Tape Guide (Nov. 1980)

Warbling Saxophone

Q. I play the alto saxophone and want to make cassette recordings of it. With each one of several top-flight cassette decks, an odd fluttering or warbling tone develops. The notes come out as though burbling through water. In addition to trying different tape decks, I've tried various types of microphones and tapes, and I have even tried recording at levels so low that the tape hiss is louder than the music. Nothing helps. Any advice would be greatly appreciated.

- David Altic, Newport, Vt.

A. Your problem is a baffling one, and I don't have a sure cause or cure. Possibly your playing of the sax is somehow accompanied by a subaudible frequency that drives the record amplifier into "blocking," as some times also happens when trying to record a phono disc with substantial warp.

There are subsonic filters on the market which cut off sharply below 20 to 30 Hz. Placing one of these between the cassette deck and a preceding component such as a mixer might help. Another strategy might be to first record an open-reel tape and assuming this is successful then dub from the open-reel tape onto cassette. I have found this a worthwhile tactic when trying to make cassette recordings of severely warped records; direct recording from disc onto cassette resulted in a burbling sound similar to the one you describe.

Leveling an Organ

Q. Recently I purchased a battery/ a.c. portable cassette recorder, which I use to monitor my electronic organ. However, I find that the recorded mu sic is quite distorted. This distortion occurs at any organ output level. The recorder has auto-level control. No distortion occurs when recording mu sic at any output level from a radio or TV speaker. In each case the micro phone is placed near the speaker. Can you tell me what is causing this and if the condition can be corrected?

-M. W. Van Lenter, Clifton, N.J.

A. My guess is that when you are recording from the organ you are dealing with a much bigger and better speaker than when you are recording from radio or TV. If the organ speaker delivers powerful bass notes, perhaps even sub-audible ones, they may well be overloading your cassette machine.

If the auto-level control cannot be deactivated, I am afraid that the only suggestion I have is that you try another cassette machine, preferably one without auto-level control.

What's Digital?

Q. What specifically is digital recording? Does it mean that the recording was done on equipment equipped with digital accuracy, or does it mean something entirely different?

-Scott Barber, Douglas, Wo.

A. In conventional tape recording, the audio signal is recorded on the tape in the form of a series of bar mag nets which are an analog of the audio signal: The higher the frequency, the more bar magnets per inch of tape; the greater the amplitude, the greater the strength of these magnets.

In digital recording, the audio signal is sampled about 45,000 to 50,000 times per second, and each sample is translated into a number that shows the value of the signal voltage at a given instant. These numbers are recorded on the tape. In playback, the numbers are reconstituted into a signal voltage.

Compared with conventional (analog) tape recording, digital recording permits lower distortion and much higher S/N ratio--something like 90 dB compared with about 65 dB (at best) for conventional recording.

However, digital tape machines are still very expensive, some of them costing upwards of $100,000, so it will be a while before home digital machines are commonplace.

An important advantage of digital recording for commercial use is that it enables successive copies to be made of a master tape without loss in terms of S/N ratio. In contrast, when using conventional recording, noise increases about 3 dB with each successive copy, unless distortion is allowed to rise. Since commercial prerecorded tapes represent about a third or fourth copy of the master, the copy one buys may have 12 dB more noise than the master. However, if digital recording is employed at all stages up to and including the final one, where the digital recording is translated into a conventional prerecorded tape, this tape can have a much better S/N ratio along with low distortion.

Mating Plugs

Q. A few months ago I ordered a remote control unit for my tape recorder. When the unit arrived the male plug on the remote cable didn't match the socket in the deck, even though the plug was marked with the proper part number. The plug has only four prongs, while the socket has holes for eight prongs. What should I do?

-Les Gueydan Jr., Metairie, La.

A. The fact that the remote control plug has only four prongs, while the mating socket has eight holes, does not necessarily signify anything wrong. Four prongs are probably sufficient to perform the remote control function. If the plug and jack fit each other, the control device should work.

Magnetometers

Q. Quite some time ago I read about a company that makes a pair of magnetic devices useful to the home recordist, consisting of a magnetic field strength meter with a zero center scale. Unfortunately I cannot remember the name of the manufacturer and his address. Can you supply these?

-James Baumgartner, San Francisco, Calif.

A. Pocket-sized magnetometers, of two different degrees of sensitivity, are available from the R. B. Annis Co., 1101 No. Delaware Ave., Indianapolis, Indiana 46202.

Tape Tension and Dropouts

Q. With a Revox A-77 I am experiencing dropouts. I find the effect most disconcerting, and it ruins my listening, knowing that these dropouts will occur and waiting for them. After a while, I can't help listening less to the music and more to the dropouts--most upsetting! I have used tapes of different thicknesses, and the problem persists. An associated problem is both channels periodically fade out, as though the balance were shifting. Is this the fault of the tape or the ma chine? Can anything be done to remedy the fault?

-C.F. Gaetjens, Glenelg, South Australia

A. Your dropouts may well be due to the lack of good contact between the tape and the heads. Adjustment of tape tension is where to start. You mention that either channel appears to fade out slightly. This may relate to your dropout problem, that is, the tape may be making poorer contact with one gap than with the other--usually poorer contact with the upper (left channel) gap. The reason for this may lie in improper tape tension, incorrectly mounted tape guides, tape guides of improper width, or in other things that affect the path traveled by the tape and its contact with the heads. I'd look at these areas closely.

Bias vs. EQ Adjustments

Q. I have noticed that some of the cassette decks have only a bias adjustment switch, while others have an equalization adjustment as well. I know what each one does. What I want to know is, which one of these controls has the biggest advantage as a fine adjustment.

-John Stokes, APO 96358.

A. It might be best to begin with a review of the purpose of these switches. Some cassette decks have a single switch that adjusts both bias and equalization according to the type of tape used. Other decks have separate switches for bias and equalization. The latter design is somewhat more desirable because it offers more flexibility to those seeking flattest possible response with a particular tape.

The purpose of bias current is to re duce distortion and to increase the amount of signal recorded on the tape. Bias is applied only in recording. The purpose of equalization, which is applied both in recording and playback, is to compensate for treble and bass losses that occur in the record-play back process. The amount of bias and the amount of equalization required vary with the brand and type of tape employed.

Bias adjustment usually has the greatest effect. Relatively small changes in bias can substantially alter treble response, as well as affecting distortion. It is difficult to say that one or the other has the "biggest advantage" because both are important, and they should probably be changed together to get the most accurate fine tuning.

(Audio magazine, Nov. 1980; Herman Burstein )

= = = =