TAPE GUIDE (Nov. 1985)

Meter Discrepancy

Q. When I record at +6 dB for peaks (which is what I'm supposed to do, according to the manual for my cassette deck), on playback the level is considerably higher, easily reaching +8 dB or more. Why is this? It doesn't matter at what level I record; the deck will always boost the levels in playback.

When recording, should I concentrate on the record or the playback levels?

-Richard C. Reyes, Tacoma, Wash.

A. Some tapes have greater sensitivity--the amount of signal output for a given signal input-than do others.

You may be using such a tape, which would account for the elevated meter reading in playback. That is, the tape you are using may have greater sensitivity than the tape used by the deck manufacturer to calibrate the meter's playback reading. Or it could be that the meter is mis-calibrated. Concentrate on the record levels unless the high playback levels correspond to noticeable distortion; if that's the case, adjust the record levels accordingly, reducing them, say, 2 or 3 dB.

Digital Readiness

Q. I have heard that there are cassette decks and tapes which claim they can faithfully record CDs. Can they faithfully reproduce the high energy levels of Compact Discs without overload? That is, can they achieve as great a signal-to-noise ratio and frequency response?

-William Scaramazza, Swedesboro, N.J.

A. On an absolute basis, without regard to audio signal, there is no analog cassette deck and tape combination today which can match the S/N of a Compact Disc and player. CDs achieve over 100 dB S/N on a weighted basis, while cassette decks achieve weighted S/N in the mid-70s with Dolby C NR and in the mid-80s with dbx NR.

However, the dynamic range of the original audio material seldom reaches or exceeds about 70 dB; usually it is no more than 65 dB and often is a good deal less. Hence, a quality cassette system can ordinarily encompass all that is on a musical CD with some margin of safety to spare. If you play the program material at extremely loud levels, during quiet passages you may hear some faint noise with Dolby C NR and perhaps even with dbx NR, but in most listening situations noise is an insignificant factor with modern noise-reduction systems.

Compact Discs have frequency response extending to 20 kHz and drop ping very sharply beyond that. High-quality cassette systems achieve response to 20 kHz and sometimes somewhat higher, perhaps to as much as 24 kHz or so, thanks to such developments as metal tape, Dolby C NR (with its anti-saturation treble-boost curve), and Dolby HX Pro (which reduces bias when there is substantial high-frequency program content that acts in the same manner as bias). Such response is more likely with separate record and playback heads.

Print-Through

Q. I record FM broadcasts onto cassettes. When I stop recording, the signal on the tape doesn't stop immediately. It lingers for a second or so, as if someone turned down the volume. This is annoying when I want a blank space between songs.

-John Turner, Greensboro, N.C.

A. The faint sound you hear after stopping your deck is probably due to print-through, a transfer of the signal on one tape layer to the adjacent layer caused by the magnetic flux emanating from the tape. A lower recording level helps reduce print-through, but of course at the cost of a lower signal-to noise ratio; if you are using Dolby C NR or dbx NR, you may well be able to afford such a reduction in S/N. Also of help is the use of a tape that is not as thin as the type you may be using-for example, C-60 instead of C-90. (Are you by any chance using C-120, which is usually advised against?) You might also be able to reduce the print-through by putting the cassette through fast-wind and rewind before playing it; however, the print-through will likely return with storage.

Perhaps you can erase the offending sound by backing up the tape and putting it through momentary erasure; that is, recording the desired blank space with no signal input. Consider-able care will be needed to erase only the section you want erased. It would be wise to practice with a cassette that you don't care to preserve.

Disturbing Playback Readings

Q. When I use a TDK SA tape, the meter is in the red during playback even though it wasn't when recording. With a Maxell UD tape, the playback reading is the same as in recording. And with a BASF CRII, the playback reading is lower than the recording one. Does this mean that I should use only the Maxell tape? Or could I also use the TDK tape, provided that I use a lower recording level so as not to be in the red during playback? If so, won't I then have a reduced S/N ratio? In the case of the BASF tape, should I raise the recording level, thereby improving the S/N ratio? Or should I altogether disregard the playback readings? This leads to a related question: Just what does a record-level meter indicate?

-Marc Claessens, Toronto, Ont., Canada

A. The varying playback readings of the three tapes you mention reflect their different sensitivities. Sensitivity is the level of tape output for a given signal input to the tape. It appears that your deck's meters have been calibrated by its maker on the basis of the Maxell UD tape or one very much like it. There is a pretty good chance although not a guarantee-that you will get the best Dolby tracking with this tape or a similar one. Dolby tracking signifies that internally the input and output levels are matched. Thus the variable treble boost in recording will be exactly complemented by the van able treble cut in playback, and accurate high-frequency response will be achieved. However, Dolby tracking can vary about ±2 dB without grave consequences. Therefore it may be quite all right to use tapes other than Maxell, provided that playback readings do not differ greatly.

