Choosing the Right
Tape
Although most people have cassette decks these days, very
few of those perform as well as they should. When the cassette format was introduced
almost forty years ago, the intention was that all machines and all tapes be compatible
with one another. In most ways that was achieved: all cassettes are the same shape and
size, the tape moves at a standard speed, and so forth. But the magnetic properties of the
tapes vary widely, which makes matching tape and recorder a tricky process. Yet even a
slight incompatibility will result in degradation of sound quality.
The most critical aspect of tape recording is something
called "bias." As it happens, the only way the system can even approach true
high fidelity is if a high-frequency bias signal is added to the conventional audio before
it is recorded on the tape. This is typically many times the highest frequency contained
in the music itself and so is inaudible, but without it the distortion levels would be
unbearable.
Adding the extra signal is no big deal in itself; the
difficulty is in knowing how much to add. A tiny bit too much, and the sound will be
significantly duller than it should be; too little and the sound will become shrill. The
proper amount is determined by the properties of a particular tape formulation, and
unfortunately they are all different. Not only are there significant variations from one
brand to the next, even with tapes of the same nominal class, but tapes from the same
manufacturer can have widely differing bias requirements. There have even been instances
when what appears to be exactly the same tape shows such differences; manufacturers
occasionally upgrade their products without trumpeting the fact on the packaging, and that
can affect bias.
The first step in achieving a proper match is to make sure
your cassette deck is set for the proper tape type, as the three currently in use require
very different bias levels. The lowest is Type I: ferric oxide or "normal,"
which covers most drugstore-grade tapes and virtually all commercially recorded cassettes.
More advanced is Type II, also called high bias or chromium dioxide. Top grade is pure
metal Type IV (there was once a Type III as well, but it no longer exists).
Older decks have switches that must be set manually for
each tape type, while many newer models set the overall bias automatically by sensing
cutouts in the cassette shell (some older tapes don't have the cutouts, so they may not
operate properly in modern recorders).
Simply putting the bias switch in the correct position
doesn't necessarily assure you of a correct match, however, as the settings are only
approximations. Individual tapes can vary widely, so a certain amount of experimentation
will probably be required to get an exact match. Look first in the recorder's manual to
see whether the manufacturer has set the machine up for a specific tape. If so, buy that
and use it.
If the manual lists many tapes from different tape
companies, you can be sure that they won't all work equally well. It's worth the time and
money, therefore, to invest in some of the tapes listed and try them out to find the one
that works best. This can be done easily by ear: simply record a piece of music --
preferably one with lots of treble, as that is what is most likely to be affected by a
mismatch -- and play it back, switching back and forth between the recording and the
original. The tape that sounds closest is the one to use. If yours is a three-head machine
that allows you to monitor off-tape as you record, the process is that much easier: you
just have to switch between monitor and source as you record. If you can't make up your
mind between two or more tapes, try repeating the test with a recording of the
interstation noise from your FM tuner. It's very good at revealing tiny differences.
A few machines provide a fine bias adjustement that lets
you match the recorder to any tape you choose. Follow the instructions, and set the
machine up every time you change tape brands. The improvement in sound quality will
definitely be worth the effort.
And if all else fails, you can take your recorder to a
service facility and have it professionally matched to whatever tape you want to use,
although few recorder owners have to go to such lengths.
...Ian G. Masters
ian@mastersonaudio.com
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