TAPE GUIDE (Apr. 1990)

Type I EQ for Type II Tape

Q. A number of prerecorded tapes I own claim to use chrome tape, which is Type II, but require 120-µS playback equalization, which is Type I. Is this correct? What advantage is there in using Type I equalization with Type II tape?

-Chris Kim, Plano, Tex.

A To the record company, the advantage is compatibility with older or lower cost players that have only this equalization. In home recording, the question is a bit more complex.

It is usually quite feasible to use Type I (120-uS) equalization with Type II tape. Use of 120-uS rather than 70uS (Type II) playback equalization signifies less treble drop (converse of bass boost) in playback, and correspondingly less treble boost in recording. (The reasons for this are rather technical; see my article, "The Whys and Hows of Cassette Equalization," in the June 1985 Audio.) With less treble boost in recording, there is less danger of overloading the tape at high recording levels; hence there is less danger of distortion and treble loss-in other words, more recording headroom.

Type II tape is generally capable of more extended treble response in recording than Type I. Therefore, in playback one can use an equalization characteristic with more treble drop yet maintain treble response satisfactorily.

This greater treble drop in playback produces an improvement in S/N of about 4.5 dB. However, in these days of very high S/N ratios, it is quite practical to forge an improvement in S/N of some 4 or 5 dB without appreciable effect on listening pleasure in most circumstances. That is, one may use 120-µS equalization with Type II tape, instead of 70 µS, and thereby gain more headroom in recording.

So ... if your prerecorded cassette says to use 120-µS playback equalization, do so. If, instead, you use 70 µS, you will experience some treble loss, which may or may not bother you--or it might even be pleasing. Always experiment with options. Settle for that which sounds best, not that which is merely technically correct.

Poor Erasure

Q. My cassette deck allows user adjustments of bias and record level via a test signal. After making these adjustments, I record right over the test signal. Recently, I recorded a CD and, in playback, heard the test signal on the recording. What could have happened?

-Name withheld

A. It appears that the erase head is not operating properly. This could be the result of a defect in the head (such as a partial short circuit), insufficient oscillator current reaching the head, dirt on the erase head, or other factors preventing close contact between tape and head.

(Audio magazine, Apr. 1990, HERMAN BURSTEIN)

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