TAPE GUIDE (Nov. 1983)

Info on Print-Through

Q. Is it possible to get print-through on 1-mil and 1.5-mil tapes if they are played infrequently, say every six months or yearly? Does print-through occur on C-60 or C-90 cassette tapes?

-T. K. Dukes, Columbus, Ga.

A. Yes, print-through is possible in all the cases you mention. The thinner the tape (e.g. 1-mil instead of 1.5-mil or C-90 instead of C-60), the more likely audible print-through is to occur. For example, print-through tends to be about 3 dB greater on 1-mil tape than on 1.5-mil.

Print-through tends to increase logarithmically with time. To illustrate, about as much print-through occurs during days 2 to 11 of storage as occurs during day 1, and about as much occurs again during days 12 to 111. The higher your recording level, the more likely that you will get audible print-through.

The tape oxide tends to transfer its signal primarily to the next layer above it. Thus, if you leave a tape in the played condition (tail out), print through will tend to occur as a post echo, which usually is less objectionable than pre-echo-which occurs when the tape is stored in the recorded condition (head out). If you leave the tape tail out and rewind just before playing, you may accomplish something like a 6 dB reduction in apparent print-through.

Multiple Signal Processors

Q. Is it possible to connect two signal processors (such as a tape noise reduction unit and an equalizer) to one set of tape jacks in an amplifier? If yes, please explain how.

-John Chan, Long Island City, N.Y.

A. Ordinarily one can connect more than one signal processor to an audio system. These devices usually contain tape-in and tape-out jacks to replace the ones they preempt in the amplifier or receiver. Thus, two or more signal processors can often be "daisy chained" to each other. Another tactic is to introduce a signal processor, such as an equalizer, between the preamp and the power amp if these are separate units (or if the receiver or integrated amplifier separates its preamp and power amp sections, with output jacks for the former and input jacks for the latter). I cannot give you specific details for doing the above, as it may vary according to what components are employed. Consult the hookup instructions of the signal processors, and if these aren't adequate, consult your audio dealer. Perhaps you should pick your dealer on the basis of his being able to provide proper help.

Riding Gain

Q. Is it practical for an amateur home recordist to try to ride gain when making a tape from a disc?

-Philip Leak, Roseville, Cal.

A. Apparently, your intention is to vary the gain so as to maximize dynamic range, by reducing gain on low-level signals and increasing gain on high-level signals. I think that this tends to be impractical. First, you need a tape deck with excellent signal-to-noise ratio, probably at least 70 dB, in order to have a substantial margin over the dynamic range of a high-quality phono disc. Second, you must have the music well memorized, or be able to read a score before you, in order to successfully anticipate the passages that you wish to emphasize or de-emphasize. However, if you can meet both requirements, you may be able to achieve your objective.

Recording Levels

Q. Should the recording level be higher when recording from tapes or when recording from discs?

-Philip Leak, Roseville, Cal.

A. Generally speaking, recording level should be about the same when recording from tuner, phono disc, or tape. All these sources generally suppress strong transients-which could saturate the tape. However, if you have a superior source with superior dynamic range, such as a state-of-the-art phono disc, it may be desirable to back down a few dB in recording level to allow for strong transients. This is all the more advisable when recording live material that has strong transients, such as guitar or piano. Obviously, judgment and experience must be brought to bear in setting recording level so as to maximize signal-to-noise ratio without incurring noticeable distortion. Fortunately, modern noise-reduction systems (such as dbx and Dolby C) can achieve noise reduction so great that one can afford to under record a bit in order to avoid distortion yet maintain excellent S/N, Dolby Noise Reduction

Q. Using Dolby C, how much noise reduction is there in a no-signal situation and in a 148-Hz signal situation? Also, is S/N (signal-to-noise ratio) always measured at 1,000 Hz?

-Réal La Branche, Granby, Que., Canada.

A. Inasmuch as Dolby C achieves about 18 to 20 dB of noise reduction (on a weighted basis), presumably this would be the amount of noise reduction in a no-signal situation. Such NR becomes effective around 150 Hz, so that the amount of noise reduction at 148 Hz would be roughly 3 dB. Today, S/N is customarily measured on the basis of a 315-Hz signal recorded at a level that produces 3% harmonic distortion. Noise in the audio range is generally measured on a weighted basis, to reflect the ear's varying sensitivity to different frequencies; thus more weight is given to midrange frequencies than to bass and treble ones.

Changing to a Different Tape

Q. I have recorded hundreds of tapes on my open-reel deck, using Scotch 150, now phased out. I am changing to Scotch 207 and believe that the bias and equalization of my deck will have to be adjusted for the new tape. If I do this, won't it unfavorably affect the playback of my earlier hundreds of recordings?

-John Sabritt; Philadelphia, Pa.

A. No. To obtain optimum performance from the tape you now plan to use, your deck should be checked and adjusted as necessary for proper bias (at least), and desirably also for proper record equalization. The objectives should be wide, flat frequency response and suitably low distortion.

But this will not affect playback of previously recorded tapes. The adjustments outlined apply only to recording.

Playback equalization does not change; bias plays no part in playback.

(Source: Audio magazine, Nov. 1983, HERMAN BURSTEIN)

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