TAPE GUIDE (Dec. 1987)

More on Tape Counters

In the May 1987 issue, I mentioned some formulas from reader Jeff Bonwick, a math major at the University of Delaware, which could be used to determine elapsed time on a tape from the numbers on the tape deck's counter. Now, reader Michael P. Lucido of San Jose, Cal. has incorporated this information into a computer program written in BASIC for PC compatibles (and for some other computers that speak the same language).

Copies of the program are available by mail to anyone who sends a stamped, self-addressed envelope (#10 or larger, please!) to: BASIC Tape Program, c/o Karen Clark, Audio Magazine, 1515 Broadway, New York, N.Y., 10036. (Copies of the original formula and procedure are also available; request "Tape Formula" instead. If you want both, send only one envelope with a request for both.) For those who lack access to a computer, or whose computers use a different dialect of BASIC than PC compatibles, Mr. Lucido is willing to pre pare charts for any tape and recorder combination, for $2 each. Interested readers should send him the following information: The tape brand, variety, and length (e.g., Maxell XLII-S, C-90); the tape-counter reading after 10 minutes of play, and the counter reading after 20 minutes of play. Payment and a self-addressed, stamped envelope should accompany the information. Mr. Lucido may be reached at Lucid Enterprises, P.O. Box 32436, San Jose, Cal. 95152.

Please do not address requests for any of this material to me, since only Audio has copies of the program and formula available for mailing, and only Mr. Lucido is equipped to prepare the custom charts.

Feeding Multiple Decks

Q. Through separate outputs, I have connected an open-reel deck and a cassette deck to my control amplifier. However, this leaves me without an output to feed my VCR. Would it cause distortion if I were to connect the cassette deck and the VCR through a Y-connector to one of the outputs of my control unit? Assuming that I would operate only one deck at a time, would I degrade the quality of the signal being recorded?

-Ernst K. Renner; Mount Vernon, Ohio

A. Your proposed connection has a good chance of working without significant audible effects, but I cannot promise this. Sometimes two pieces of audio equipment connected to the same jack of another unit will load each other significantly, but often they will not. Effects of loading may include loss of treble response as well as distortion. I suggest that you experiment, for no harm will come to your audio components.

A better solution is to purchase a tape-deck switchbox (available from several companies, including dbx, Russound, and Radio Shack). These permit three or more decks to be connected to one set of tape inputs and outputs. One of these switchboxes would permit you to connect one deck at a time or all decks at the same time.

Thus, to satisfy your curiosity, you could play around to learn the effects of loading, as far as your equipment is concerned.

Taping Via VCR

Q. What do you think about using a VCR for recording sound only? I have many old records which I would very much like to put on some form of tape.

Because audio tapes have limited capacity, it is impossible to get more than a very few records on them. I have read that a VCR's frequency response, even a state-of-the-art machine's, is very poor. I need your advice.

- Clifton T. Chadwick, Wheat Ridge, Colo.

A. If you use a Hi-Fi VCR, whether VHS or Beta, you can get excellent performance in every respect, even at the slowest videotape speed. Frequency response will be wide and flat, signal-to-noise ratio will be very high (in the vicinity of 80 dB), distortion will be very low, and motion (speed accuracy, wow and flutter, etc.) will be excellent. Just be sure to use good tape, for minimal dropouts.

The Hi-Fi VCR is a relatively new breed and is substantially more expensive than the ordinary VCR. In Hi-Fi mode, it records the sound on the same diagonal tracks as the picture, as a frequency-modulated r.f. carrier. (This is the same technology that is used in FM radio but with different carrier frequencies.) Hi-Fi VCRs also record audio directly, like ordinary audio tape decks, along one edge of the tape. This is done to maintain compatibility with conventional VCRs, which have only these longitudinal soundtracks. If you record audio on the longitudinal tracks of either type of VCR, performance will be substantially below that of a Hi-Fi recording. For example, signal-to noise ratio will be on the order of only 45 dB, and frequency response will be appreciably degraded from about 10 kHz up.

Do not confuse Hi-Fi VCRs with HQ VCRs. The HQ label refers to four circuits which improve picture quality. If a VCR has at least two of these circuits, it can boast the HQ emblem.

