HOME AND THE RANGE
Dynamics vs. Digital
The "96 dB" figure quoted for CDs is sometimes referred to as "dynamic range," but it is not: The figure refers strictly to signal-to-noise ratio. The noise floor can, indeed, be 96 dB below peak recording level. But music recorded down to -96 dB would have only 1-bit resolution.
"Technically," says Dr. J. B. Vandenbulcke of Philips, "you can get to -60 dB without significant distortion of quiet passages." That's probably a bit conservative (pun unintentional); Nimbus, a British record company, says they are already mastering with an 80 dB range, and Telarc's CDs probably have similar dynamic range.
What matters is not the S/N of the medium, but the dynamic range of the music. In the classical concert hall, Peter Burkowitz of Polygram told us, a live symphony may cover 70 dB dynamic range; very few go as high as 80, and that's just about the maximum range between the noise floor of the hall with audience (about 30 dB) and the loudest peak the audience can stand (about 110 dB).
In the home, 80 dB of dynamic range would be excessive, since the noise floor of the average home is higher, and the maximum permissible volume often lower, especially if there are neighbors, sleeping children, or people trying to make telephone calls nearby. For attentive listening, the permissible maximum range is about 45 to 60 dB.
For this reason, average recordings have a maximum range of only 40 or 50 dB (which makes them "a good match for the living room, as is," Vandenbulcke says). The LP can handle 55 to 60 dB, according to Burkowitz, so "the great advantage of CD is its lower noise floor- transparency which adds to the sensual sensation, the 'goose skin' effect, for connoisseur and average listener alike. (Vandenbulcke also points out CD's "immediate advantage in handling transients.")
That's not the whole dynamic-range story, of course. On the one hand, as Len Feldman points out, "You can handle more dynamic range than the bare numbers indicate, because the spectral distribution differs between and music." On the other, as Vandenbulcke comments, "Polygram already gets complaints: 'I have to turn the volume down.' " This is true even though CD dynamic range is limited (at least for now) by the software makers' choice, either deliberate or by default through using the same limited-range master tapes as the LP releases.
Not everyone will want compression all the time. But even if the record companies continue to restrict their dynamic range as they do now, compression will be needed sometimes--e.g., for background listening, or late at night, or when the sound system can't cleanly deliver more. Luckily, says Vandenbulcke, "CD is especially suited for compression because, with no background noise, there's no noise noise-pumping."
Going Pro
The word "professional" doesn't add as much luster to home sound gear as it did back in the days when many "home" components were public-address or broadcast equipment in wood cabinets.
Nowadays, the shoe is on the other foot.
A few years back, a friend of mine entering the studio equipment business realized the best phono preamp he could offer would be a Dynaco stereo preamp, rack mounted, with its controls preset to prevent user tinkering. He offered it at a suitable markup, but got no sales:
The specified performance was better than that of competing studio equipment, and legitimately so. But the price (while still higher than Dyna's) was so low the pros would not believe the specs. With the price raised, though, it sold quite merrily.
Today, equipment that has made its name on the home front can gain pro acceptance openly ... with a few small changes. One is to beef up the chassis, to stand the travels and travails pro sound gear is subjected to. Connectors are changed, from phono plugs to sturdier phone or XLR plugs, and inputs may be changed to balanced. The new Hafler professional amplifiers are cases in point.
Occasionally, however, there are functional changes, too. The new dbx 610, a professional version of the dbx 20/20 automatic equalizer, devotes one of its 10 memory positions to a "room curve" of the user's own devising. The system can then be equalized until its acoustic or electrical output matches this curve; the home version only equalizes towards flat response, with the user imposing his or her taste on it afterwards.
Fliers' Friend
Airline eartubes are uncomfortable and tinny-sounding. Those new, lightweight stereo headphones are neither-but you can't plug them into most airline sound systems. The answer is a $28 gadget called Airphones, from MicroFidelity in Norwalk, Conn. It plugs into the airline eartube outlets, but its plug has two built-in microphones connected by wire to a cigarette-pack-sized amplifier with two 3.5-mm stereo headphone jacks, a power switch, and a pilot light. It works best with in the-ear rather than on-the-ear phones; the former do a better job of blocking out an airliner's low-frequency ambient noise.
It's not a perfect solution, yet. It does make the airline system's frequency response more broad and even. It can't improve the airline signal-to-noise ratio or wow and flutter, both of which are often good but not infrequently horrific. And on some airline seats, big people like me find the plug sticking into their thighs.
The gain on my early sample was a bit high--I had to turn the airline's volume control all the way down to keep from blasting myself. (That's being corrected.) Also, it would have been nice to have a clip to hold the amplifier to my clothes, rather than have it lying loose in my lap. But for music-lovers who take frequent or long trips, it's the best solution to come along in a while.
Microphone Musings
There are big, impressive microphones, and tiny mikes for use where unobtrusiveness counts more than quality ... and then there are the little ones from Countryman Associates. At last October's AES Convention, I ran into two lines of tiny microphones ( 5/8 x 5/16 x 5/32 inches) from Countryman that piqued my interest. The Isomax line included the first directional lavaliers I've seen, available in cardioid, hypercardioid and figure-eight directional patterns, with frequency response of 50 Hz to 20 kHz and switchable, low-frequency roll-off and high-frequency shelf boost. You can even mount two of these mikes on a single pin or tie clip, though they'd be too close together for stereo if you want fail-safe redundancy.
Countryman's Precision Pressure Microphones have more extended frequency response (10 Hz to 25 kHz) and slightly lower noise, and appear to be omnidirectional. The spec sheets say they're so insensitive to conducted vibration that they can be placed directly on or inside an instrument (they can handle sound levels up to 150 dB).
The big news in conventionally sized microphones was made by Bruel & Kjaer, with microphones designed for studio use instead of for the instrumentation work that B & K is known for. The 4003/4006 mikes have unusually low noise (15 dB). The 4003, with power supply and transformerless, line-level output, is rated for a maximum peak sound pressure level of 154 dB; the phantom-powered 4006 has a 143 dB both 1% maximum, and reach distortion at 135 dB. The 4004/4007 mikes have about 10 dB higher noise, but can handle about 15% greater sound levels with less than 1% distortion, and about 13 dB higher levels before clipping. I heard several comments on how clean the B & K mikes sounded. I found it interesting that B & K's literature covered not only noise and frequency response, but also energy-time response and phase response, measured both on and 90° off axis.
The Box That Roared
I recently got cable TV and discovered a pleasant but unheralded feature: When a station goes off the air, my cable system keeps a carrier on the channel so viewers aren't blasted by noise as they tune past it.
That hasn't been a problem on FM for decades, since all component tuners, at least, have muting to silence vacant channels. TV sets could have that if the makers bothered--TV sound is FM, too. But so far the only TV set I've seen with it is Heathkit's old GR-2001; Heath informs me that their new GR-3000 also has it, with the addition of video muting so your eyes won't be dazzled by the snow, and a muting defeat switch on the remote controller.
Anyone else have it?
Not that all is hunky-dory on the cable front, however. My local system used to have much higher sound levels on its local-access and imported channels than on the locally broadcast stations that it carries. That seems to be less of a problem this month-but stations which are shifted to new channels on the cable (such as local UHFs) now sound abysmally distorted.
(adapted from Audio magazine, Oct. 1983)
= = = =