics, and the publications of the American Radio Relay League, the organization of ham radio operators, of which I was a member—although at the age of nine, a not-very-accomplished one. One of my favorite books of theirs was a slight volume called "The World Above 50 MHz," which talked in vague terms how the hams of the future might be able to take advantage of what were then considered "trash" radio frequencies. Although these high frequencies (or very short wavelengths, as we used to refer to them) might be usable for things like commercial television and FM radio broadcasts, they were not much good for any sort of long-distance communication, which is what hams lived for. Novice ham operators (like me) were allowed to operate voice transmitters way up there around 144 MHz, where they wouldn’t bother anyone. Much more valuable to experienced hams was the spectrum between 2 MHz and 30 MHz, since signals at those "shortwave" frequencies could bounce off the ionosphere and travel around the world. Above 50 MHz was of interest only to "experimenters."

Since those days, the VHF, UHF, SHF, and EHF ("S" for Super and "E" for Extra, in case you were wondering) bands have, of course, been used for a stunning variety of purposes, and are now being viciously fought over by a plethora of different wireless services, both real and imagined. With the advent of the communications satellite, shortwave radio went more or less the way of the dinosaur. Congested spectra made signals that did not bounce, but instead beamed right through the ionosphere, much more valuable.

Today we all talk nonchalantly about 700-MHz digital television broadcasts, 900-MHz wireless phones, 1.9 GHz digital cellphones, and Ku-band satellites, which use the 13-18 GHz band. In Europe, research and field testing is going on into frequencies as high as 60 GHz—which would have a great future in point-to-point transmissions, were it not that they tend to be disrupted by things like snow.

But you don’t want to hear me talk about radio, you want me to talk (if at all) about audio. Just as the radio amateurs of yore considered 50 MHz the top of the usable spectrum, audio engineers and enthusiasts have long regarded the 20-kHz upper limit of human hearing as an inviolate parameter, and signals above that simply didn’t need to be dealt with. In the days of analog, this proved to be very helpful since the physics of audio transducers and media—the tape and tape heads, microphones, and speakers—made recording ultrasonic frequencies a difficult proposition indeed: above about 10 kHz, for every tiny increase in high-frequency response, there was an enormous increase in cost.

The rest of this column, along with 56 more, is now available in The Insider Audio Bathroom Reader, published by Thomson Course Technology PTR.

Copyright ©2006 by Paul D. Lehrman