Tape Guide (May 1979)

Quality Taping

Q. Could you tell me some of the factors that go into a quiet tape recording?

- Victor Joutain; San Francisco, Cal.

A. Quiet tape recording depends upon, at least, the following factors:

1) Use of a good quality, low-noise tape.

2) Application of as much audio signal as the tape can accept without running into noticeable distortion; different brands and types of tapes differ somewhat in this respect.

3) A properly calibrated meter of good quality to indicate recording level enabling the recordist to apply sufficient signal to the tape so as to get a high signal-to- noise ratio, yet without running into excessive distortion; a peak-reading meter or other peak-indicating device (such as an LED) can be more helpful than an average-reading meter.

4) A tape deck with well-designed and well-constructed record and playback amplifiers producing minimum noise; this includes a well-designed bias oscillator that produces a waveform with minimum distortion.

5) A tape deck with separate record and playback heads, so that the playback head can be specifically designed to produce a high-level signal.

6) Inclusion of a noise reduction unit, either as part of the tape deck or as an external adjunct.

7) Operation of the tape deck at a relatively high speed as the signal to-noise ratio tends to improve as speed goes up.

8) Use of wider tracks, since half-track recording puts more signal on the tape than does quarter-track recording, so the S/N ratio tends to be about 3 dB higher for half-track.

9) When recording from a micro phone, use a microphone with a relatively high output, and use the proper cable to minimize noise pickup. 10) When recording from FM or phono discs, use of audio equipment with minimum noise.

Distortion Dilemma

Q. I am encountering a problem in attempting to dub tapes from my open-reel deck onto my cassette deck via my receiver. I get an unusual amount of distortion and excessive volume. I encounter no similar problems when recording from a micro phone. My suspicions lead me to believe that the problem lies in the type of patch cord I'm using. Can you advise me?

-Charles Spencer, Blackwood, N.J.

A. The fact that you are getting excessive volume along with distortion suggests that you are recording at too high a level. Try recording at a lower level, preferably by reducing the play back output level on your open-reel deck. If you suspect that a patch cord is at fault (a near-short could cause the sound to seem distorted), substitute another cord. By any chance are you feeding the recording signal into the wrong input jack of your cassette deck, that is, into a low-level (microphone) instead of a high-level jack? This could have the same effect.

VU Differences

Q. I've heard that different manufacturers calibrate their VU meters differently so that the optimum recording level may be other than 0 VU. Could you expound upon this?

- Anton Verhulst; Everett, Mass.

A. Makers of high quality tape decks generally calibrate the VU meter to read 0 VU at a signal level which, at a frequency in the range of 400 to 1000 Hz, produces about 1 percent harmonic distortion on the tape. This allows about 6 to 8 dB "headroom" to compensate for the fact that the meter cannot follow sharp transients and, therefore, tends to understate the re cording level on peaks of brief duration. A signal level about 6 to 8 dB above 0 VU causes about 3 percent distortion, about the maximum consistent with good recording quality.

Meter Purpose

Q. How do you read a VU meter, and what is its purpose besides monitoring the volume level in recording?

-J.J., Alhambra, Cal.

A. Assuming that your deck has a true VU meter (which reads average level rather than peak level), one adjusts the gain control in recording so that the meter doesn't go above 0 VU.

However, some audio material has very sharp transients which the meter cannot adequately follow. Then the recording level should be set so that the pointer doesn't exceed some figure below 0 VU, e.g. -5 VU. Just how much below is a matter of judgment on the recordist's part. He should aim to set the recording level low enough to avoid excessive distortion, but high enough to get a good signal-to-noise ratio. Experience, plus trial and error, will assist his judgment.

In some tape decks, the VU meter is used, through a switching arrangement, to indicate the bias level.

In playback, the meter may be used to indicate the level of signal going to the equipment thereby avoiding the possibility of either overload or of in sufficient signal. Also, the VU meter may be more convenient than an external meter to indicate playback level when adjusting equalization and/or bias to achieve flat response. See "Reading VU Meters," Audio, Sept., 1976, p. 42.

Taping Interference

Q. When recording an FM broadcast a burst of static is audible through the monitors as well as on the tape play back. All interference stops when the tape deck is off, also, no interference occurs when recording through the phono circuit of my receiver. What could be wrong?

- Patrick Grealy, Stratford, Conn.

A. The problem seems to be interference between the 19-kHz pilot signal of stereo broadcasts and the tape oscillator frequency, or between the tuner's oscillator and the tape machine's oscillator. If the latter is the cause, then moving the tuner and tape deck further apart might help. If the former is the cause, you need a 19-kHz filter at the output of your tuner, or at the input of your tape deck. Inquire at your local audio store about a suitable filter.

(Source: Audio magazine, May 1979; Herman Burstein )

= = = =