Recording TV Sound
Q. I have tried recording TV programs by using a microphone in front of the speaker, but this leaves a lot to be desired in sound quality. Is there any way I can record the TV audio by hooking the set directly to my receiver?
LUIS BOTAS Davie, Fla.
A. If your TV set uses a power transformer--and a service man can tell you this from looking at its schematic diagram--you can make an interconnection with safety.
Many TV sets have an earphone jack, and this would be the easiest point from which to feed the TV audio to your receiver's auxiliary or tape input. If there is no jack, you could simply clip the inner conductor and shield of ordinary audio interconnection cable to the TV set's speaker wires and then over to the receiver-if the TV set has a transformer.
Many-perhaps most-TV sets today do not use a power transformer, however, and in this case there is a fifty-fifty chance that the chassis of the TV set (to which one of its speaker wires will be attached) is electrically "live," meaning that it carries a 120-volt a.c. charge. The shock hazard is potentially lethal, and you risk possible damage if you try to connect it to your receiver. You can determine whether your TV chassis is "hot" by using an inexpensive (under $1) neon tester, available at any hardware or electrical store.
You connect one end of the neon tester to a known electrical ground (a cold water pipe will do) and touch the other lead of the tester directly to the metal TV chassis. If the bulb glows, the chassis is "hot." Reverse the plug from the TV set to the wall outlet and try again. If the lamp lights in either position you have a "hot" chassis. Only when a TV chassis is known to be electrically isolated from the a.c. line is it safe to connect it to a system.
(Sorry, we have not tested any of the commercial TV sound adapters.) Whether all this is worth the effort is a debatable question. All of us have been conditioned to expect a certain kind of sound from the modest, unsophisticated speakers used in TV sets. But played through a hi-fi system, the full horror of the original TV sound be comes apparent. In listening to a TV concert, for example, the volume compression that passes as "normal" through the TV speaker becomes very disturbing-to say nothing of the very high hum levels you didn't hear be fore because the TV speaker couldn't re produce the relatively low frequency.
Mixing High Frequencies
Recently I tried playing some of my Q stereo tapes in mono mode and was surprised to find that all the high frequencies seemed to disappear. The tapes sound fine in stereo. Is there some connection between stereo and high-frequency response?
TREVOR BRYANT, Cambridge, Mass.
A. The problem you've encountered has nothing to do with stereo or mono per se, but indicates that you have a tape head that is out of adjustment (or defective). If the problem occurs only with tapes you have recorded yourself and not with prerecorded tapes, the record head is at fault; if you experience it with all tapes, the trouble is in the playback head.
The difficulty arises because the two head gaps are not perfectly aligned with each other.
This introduces phase differences between channels, and these are most pronounced at the high frequencies. In stereo these phase differences may pass unnoticed, but when the two signals are added together, one may can cel out the other, leading to the treble loss.
Rewind Tension
Q. When I rewind a tape on my reel-to-reel machine, the tape is always very tight. Will this cause a loss of the signal? The fast-forward mode doesn't have this problem.
CALVIN OLSEN; Fair Oaks, Calif.
A. An excessively tight rewind won't cause a loss of the signal itself, but it can lead to physical deformation of the tape, which will show up primarily as an apparent high-frequency loss. If the edge of the tape becomes deformed, the head gap can't remain perfectly perpendicular to it, since the tape no longer has a true edge. The loss of perpendicularity ("azimuth error") will result in deficient treble. Tight winding may also cause--or aggravate--problems with print-through, which is the tendency of a "loud," heavily magnetized section to transfer itself to an adjacent layer where it is heard as a faint pre-echo or post-echo.
While the change from acetate to polyester backing materials has lessened the problem of expansion and contraction of tape during seasonal (temperature/humidity) changes, tape should certainly not be stored for any length of time in too tightly wound a condition.
Professionals all advise that tapes be stored in a "played" rather than a "rewound" (or "fast-forward-wound") condition, and that advice goes double if you suspect excessive winding tightness. I suspect it on your ma chine; the fact that you can notice a difference in tightness between the two high-speed directional windings is an indication of trouble.
Excessive holdback tension (caused by a too-tight brake, for example) will cause a tight re wind and should be fixed.
Dolby: Better Off?
