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The Source of Pre-Echo
Q. I recently added some high-quality prerecorded cassettes to my collection. Although I am pleased with their overall performance, I detect some pre-echo before some of the se lections. If these tapes are dubbed directly from the master tape, as claimed, how does one explain this?
-Mark Metzger, Woodstock, N.Y.
A. The pre-echo you hear-a form of print-through-may have been on the master tapes, or it may have been picked up by your tapes after they were dubbed from the masters.
Print-through is more likely to occur when a tape is recorded at a high level and is more severe when a recorded tape is stored under conditions of high temperature or subjected to a slight magnetic field. Most of it occurs during the first few days of storage. To some extent, print-through can be reduced by putting the tape through fast wind and rewind just prior to playback.
Pre-echo occurs when the tape is stored head out-that is, with the be ginning of the tape at the outside of the reel. Post-echo occurs when the tape is stored tail out, with the end of the tape at the outside. Because post-echo is generally less offensive than pre-echo, professional master tapes (which are recorded only in one direction) are usually stored tail out. This technique won't help much with home tapes, which are recorded in both directions; no matter how they're stored, print-through will show up as pre-echo in one direction of play and post-echo in the other. If the print-through on your tapes occurred after they were dubbed, they will exhibit this phenomenon; if the print-through takes the form of pre-echo for both tape directions, then the master tape was probably at fault.
Home Taping for the Car
Q. I have a compact system (including AM/FM receiver, cassette deck, eight-track deck, and turntable). I use it to record cassettes for playback in my automobile. What is the best brand and type of tape to use?
-Arthur Goldklang, Wantagh, N.Y.
A. My guess is that the cassette deck in your compact system is intended for ferric-oxide (Type I, normal-bias) tape, inasmuch as you do not mention its having a switch that adjusts equalization and bias for different types of tape. However, if it does have such a switch, you may get good results with either Type I or II (chromium dioxide or ferri-cobalt, high-bias). Try both types and judge with your own ears which gives better results. If you hear no significant difference, you might as well use whichever type costs less.
In playback on your car's deck, the equalization switch should ordinarily be set to 120 µS for ferric-oxide tape and to 70 uS for any other types. How ever, there is no harm in experimenting with "wrong" settings, which some times provide more pleasure to the ear.
Of course, you should limit your choice of tape to brands of good reputation. The policy of Audio prohibits me from recommending specific brands.
Clarifying Noise Reduction
Q. Why would one want to use Dolby or dbx NR when recording Compact Discs onto tape? I realize that these NR systems help eliminate noise that occurs while taping a phono re cord, but are they still necessary when recording a nearly noiseless CD?
-Paul C. Lessard, Davis, Calif.
A. An NR system such as Dolby or dbx reduces noise produced by the tape recording and playback system.
It cannot reduce noise already present in the signal source that is fed to the tape deck. Basically, the Dolby and dbx NR systems compress all or part of the signal in recording and expand it in playback. The downward expansion in playback not only reduces the signal level but also the noise produced by the tape system.
Tape system noise is produced by the record and playback amplifiers, by distortion in the oscillator waveform used for recording bias and erasure, by irregularities in the motion of the tape across the heads, and by irregularities in the tape's magnetic coating.
A good cassette deck can typically achieve a signal-to-noise ratio of about 50 to 60 dB without NR. With Dolby B it typically achieves 60 to 70 dB; with Dolby C, from 70 to 80 dB, and with dbx, 80 dB or more. Hence NR is important in preserving CDs' dynamic range and S/N when taping from them.
However, inasmuch as the dynamic range of music seldom exceeds 70 dB and is often substantially less, any NR system which ensures an S/N of 70 dB may be considered quite effective.
Dubbing and Decoding
Q. My present two-head cassette deck has Dolby B and C and dbx noise reduction. I am planning to buy a three-head deck with the same three NR systems plus HX Pro. Can I dub satisfactorily from one deck to the other, or should I get another three-head deck? When dubbing tapes made on the three-head deck, is it better to dub from that deck to the two-head ma chine, or should I play those tapes on the two-head deck and use the three-head deck for recording? Also, can I dub from a three-head deck using dbx NR to a two-head deck using Dolby B or C NR?
-Tyrone Thompson, Baltimore, Md.
A. Theoretically, one will be best off playing a tape on a three-head deck because its separate playback head can have a narrower gap and therefore yield better high-frequency response.
On the other hand, usually it is best to play tapes on the same deck that was used for recording them. This tends to minimize problems of azimuth mis alignment and (if you are using Dolby NR instead of dbx) Dolby tracking.
However, the ultimate answer is obtained only by trying the dubbing pro cess in the various possible ways.
You shouldn't have any problems if you want to play a dbx-encoded tape with a deck that provides dbx decoding and then record with a deck that provides Dolby encoding.
Q. Recently I bought a major manufacturer's cleaning kit for my cassette deck. The kit has two different solutions, one for the tape heads and the other for the pinch roller. During the cleaning process, I accidentally used the pinch-roller solution on the heads. I am worried that this may have dam aged the heads and might cause distortion or other problems in playback.
Also, how do I know whether the heads are in good condition?
-Jim Tang, San Francisco, Calif.
A. I am inclined to doubt that the roller-cleaning solution would harm the heads. It is to be expected that some users might get into this mixup, and I believe that a reputable maker of such kits would take appropriate precautions. Cleaning the heads again with the proper solution is probably all that is necessary. Of course, I can't be sure. The best answer has to come from the manufacturer of the kit; you might write to them. If your deck sounds the same as before the mixup, it is unlikely that harm has been done.
As for judging the condition of the playback or record-playback head, one can tell when a head is unduly worn by its failure to reproduce the highest frequencies-that is, when the sound is dulled in playback. A good test is to record and play interstation FM noise and compare the tape play back with the source. However, dulling of the sound could also be due to improper (excessive) bias. In the case of a deck with separate record and play back heads, azimuth misalignment could also be responsible.
Q. I went into a pawn shop the other day to see what they had in stereo equipment. I saw a cassette deck, the Project/One FLD 7000, which I had never seen or heard of before, and I have been an audiophile since 1960. It was the most impressive and good looking deck that I have seen, with quality written all over it. It seemed at least eight years old, weighed at least 20 pounds, and appeared in excellent condition. I would appreciate any information you can give me about who made it, in what year, and its approximate price.
-Guido Stabile, Boynton Beach, Fla.
A. I'm sorry, but no one at Audio has heard of this deck. Perhaps some reader can enlighten us.
If you are thinking of buying it, in principle I am opposed to purchasing a deck some eight years old. It won't represent the current state of the art, and it is generally inadvisable to buy second-hand equipment of a mechanical nature. Much may have gone wrong or may be on the verge of going wrong.
Still, the Project/One may be an exception. If you plan to buy it, ascertain how well it performs in playback and in record/playback. Do your ears tell you that it does well in such respects as extended and flat frequency response, low distortion, low noise, and steady and accurate motion? Does it offer the proper equalization and bias facilities for at least Type I and Type II tape? Does it have the features you consider desirable? If the answer is yes to all of these questions, and the price is low, the risk may be worth taking. I wouldn't advise your spending more than $100, however.
(Source: Audio magazine, Apr. 1987, HERMAN BURSTEIN)
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