Your choice of recording level should not be guided by playback readings. For each kind of tape, you should experimentally determine maxi mum recording level; that is, ascertain how high you can go before distortion and/or treble loss become evident, and then back down 2 or 3 dB for a safety margin.

The record-level meter indicates how much signal is being applied to the tape. For a peak-reading meter, 0 dB record level typically corresponds to a signal level that, at 315 Hz, results in a recorded level of 250 nano-webers per meter on the tape.

Sometimes 0 dB corresponds to 200 nWb/m in the case of a peak-reading meter. In the case of average-reading meters-true or nearly true VU ones--0 VU tends to denote a level approximately 8 dB or so lower, providing a safety margin to cover the meter's tendency to lag behind transients; here 0 VU would denote a recorded level of about 100 nWb/m.

Reluctant Cassette

Q. I have a cassette of Itzhak Perlman performing the Brahms Violin Concerto. The first time I played it, the tape was excellent in all respects. However, the next time it presented problems. The sound was of very wavering pitch, and I could not rewind the tape or make it run in fast-forward. I would appreciate your advice.

-Julius L. Levin, Glencoe, Ill.

A. It seems that you have a defective cassette, which should be returned to the dealer for exchange or refund. Before doing so, you might try rapping the cassette smartly against a table top or similar surface, but not so hard as to damage either one; perhaps you could use a few intervening layers of cloth or newspaper. It may be that the tape has "static cling" and that rapping the cassette will loosen the layers of tape.

Y-Connectors for Duplication

Q. I was recently asked to make several copies of a sales-training cassette. I dubbed it onto open reel, and then connected the output of the open reel deck to three cassette decks via Y-connectors. Since the recordings are of voice, frequency response is not critical. Does Y-connecting degrade the signal? How many recording decks can one Y-connect? What is used in a commercial duplicating system to connect the slave recording decks to the master playing deck?

-Paul Lee Hargitt, Jr., Indianapolis, Ind.

A. When you connect the inputs of two or more tape decks directly to the output of another deck using Y-connectors, the input impedances of the copying decks load each other and the source deck. The result may be distortion and/or loss of treble response, depending on the various output and in put impedances involved. The extent to which this occurs depends on the particular decks in question, and its audibility depends on the program material. Degradation of the copies' signal is probably a good deal less serious for voice than for music.

If the results you've gotten are acceptable, stay with your procedure. I don't know how many more "slaves" you can add before the results be come objectionable; you will have to determine this by adding one slave at a time. Some slaves may interfere more with the system than others will.

In professional duplication, the copying decks are fed through buffer electronics that isolate the inputs of the slaves from each other and prevent the slaves from heavily loading the master playing deck.

Din on DIN

One of the items in the June 1985 "Tape Guide" dealt with the meaning of 0 VU on record level (and playback level) meters. W. J. Newell of Richard son, Tex., presents interesting and useful information in this context:

"The reference Dolby level is based on the ANSI standards, while DIN levels are based on (surprise!) DIN standards. They do not have the same basis. DIN specifies that magnetic fluxes on tapes be measured directly with a magnetometer, while ANSI specifies that flux be determined by playing the tape with a 'high-efficiency' head. The practical effect of this is that the same piece of tape will play about 1 dB higher on a DIN-calibrated meter than it will on an ANSI-calibrated meter, assuming the 0-dB reference is the same nominal flux level for both. Looking at it another way, given a meter with its 0-dB reference at 200 nWb/m ANSI (Dolby 0 dB), a Dolby reference tape should read 0 dB while a DIN 0-dB tape (250 nWb/m to the DIN standards) will read about +1 dB, not +2 dB as most of the cassette-deck testers in the world continue to state.

"I think that the older 160-nWb/m standard for 0 dB refers to the DIN standard. Thus, a Dolby-level tape should read about +3 dB on a meter with its zero set to this level.

"Are these differences significant? Yes. Many errors may occur in the record/playback chain for Dolby tapes, and there is no need for any more.

Even if this were the only error, it might be audible on Dolby B to a critical listener, especially in a comparison situation; for Dolby C it certainly would be heard. If Dolby types are mixed, the effects can even be more bizarre."

(Source: Audio magazine, Nov. 1985, HERMAN BURSTEIN)

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