Q. I record cassettes with the Dolby switch on. On playback, if I switch the Dolby circuits off, the higher frequencies are much more apparent-the whole recording sounds clearer and better. Why?
DEBORAH KEYES, New York, N.Y.
A. During recording (the "encode" cycle), the Dolby system picks out those high frequencies that are low in level and deliberately boosts them up in amounts that vary, but which may be as much as 11 dB. If, during playback, you do not "decode" the tape, you lose the benefit of the noise reduction, of course, but you get instead a somewhat "brighter" sound in which the originally soft high frequencies have been accentuated. This lends a somewhat crisp, articulated character to the sound that quite a few people besides yourself find preferable to objectively "flat" frequency response. (And, if the combination of your machine and the tape being used does not provide flat response to begin with, you may have good reason to prefer the non-decoded playback.) High-level ("loud") treble sounds are not affected by the Dolby system in either the en code or decode modes, but in cassette recording and in normal FM broadcasting they are subject to an overall treble boost (equalization) that often exceeds the capacity of the tape or the maximum permissible broadcast modulation on FM. When such excesses occur, the result is-at the very least--a loss of treble material that, musically speaking, ought to be there. The exaggerated brightness of a non-decoded Dolbyized tape or broadcast might help the ear to overlook this loss.
Equivalent Tapes?
Q. Is there an easy-to-read interchangeability chart accepted by tape manufacturers that provides straightforward information on the comparative quality of one "model," "brand," or "type" of tape with another? How can you tell which kinds are really the same?
KELLY HUNT, El Paso, Texas
A. Yes, there are such charts-one per manufacturer, and usually jealously guarded to ensure secrecy! And there are great similarities among a number of brands of tape because most manufacturers do not make their own oxide particles, but buy them instead from big chemical companies such as Pfizer and Hercules Powder.
Even if I were able to give you a partial customer list for Pfizer's very popular No. 2228 (known affectionately in the trade as "two cubed eight") particle, however, you could get only approximate equivalencies, for ultimate performance depends on the individual manufacturer's binder formulation and coating procedures. And, at the "leading edge" of tape technology there are particle developments in the works that remain-for a time, at least-exclusive to the individual companies that are working on them.
So the best you can do, unfortunately, is to be guided by the periodic test reports on tape that appear in this and other magazines, on the groupings of "recommended tapes" the recorder manufacturers provide, and ultimately on your own experience of what works best for your machine.
Oral History
Q. I am planning to make oral history recordings to be used for libraries and schools (after editing and duplication). The originals will be recorded in the home of the subject-usually an old-timer. Would you recommend that I use a cassette or reel.
VAN ESSAYAN; Monterey, Calif.
A. My suggestion would be to make the original recordings on a high-quality cassette machine equipped with an automatic recording-level control. When you go into the home of an elderly person to interview him on tape, you want your unfamiliar and possibly intimidating paraphernalia to be as inconspicuous as possible. Of course, the subject knows he's being recorded, but you should prevent him from being distracted by your fumbling with record-level controls or by the sight of reels hypnotically spinning around and-wasting" tape while he struggles to re call something. For best-quality results, you should select a machine that is a.c. operated (to maintain good speed stability) and mechanically quiet (so it can be reasonably near your microphone without its sound being picked up). Don't put microphone and ma chine on the same coffee table, or you'll pick up a lot of rumble.
For editing purposes, you'll want to dub the original cassettes onto an open-reel machine, preferably half-track (full-track if you've re corded in mono and have such a machine), preferably at 15 or at least 7 1/2 ips. This transfer should entail little if any audible loss, and it can easily be edited into a first-class master.
Whether you then use the spliced-up open-reel tape or a one-to-one copy of it as your duplicating master depends simply on the number of copies you will require. (See "Noise Reducers" in the October issue for devices that may be helpful to you in the duplicating process.)
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Also see:
A BEGINNER'S GUIDE TO HI-FI---Selecting equipment intelligently is something anyone can do ROBERT N. GREENE
AUDIO NEWS: Audivideo, Russian RFI , and Quadcasting, LARRY KLEIN, RALPH HODGES, CHARLES REPKA
Technical Talk, Julian D. Hirsch
I Remember Mono--An Audiobiography
Source: Stereo Review (USA magazine)