Tape Guide (Q and A) (Sept. 1975)

Comparing Specs

Q. Recorder A has the following specifications: frequency response 20-20 kHz, wow and flutter .09%, signal-to-noise ratio 52 dB. Recorder B has specifications of: frequency response 50-15 kHz, wow and flutter less than .15%, signal-to-noise ratio 55 dB. Recorder B sounds better than A. Why? Is a full-track head better than a quarter-track head?

-Dean Frazier, Huntsville, Ala.

A. Recorder B should sound better because (1) it has flatter frequency response (although a more limited range) and (2) it has a better signal-to-noise ratio. Many tape machines that boast of response down to 20 Hz and up to 20,000 Hz fail to keep response flat within 1 dB or so throughout this range. To achieve response out to 20,000 Hz, they may sacrifice performance in terms of noise and/or distortion. They may also have a treble peak in an audible part of the audio spectrum. To achieve response down to 20 Hz, they may make similar sacrifices.

A full-track head has the advantage of higher signal-to-noise ratio since it picks up more information from the tape than do halt-track and quarter-track heads. Also, the full track head permits tape flaws, such as dropouts, to average out better (that is, to be less noticeable). On the other hand, a full-track head has the disadvantage that a given amount of azimuth misalignment results in more severe treble loss.

Limiting and "Unlimiting"

Q. Can program material which has been processed through a limiting amplifier (limiter) be restored to its original dynamic range?

- Andrew Butler, Victoria, B.C., Canada

A. A limiter or clipper completely removes dynamic changes above a particular signal level, no matter how large a signal is fed into it. A complementary "unlimiter" would have to detect how much dynamic range had been lost. This is obviously impossible if the limiter has done its job perfectly. A compressor, on the other hand, only narrows the dynamic range of the program material, but does not cut it off, as a limiter or clipper does. Thus, programs which have been compressed may be processed back to their original dynamic range by an expander, if the expander is set to complement the action of the compressor.

Taping Phono Discs

Q. I have questions about taping new phono records. It seems that, depending on the manufacturer, recording levels on channels A and B vary 4 to 5 db from each other. This is more obvious with popular music than with classical records. Is this situation common? Also, when taping records, should both channels be adjusted to the same level as indicated on the VU meters?

-Ted E. Hayen, Lawton, Oklahoma

A. To the extent that each channel on a stereo record has different frequency content, one may expect some variation in sound level between channels. In the processing of the master tape and subsequent tapes until the sound gets onto the records, there may be unbalance resulting in different levels on the record even for the same sound. Something like 2 or 3 db may be expected. But 4 to 5 db differences are a bit high. On the other hand, rock records are not always made with as much care as are classical records. Too, it's possible that the difference is not entirely on the record, but partly in the calibration of your VU meters.

In recording a tape from a record, adjust separately the recording gain control for each channel on the basis of the VU meter indication. This may result in different settings for the two gain controls. It is assumed that the two VU meters are identically calibrated, so that a given sound level produces the same indication on each.

(adapted from Audio magazine, Sept. 1975; Herman Burstein)

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