by Craig Stark
Pitch Problem
Q. My three cassette decks all run at slightly different speeds, causing horrendous pitch problems in editing home recordings. This also raises a question about buying commercially recorded cassettes-who wants to listen to a symphony a quarter-tone sharp or flat? Can anything be done about this?
ROBERT E. NEIL; Oberlin, Ohio
A. If you're heavily into tape editing, I marvel at the fact that you're using cassettes rather than open-reel, but even if you changed formats you would still be subject to some pitch shifts when interspersing sections made on one machine with those made on another. Absolute speed errors always exist to some degree, and one reason why professional decks use such apparently "over-built" motor and drive systems and complex servo-controlled reel-tensioning devices is to minimize audible pitch changes when joining a "take" from the middle of the reel to one recorded near either end, even on the same machine.
There are a couple of things you can do, however. Many tape decks (both open-reel and cassette) are direct-driven by quartz-crystal phase-locked-loop servo systems, and these offer the highest potential for realizing near-perfect speed accuracy.
Some of these (as well as a number of decks that are not quartz-referenced) are also equipped with a pitch control capable of varying the drive speed by about a semi tone-surely enough to compensate for nor mal deck-to-deck differences. These pitch controls override the quartz reference (if any) and normally operate only in the playback mode.
If you don't want to change decks at this point, however, you still may get lucky.
Most good cassette decks today use some kind of servo-controlled drive motor(s), and it is often possible to "tune" the reference frequency of the servo system over a slight range. With the aid of a schematic diagram, a wow-and-flutter test tape containing a sustained 3,000-Hz (or 3,150-Hz) test tone, and a digital frequency counter, a technician can adjust the speed differences between your three decks so that all will play back the test tape at the same frequency. This may involve changing a fixed resistor to a small adjustable one on one or more of your decks, but that's no big deal.
You increase the odds of success if you have the technician use the middle section of the test tape (approximately the same amount of tape on each reel) for the adjustments.
The above will minimize the possibility of audible pitch shifts in editing, but you must realize that when two pieces of tape are edited together between notes the ear is much more likely to detect a pitch change than when it is dealing with sections where there are even a few seconds of silence in between. Sensitivity to small changes in pitch varies markedly between individuals (as does the related sensitivity to wow and flutter), which brings me to the point you raise about listening to prerecorded cassettes. Relatively few people-specifically, those endowed (or cursed!) with "absolute pitch"-would know, offhand, whether a recording of a symphony was a quarter-tone sharp or flat, much less whether the conductor had tuned to A = 440 Hz or A =443 Hz. If you're one of them, a deck with adjustable playback pitch control is, for you, a musical essential.
Tape Contact
With several of my cassettes that haven’t been played for some time. I find that the treble--and sometimes the whole signal--is missing until I press my deck's play lever down extra hard and hold it there. Then the playback is okay. Can this nuisance be fixed?
MICHAEL SZIGETY; Madison, N.J.
A. If you try to visualize what happens when you press the play lever on your deck, it may help you understand where the problem(s) may be. When you press the lever three things occur: the reel brakes are released, the pinch-roller presses the tape against the rotating capstan while drive is applied to the take-up reel, and the head assembly is pushed into the cutouts in the front of the cassette shell so the moving tape will wrap itself firmly against the curved head faces. Your problem is clearly in this last function: insufficient contact between tape and heads is causing treble loss or worse.
Any mechanical latching mechanism such as your play lever-must accommodate a slight amount of "over-travel" to ensure that the latch will catch reliably. In other words, it permits you to push slightly farther than should be necessary in order to ensure reliable tape/head contact. When you push down (and hold) extra hard to make these cassettes playable, you're working with this built-in "over-travel" margin, pressing the head assembly just a little further into the cassette openings.
It's possible, then, that the head-shifting mechanism is "latching in" at a marginally adequate position, pushing the tape just barely enough so that the spring-loaded pressure pad behind it creates adequate tape/head pressure on new (or some brands of) cassettes but not enough to deal with these particular older (or other brands of) cassettes. There are, in other words, two possible sources for the problem: (1) the time elapsed since last playing (the tape may have become a little sticky or the pressure-pad spring may have relaxed a little); and (2) cassette-brand/deck incompatibility, your head assembly being so set that it doesn't intrude into the shell openings quite far enough to make firm contact with this manufacturer's cassettes.
As a quick check: (a) run the trouble some cassettes back and forth a couple of times on high-speed wind; (b) rap the front edge of the cassette firmly against a desk a couple of times, but not as hard as if you were trying to crack an eggshell; (c) try playing again. If this works, fine. If it doesn't, listen carefully to a recording you make on the same kind of cassette: you may have a simple brand incompatibility. If you have problems with more than one name brand, a technician should adjust the head assembly.
What, No Bias?
Looking through a recent audio directory, I noticed that while many cassette decks had a variable-bias feature listed, none of the open-reel decks did.
What kind of cavalier thinking is it for manufacturers to include such an advanced feature on cassettes and to omit it from open-reel products whose owners are far more likely to want to use it?
E A. MULVANEY; Los Angeles, Calif.
A. To paraphrase the Bard, the fault, dear reader, is not in our decks, but in our directories, which are (sometimes) inadequate. There are plenty of open-reel decks with front-panel bias adjustments, but this particular directory's inquiry form to be filled out by the manufacturer simply omitted that category. Next time, look in the store as well as the book.
Also see:
MICROPHONING: The two big microphone questions are Where and How Many?
Source: Stereo Review (USA magazine)