TAPE GUIDE (Dec. 1983)

Taping FM on Metal

Q. I use my cassette deck mostly to record FM programs. Would there be an advantage to using metal tape for such material, or would this be overkill?

-Rob Canaday, Northwood, Ohio

A. It appears that metal tape chiefly warrants its higher price when taping live material with strong transients.

Such tape is less subject to saturation by these transients than are the other types (ferric oxide, chromium dioxide, cobalt-modified, ferrichrome). But when taping FM material, which is generally subject to substantial compression or limiting that subdues the transients, the non-metal tapes appear to do a satisfactory job, leaving little room for improvement.

However, this situation may change as phono discs, FM transmission equipment and techniques, and FM tuners improve. Hence, FM broadcasts and phono discs may possess a dynamic range which challenges the capabilities of the non-metal tapes. On the other hand, technological progress continues to bring us improvements in the latter tapes, so that they may still be able to cope.

Sensitivity Adjustment

Q. My cassette deck has provisions for adjusting both the bias and record sensitivity. How are these two factors interrelated?

-Hillel Brandes, Grantsville, Md.

A. They are essentially independent of each other. The bias adjustment, which varies largely with tape type (ferric oxide, chromium dioxide and ferricobalt, ferrichrome, or metal), aims at the optimum combination of low distortion and extended treble. As bias is increased, distortion tends to decrease (up to a point), but treble response tends to drop also. Hence it may be necessary to accept a (usually slight) increase in distortion to permit adequate treble response.

The purpose of the sensitivity adjustment is to meet the requirement of Dolby noise reduction, namely that a given signal fed to the tape in recording produce a given output in playback. Accordingly, the Dolby emphasis (mostly in the treble range) provided in recording will be matched by corresponding treble de-emphasis in playback, restoring flat response. Improper matching, called mistracking, adversely affects treble response, usually causing a loss.

One Channel Missing

Q. I have owned my cassette deck for a year and a half, and the only tape I used with it was TDK SA, While I kept the tape type (bias) switch in the CrO2 position, I kept the equalizer switch in the 120-uS position, although SA tapes are supposed to be played with 70-uS equalization. Recently I bought TDK D tapes, and in playback noticed that one channel was missing. What is the problem? Did my constant use of SA tapes on the wrong equalization lead to this?

-John McHugh, Rockaway Park, N.Y.

A. No, your constant use of the same type and your use of the incorrect playback equalization could not produce the problem you describe.

Apparently, something has gone wrong in the electronic circuitry of one channel, and it will require the services of an audio shop to find the problem's cause and cure.

Old Open-Reel or New Cassette

Q. I've had an open-reel tape deck for many years and have enjoyed its trouble-free operation. Most of my recordings have been made at 3 3/4 ips; I recognized that this speed might not give the very best reproduction but afforded results decent enough for my purposes. I have begun to upgrade my audio system and would like to record more classical music from FM and phono discs. It is suggested that I get a new cassette deck, which is generally apt to be better than the old open reel decks. What is your advice?

-Steven Rannels, Philadelphia, Pa.

A. It is difficult to advise you on the desirability of buying a new cassette deck. If the old open-reel deck still works well and gives you full pleasure, perhaps you should stay with it. The decision can be made only by you.

Before deciding, visit your local audio stores and listen to their cassette decks. I realize that it is not easy to make a comparison between your open-reel deck operating in your home with a particular speaker, and a cassette deck operating in a store with, in all probability, another speaker. Perhaps you can borrow a cassette deck from a friend and try it in your home. Or perhaps you can obtain one on a trial (money-back) basis from an audio store, particularly if you are purchasing other components from that store.

Puzzling AM Noise

Q. When I record AM with Dolby NR on, although the incoming AM signal sounds clear with no noise, the signal is noisy in playback. This happens with five different cassette decks I have tried. This does not occur when recording from FM or phono.

-Robert Patterson, Des Plaines, Ill.

A. I do not have a sure answer. It may be that noise components of the AM signal, although close to or entirely inaudible, are causing the Dolby circuit to encode when recording but not to decode in playback. This would mean treble boost, and therefore noise accentuation, in recording, without corresponding treble cut in playback. Have you tried another AM source?

(Editor's Note: Also try switching in your tape deck's multiplex [MPX] filter to cut these high-frequency noise components. An equalizer could also be patched between the AM tuner and tape deck, to cut off high-frequency noise at an even lower point.)

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

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