You might also be interested in what another reader has to say about the pros and cons of taping audio on videocassettes:

Having transferred my open-reel tape library of over 200 hours to video cassette, I have had appreciable experience with the process. My reason for transferring from open-reel to videocassette is that, by the time the heads wear out in my open-reel deck, it is likely that replacement heads or a replacement recorder will be unavailable. The convenience of a videocassette, its longer playing time, and the absence of tape squeal or tape rubbing against the reel are all bonuses.

Also, I have never seen a recorder with a flatter frequency response from 20 Hz to 20 kHz. For this, I guess l can live with a dropout about every 25 hours.

Dropouts (and impulse noise) are most likely to occur on the initial portion of the tape. Prerecorded videocassettes leave the first 45 S blank, and this is also good policy for audio recording. Some dropouts will disappear with rerecording, but occasionally one will persist at a given place on the tape despite all precautions. Also, some dropouts will appear on the second playing of a tape that did not appear on the first playing.

The dropout problem seems to vary with the videocassette and the VCR.

As far as the tape is concerned, it seems to depend more on the individual cassette than on the brand. I have used tapes from a number of manufacturers and have encountered dropouts with all of them. After rewinding a videocassette, it helps to blow out the loose oxide that accumulates on the plastic guide at the cassette's head side. Cleaning the heads of the VCR with a head-cleaning cassette does not seem to have an effect on drop outs. However, the brand of VCR does; I have two, and one is better than the other with respect to dropouts.

Another disadvantage of VCRs is that unless the machine has flying (moving) erase heads, editing is not practical. There is too much space be tween the erase and play/record heads to delete an unwanted portion without erasing some later material that might be wanted.

There is another reason why editing does not work well with a VCR. In most VCRs, the erase head operates in a line perpendicular to the tape motion, as in open-reel or audio cassette re cording. However, recording with a VCR is done on tracks which cross the tape diagonally. Therefore, in deleting a portion of a recording, part of some recording lines are left on the tape at the start of deletion, and there are some partially recorded lines at the end of the deletion. The result is a noisy cut. Recorders with flying erase heads are expensive, but they erase diagonally, track by track, so that clean cuts are possible.

-John H. Markell; Sun City, Cal.

Rating Wow and Flutter

Q. I'm confused about what wow and flutter really are, and about their audible effects on music. One manufacturer claims that its cassette deck, with a wow and flutter spec of 0.025% wtd. rms, doesn't exhibit the audible effects of a deck with a wow and flutter spec of 0.05%, especially on piano music. There is a deck I would like to purchase, but it has a wow and flutter spec of 0.05%. How would you rate a value of 0.05%?

-Gabriel Vazquez Padua, Bayamon, P.R.

A. Wow and flutter refer to cyclic changes in tape speed. Wow refers to changes that occur at a slow rate, say less than 10 times per second. The audible result is a wavering pitch. Flutter refers to more rapid changes in tape speed, say above 100 times per second. The result is a grainy or gargly quality to the sound.

My guess is that most people are not sensitive to wow and flutter until they exceed 0.05% wtd. rms, perhaps not until they exceed 0.1% or even 0.2%. It should be noted that the NAB (National Association of Broadcasters) Standard for cassette decks provides that wow and flutter shall not exceed 0.2% wtd. rms. On the other hand, the NAB Standard for open-reel recorders provides that weighted flutter shall not be al lowed to exceed 0.05% at the 15-ips speed, 0.07% at 7 1/2 ips, and 0.10% at 3 3/4 ips.

The audibility of wow and flutter depends not only on the individual's sharpness of hearing but also on the nature of the program material. Wow and flutter are more apt to be evident on a single sustained note than on complex tones such as a symphony orchestra going full blast. All in all, I doubt that you will have a problem with a deck that keeps wow and flutter to a maximum of 0.05%, but I can't promise. You should listen to your prospective deck before you buy it.

Speed and Width Options

Q. In open-reel decks, which format provides better fidelity: 7 1/2-ips speed coupled with quarter-track heads or 3 3/4-ips speed coupled with half-track heads?

-P. D. Sharma, Lakeview Terrace, Cal.

A. Let's refer to 7 1/2 ips with quarter-track heads as format A and 3 3/4 ips with half-track heads as format B.

Overall it seems that you are better off with format A.

