TAPE GUIDE (dec. 1984)

by HERMAN BURSTEIN

Which-Way Dubbing

Q. I own a Pioneer CT-4 cassette deck and an Aiwa AD-F330. When re cording from tape to tape, which deck should I use for recording and which for playing the tape?

-Andy Dresdner, Summit, N.J.

A. Generally, you should play the original tape on the quieter deck-that is, the one with the greater signal-to noise ratio in playback. I don't know which of your two decks is the quieter.

On the other hand, for best frequency response (including Dolby tracking, if you use Dolby NR), it may be advantageous to play the original tape on the deck that recorded it. Thus, tapes re corded on the Pioneer would be played on the Pioneer even if the Aiwa were somewhat quieter in playback (which is not to say that the Aiwa is quieter). Your best course is to experiment.

Use one deck in the playback role and the other in the record role, and then swap them, checking the results of both trials by ear. Quite possibly you will find there is no prominent difference between the roles you assign to each deck.

Bass Bumps

Q. My cassette deck has a slight but noticeable emphasis in the range of 60 to 100 Hz. For instance, when playing back a recording of a jazz group, the string bass will be slightly more pronounced on the tape than on the record from which I made the tape.

I recently acquired a speaker system that has a frequency response "hump" of about 2 or 3 dB at 60 Hz, which makes the tape deck's bass boost even more noticeable. Is there a way to eliminate this bass boost?

-Robert P. Bottman, Olympia. Wash.

A. Tape decks typically display irregularities in playback response at the low end of the audio spectrum, consisting of a series of "bumps" below about 100 Hz or so. This is due to the tendency of the entire head, rather than the gap alone, to respond to the magnetic flux emanating from the tape when the head is no longer much larger than the recorded wavelength.

Wavelengths are long at bass frequencies, with wavelength equal to tape speed divided by frequency.

However, this irregularity can be minimized by proper head shape and approach of the tape to the head.

Therefore, some decks show less irregularity than do others.

Your low-end emphasis may be due to one or more of the bumps. It may also be due to the equalization employed in recording, which sometimes supplies a mild amount of bass boost.

There is probably little that you yourself can do about this, although a qualified technician could adjust either the re cord or playback equalization; this might involve a fair amount of effort and cost.

Whether the record or playback equalization should be adjusted depends on where the fault lies. If your deck has exaggerated bass when playing standard frequency-response test tapes, then the playback is at fault and its EQ should be corrected. If the exaggerated bass is heard only from tapes made on your recorder (especially if the same problem is heard when playing those tapes on other decks), then the record equalization needs adjustment.

You might try reducing the bass in playback, either by your bass control (which may not be very satisfactory) or by a graphic equalizer (if you have one), which can usually provide quite satisfactory results.

Balancing Channels

Q. What is the best way to set the individual record-level controls so that the original source's channel balance is preserved? My open-reel deck has separate level controls for each channel, while my cassette deck has individual channel controls as well as a master level control. My preamp's stereo/mono switch does not affect the signal going to the recorder, so setting the levels on the basis of a monophonic signal is not possible.

-Brian K. Howard, Centerville, Ohio

A. This is a good question and a tough one. After all, what is the "original source's channel balance"? The relative levels of the two channels can be affected by several factors, among them the judgment of the recording engineer and the channel balance of the signal source you are using, such as a phono cartridge (output of the two channels can differ by 1 dB or more).

In general, it appears the best course is to adjust the record level of each channel independently so that pro gram peaks register at maximum permissible recording level. If necessary, then alter the relative levels of the two chancels in playback via your deck or audio system controls.

Adding Dolby HX Pro

Q. I wish to know if the Dolby HX Professional circuit can be installed in existing cassette decks.

-Steve Mably, Willowdale, Ont.. Canada

A. To install HX Pro in an existing deck would require very considerable technical know-how and skill, so that is virtually ruled out. The circuitry is sophisticated, using the high-frequency content of the program material to meet part of the bias requirement in recording. That is, as the high-frequency content increases, the bias current is correspondingly decreased because the high frequencies tend to have the same biasing effect on low frequencies as the bias current does.

Thus, over-biasing is prevented and better high-frequency response is obtained, inasmuch as treble response drops as bias increases.

Fading Highs

Q. I have a home tape deck which I use to record tapes with Dolby C NR, and I play them back without Dolby (on a car or another home player). I find that the highs fade in and out, but, when I play back with Dolby C, the fading goes away. Is this a normal occurrence, or is the cassette deck that I use for recording defective?

-Werner Apel, Lincoln Park, N.J.

A. Your deck appears to be operating normally. The Dolby NR system applies variable treble boost in recording; the lower the signal level, the more the boost. With Dolby off in playback, one might hear this variable boost as a fading effect. But when Dolby is on in playback, there is complementary vari able treble cut, which restores flat frequency response.

The amount of treble boost and cut employed by Dolby B NR is substan […]

(Source: Audio magazine, 1984, HERMAN BURSTEIN)

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