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Sound-On-Sound Q. Can you please tell me if one can record four separate things with a tape machine that features sound-on-sound? -Barry Edelson, Brooklyn, N.Y. A. If the tape machine truly contains provision for sound-on-sound, you can superimpose any number of recordings over each other. However, with each successive recording the noise level goes up. Hence as a practical matter about three or four sound "layers" are about the limit for high quality recording. By true sound-on-sound I mean the following: As you play a given track, say track 1, you can record the track I sound in synchronization with a fresh sound source onto a second track, namely track 3. Then as you play track 3 you can combine this with a fresh sound source onto track 1. Etc. Cross-Field Biasing Q. Limited dynamic range is one of the significant disadvantages of tape recording today. The cross-field biasing technique is claimed to improve the S/N ratio, which is a measure of dynamic range, by about 6 db. Specifications of one of the original tape recorders (Roberts) incorporating cross-field biasing indicate S/N of only 45 db in comparison with 50-54 db claimed by several medium-quality machines relying on the conventional biasing technique. If these figures mean anything, can you explain the discrepancy? -S. V. Desai, Kalamazoo, Mich. A. The discrepancy in S/N claims probably arises in the reference recording level. For home tape recorders the reference level most popularly used is one that causes about 3% harmonic distortion at 400 Hz. Sometimes, however, the reference level is one that causes about 1% harmonic distortion. The difference between the two levels is about 6 to 8 db. And this would pretty much explain the difference in the S/N figures you cite. Keep in mind that the cross-field technique, according to claims, permits a given amount of bias to be applied to the tape with less treble loss than would otherwise occur; or permits more bias to be applied than otherwise, resulting in the same treble loss but less distortion. Thus the cross-field technique permits an extension of treble, or a reduction in distortion (which in turn makes possible higher S/N), or a combination of the two. In the case of the Roberts, the manufacturer may have been going entirely for an extension of treble, with no improvement in S/N. ------ Errata Tone Burst Generator, Pt. III Figures 1, 2 and 3 were inadvertently printed up-side down. The last sentence in the caption for Fig. 7 should have referred to the d.c. zero line as being the second from the bottom. ------- Reel vs. Cassette Q. Is the pre-recorded reel-to-reel tape being phased out of production? With the advent of the cartridge and cassette machines, will the catalog of reel-to-reel prerecorded tapes dwindle, or may we lovers of pre-recorded tapes still hold out hope? -Thomas J. Schuyt, South Deerfield, Mass. A. I doubt that reel-to-reel prerecorded tape is being phased out. Though the quality difference between reel-to-reel and cassette (or cartridge) has narrowed, hopefully there are too many persons enamored of the reel for the market to evaporate. Using VU Meters Q. The following two questions have been puzzling me: (1) The VU meters in many tape recorders read the incoming signal instead of the one off the tape, and therefore read the same for all tapes. If the meters read the same for all tapes, how do you find the overload point for each type of tape? (2) Using VU meters to set initial channel balance while recording from a stereo source can be uncertain because you're never really sure that the signal from both channels is of identical volume. Is there anything that could be built or bought which would temporarily mix the signal from both channels so that a proper balance could be achieved? -John Vader, Montreal, Quebec, Canada A. (1) Recording level should be adjusted on the basis of the amount of distortion produced on the tape. Typically the VU meter is set to read 0 VU when a 400 Hz signal produces 1% harmonic distortion on the tape, as measured in playback. The recording level that results in 1% distortion varies somewhat with the brand and kind of tape. Thus the VU meter should be adjusted on the basis of the particular tape that is to be used. I should add that the meter is adjusted after the bias has been adjusted for the particular tape used. (2) Most audio amplifiers, from which you obtain the signal to be recorded, contain facilities for mixing the left and right signals, or for feeding one of these signals into both the left and right tape outputs. Cassettes and Hiss Q. How should I store my cassettes? Is print-through noticeable in cassettes; what can I do to prevent it? Is there any way to get rid of tape hiss? -Robert Simon, Flushing, N.Y. A. Store your cassettes at room temperature. Store them end up (not flat). Keep them away from electromagnetic fields, such as generated by motors, transformers, and the like. You can minimize print-through by not recording at excessively high levels and by rewinding the tape prior to playing it; also by storing it tail-out, that is, with the last part of the recording at the outside (so you have to rewind the tape prior to playing it). Tape hiss depends on quality of the tape machine and on the speed at which it operates: more audible hiss at slower speeds. Hiss also depends on the tape used, with low-noise tape giving improved results. Recording at too low a level exaggerates hiss in relative terms. (Audio magazine, Mar. 1972; Herman Burstein) = = = = |
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