At 7 1/2 ips, you have better high-frequency response and better tape motion (less wow and flutter). The wider track of format B gives you a signal to-noise ratio about 3 dB greater, but this fairly modest advantage tends to be cancelled by the greater tape-head output at 7 1/2 ips. In the matter of high-frequency loss due to azimuth mis alignment, format B is at a disadvantage because the effect of a given degree of misalignment becomes more severe as track width is increased and as tape speed is reduced. The effect of tape dropouts is reduced as track width is widened, giving format B an advantage in that respect-but the ad vantage is slight, because dropouts tend to be minimal when high-quality tape is employed. With respect to headroom, format A has the advantage. At the higher tape speed, less treble boost is needed in recording to preserve treble response. Thus, there is less risk of tape saturation (which results in distortion and treble loss) when recording strong treble frequencies at a high level.

Still, very good results can be had at 3 3/4 ips. Using a high-quality deck, it is quite possible that you would hear little difference, if any, between the two for mats. Moreover, format B provides the same recording time per reel as format A but without the need to reverse the reels.

Effect of Dirty Heads

Q. I have read that there is a loss of treble if tapes are played back on decks with dirty heads. Will this hap pen even if I use a top-quality tape? Will the tape suffer a permanent loss of high-frequency response?

-J. Bill Such; Natrona Heights, Pa.

A. Dirty heads cause the tape to be slightly separated from the heads, causing treble loss in playback even if the tape is of high quality. However, the loss does not occur on the tape itself; it occurs only in the playback process. Treble response should be restored once the heads are cleaned. However, if the heads are magnetized, this can cause permanent treble loss on the tape itself.

An Accumulating Problem

Q. How long after a tape is wound and stored does the process of print-through begin and become noticeable? Is the process cumulative?

-Ed ward Bauman; San Diego, Cal.

A. Print-through tends to occur mostly in the first few hours of tape storage, and cumulatively increases at a slower and slower rate with the pas sage of time. To illustrate, for a particular tape, print-through might be 54 dB below the desired audio signal's peaks 8 hours after storage; it might rise about 1 dB in the next 16 hours, another 1 dB in the next week, another 1 dB in the next three weeks, 2 dB in the following 11 months; and 1 dB in the next 10 years. Thus, print-through might eventually be about 48 dB below the audio level.

Two Heads Better Than Three?

Q. I am considering the purchase of a cassette deck which, according to my dealer, is the best in its price range. However, it is a two-head deck and only has Dolby B noise reduction.

Is it possible for this deck to perform better than others in the same price range which have three heads and which offer Dolby C and dbx NR as well as Dolby B? What is the function of a third head?

-Glenn Sefton; Carmel, N.Y.

A. In a two-head deck, one head serves for both recording and play back; the second head erases the tape prior to recording. In a three-head deck, separate heads are used for re cording and playback. This permits each head to be designed for optimum performance of its single function, A playback head requires a very narrow gap in order to maintain response throughout the upper treble range, whereas a record head requires a gap about five times as wide to achieve best results by fully penetrating the tape's magnetic coating. Where one head serves for both recording and playback, a design compromise must be made. Still, a carefully engineered and well-built record/playback head can achieve very good performance.

A three-head deck has an added function that is often useful: It permits simultaneous monitoring (playback) and recording so that a recording can be continuously compared to the source. This helps guard against poor results due to human error (such as setting bias and equalization for the wrong tape type). And it can be useful in adjusting bias, when the deck pro vides a variable bias control.

Overall, a well-designed and well-made two-head deck using Dolby B NR can outperform an indifferently de signed and indifferently made three-head deck boasting Dolby C and/or dbx NR. It stands to reason that no moderately priced deck will be state of the art even if it does boast three heads and three NR options.

Extended frequency response (made possible by a separate playback head) and very low noise (made possible by Dolby C or dbx NR) are not the sole attributes of good performance. Other important attributes include flat frequency response over most of the audio range, low distortion, low scrape flutter, and steady and ac curate tape motion. Perhaps it is in these respects that the recommended two-head deck outperforms the three-head decks in the same price range.

There is also the question of reliability:

How long will the deck continue to give good service before requiring head re placement, repair, etc.? Again, the recommended deck may excel here.

(Source: Audio magazine, Dec. 1987, HERMAN BURSTEIN)

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