Graphic Realism
Q. I notice that reviews of cassette decks specify the frequency response curves at -20 dB, and of course the high-end response always looks good on the graphs. But is this realistic? Everyone knows that we tape at levels typically around 0 dB, and I am sure the high-end response will then droop.
-Alfred Chiesa, Springfield, Mass.
A. It is true that when tested by a series of constant level audio signals, a cassette deck will ordinarily show treble droop if the recording level is in the vicinity of 0 dB (such droop is less with metal tape and when noise reduction is employed). However, in most music and other program material, the relative amplitude of the high frequencies is substantially lower than the amplitude of the mid-frequencies. Hence, one can usually record on cassette at 0 dB level, particularly from FM or disc, without noticing treble loss. Of course there are exceptions, particularly when recording live material with strong transients, such as guitar. But these are exceptions for most people, and in such cases one can reduce the re cording level to preserve the high frequencies, albeit at the cost of reducing the signal-to-noise ratio, too. Considering the very high S/N ratios achievable today (thanks to advanced noise-reduction systems), sacrificing a few dB of S/N usually entails little if any reduction in listening pleasure.
Tape Deck Mis-Phasing
Q. I feed a mono source into both channels of a stereo tape recorder; in playback, both outputs are combined and fed into another unit with mono input. When the playback signals are combined, the sound seems to lose its original quality and level. Even if I bring the level up, there is a loss of quality. If I disconnect either playback channel, the sound regains its original quality. Any help will be appreciated.
- Cicero LaHatte, Jr., Vicksburg, Miss.
A. There is a probability that your tape deck's output signals are some what out of phase with each other, resulting in partial cancellation. Even though there is no phase problem when the mono signal enters the deck, phase differences occur at the output owing to characteristics of the heads and perhaps to the electronic circuitry.
Conceivably, there is a gross wiring error in your deck which has changed phase of one of the channels by 180C from which it should be. This would, of course, produce gross cancellation when the outputs are combined. It seems that your best course is to use just one channel of your deck for mono recording until you can get it fixed.
Bias Percentages
Q. Why is bias measured in percent? To wit, I have seen that Type I tape requires 100% bias; Type II, 150%; Type III, 250%.
-H. P. Kornick, Sanford, Fla.
A. Type I tape (ferric oxide of the low-noise, high output type) provides a reference standard for the amount of bias required, and therefore is arbitrarily rated as requiring 100% bias The actual amount of bias current fed to the head would depend on the bias frequency, on the head construction, and on the deck maker's judgment as to the trade-off he wishes to make be tween extended treble response (requiring reduced bias) and other performance characteristics, namely low distortion and low noise (requiring more bias). If Type I tape requires a certain amount of bias current in a given deck.
Type II would require about 50% more than Type I and Type IV would require about 2 1/2 times as much as Type I.
Format Fuddlement
Q. I am going to buy a tape deck and am oscillating between cassette and open-reel units. In my opinion, one can get better reproduction at a high tape speed than at a lower speed. So, at the same price, should I buy a cassette or open-reel deck?
-George Nour, Reading, Pa.
A. There is no definite answer to your question. It depends upon your personal needs and expectations.
Owing to improvements in tape, in deck electronics, in heads, and in mechanical design and construction, a high-quality cassette deck is capable of truly high-fidelity performance: Wide and flat response extending to 15 kHz or better, low distortion, high signal-to noise ratio, low wow and flutter, and accurate speed.
In fact, those improvements have been given most prominently to cassette decks, both because cassette's slower speed (1 7/8 versus 3 3/4 to 15 ips) puts it in greater need of these benefits and because there is more demand for cassette decks. This has helped narrow the gap between the formats.
Open-reel's advantages of greater high-frequency headroom (ability to re cord high frequencies at higher levels without tape-saturation distortion) and easier editing are more significant in live recording than when taping off the air or copying phono discs. Cassette's chief advantages are low tape cost, convenient loading, compactness (especially for tape storage) and a plethora of convenience features such as automatic tape-selection programming on some decks.
Listen for yourself, to see how much difference you can hear, and how significant those differences are to you.
High-Speed Cueing and Head Wear
Q. A friend of mine refuses to use the cue feature on his cassette deck that is, he never fast-forwards the tape while the deck is in play mode. He claims that running the tape at fast speed while it's in contact with the heads will wear out the heads. If I cue my tapes a lot, am I decreasing the life of my tape heads?
-Garth Whetzel, Sharon, Pa.
A. Yes, cueing the tape past the heads at fast speed will accelerate head wear. However, depending on the type of head, it may outlast the rest of the cassette deck. This is particularly true of ferrite heads, which are claimed to have lifetimes of at least 20,000 hours and up to as much as 150,000 hours in a cassette deck at normal operating speed of 1 7/8 ips. Al lowing for a reduction owing to cueing, they should still have a very long period of serviceability. With other types of heads, there might be a problem, but probably not for a long time.
[I believe there are some decks which hold the tape a minute distance from the heads during high-speed cue, which would eliminate the problem al together. –I.B.]
(Source: Audio magazine, HERMAN BURSTEIN)
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