The tape recorder is the principal instrument of any electronic music studio. The technical quality of the composition is limited by the decks used, and may be further compromised by how the decks are used.
The basic factors that determine the possible quality of a recording made on any anlog deck are tape speed and track width. (Surprisingly, the electronic design of the deck has a relatively small effect on quality as long as drastic flaws are avoided. The difference in price among various decks of the same format primarily reflects durability of the machine.) Speeds and widths in common use today are:
speeds widths tracks 30 ips 2" 16-24 15 ips 1" 4-16 7 1/2 ips 1/2" 2-16 3 3/4 ips 1/4" 1-8 1 7/8 ips 1/8" 2-8 (cassette)
You can probably find decks that run at all combinations of these, but as a general rule, the wide tapes are run at the faster speeds. The ubiquitous cassette finishes last at 1 7/8 ips on 1/8" tape. The track width depends not only on the width of tape but on the number of tracks stuffed on the tape.
The track numbering of 1/4" four track format tape is a little confusing. The tracks are actually numbered from top to bottom 1,2,3,4; but since the 1/4 track stereo consumer format records left channel on track 1 and right channel on track 3, you occasionally see controls grouped 1,3,2,4. If you are constructing tape for four track playback, use 1=left front, 2= left rear, 3=right front, 4=right rear
All tape decks have two main systems; some mechanical apparatus for moving the tape past the heads, and electronics for recording on and playing back from the tape. Sometimes these parts are physically as well as conceptually separate, but most often they are in the same box.
Tape is threaded from left to right on most modern tape decks. Tape starts from the SUPPLY REEL, runs past one or two TAPE GUIDES or TENSION ARMS, past the ERASE, RECORD, and PLAY HEADS (remember the order), between a CAPSTAN and PINCH ROLLER, past more guides and arms, and finally onto the TAKEUP REEL.
Motion of the tape is controlled by the capstan. This is a steel shaft which is always turning at a constant speed. When the PLAY button is pushed, the rubber pinch roller squeezes the tape against the capstan and the tape is pulled past the heads. The TAKEUP MOTOR winds the tape onto the takeup reel as this goes on. Some back tension is necessary to keep the tape tight against the heads. This is generally applied by providing a little power to the SUPPLY MOTOR (Which always runs backwards; it may also be called the rewind motor.), although there are other methods.
When the tape is to be rewound, the pinch roller stays away from the tape and full power is applied to the supply motor making the tape zip backwards. (A low power is applied to the takeup motor to keep the tape tight.) To save wear and tear on the heads and to suppress some loud annoying sounds, one or two TAPE LIFTERS pop up to pull the tape away from the heads during this operation. When the machine is in the FAST FORWARD mode, the same sort of things go on, but this time the takeup motor gets full power.
There are brakes on both reel motors to stop the tape quickly and gently. Because the tape and reels can build up a fair amount of momentum, care must be taken in going from one of the fast modes to the play mode to avoid damaging the tape. Machines vary in their approach to this problem:
In any case, you have to spend time getting to know your machine.
I mentioned earlier that the tape lifters pop out during the fast modes to keep the tape off the heads. Some decks do this in STOP mode too. (This is cheaper, since the lifters can be attached to the pinch roller mechanism.) In either case, we often want to hear the tape in fast or stop modes, so the better machines have a way to defeat the tape lifters. There are different names and different versions of this process; here are the most common:
The most advanced decks have a SHUTTLE lever that enables you to do all of these without actually touching the tape.
Somewhere along the tape path is a gimmick that prevents the transport from working unless the tape is threaded tightly. This may involve a tension arm, a small wire switch, or even a light and sensing device.
These controls are the ones you will be using the most:
The basic electronic requirements for a tape deck are an amplifier and bias oscillator for recording and a preamplifier for playback. With the most expensive decks that is all you get. Less expensive machines are usually bristling with extra features to attract the consumer. Here are a few of the extras you will find.
These are not really an option, but decks vary widely as to style and quality of these.
These developed in the old days of radio, when they indicated the percentage of legal modulation a station was generating. They also had a dB scale, with 0dB at the 100% modulation point, which is the only scale we pay attention to any more. On most tape decks, the 0dB point is some standard recording level.
There are two vital factors to keep in mind when you are using VU meters:
1. They measure the average signal, and move rather slowly. This means brief peaks will not be properly indicated and may distort. As a hedge against this problem, many meters now have a red light that lights when the signal hits +6dB. The actual recording level you use will depend heavily on the material. As a general rule, keep the meter just below 0dB, with short excursions into the red zone allowed.
2. They do not have a flat frequency response. Most meters exaggerate the low frequency readings and do not respond to signals above 8 khz very well. A good rule is to keep bright signals down an extra 6 dB. (An especially good idea, since high frequency signals are the most likely to be distorted in the recording process.)
These are seen mostly in European and Japanese gear. They look much like VU meters, but they do not average the signal. Instead they jump to the highest level and fall back rather slowly. If a signal were measured on both a VU and a peak meter, the peak reading would appear higher-- tape deck manufacturers compensate for this by moving the numbers. The result is that you record the same way on either, keeping the music just above 0 on the loudest parts.
Zero on a peak reading meter corresponds to +4 on a VU meter.
These are very much in style on Japanese cassette decks. They actually perform better than VU meters as far as frequency response is concerned, but do not average in quite the same way. The main disadvantage is that cheap ones do not have enough segments to properly show what is going on. The best ones combine the peak and VU functions, with the highest led staying on longer than the others, which means you can always see the higest level reached in the last two or three seconds.
The meters on most cassette decks are peak meters.
Most tape decks have numerical readouts that keep track of your location on the tape. These may be electronic or mechanical in design, but that really makes no difference. What really matters is what the counters count. The inexpensive kind (found on most cassettes) count turns of the takeup reel. (Actually about four numbers go by for each turn.) Since the amount of tape wound varies according to direction of operation as well as location on the tape, these meters are only useful for coarse operation. Counters on more expensive decks actually measure the tape with a special wheel and are quite accurate. Tape decks occasionally have auto stop or locate features which react to the tape counters.
Professional quality decks usually do not have output level controls, because level is best controlled at the mixer. (The fewer controls there are, the less the chance of a mistake.) When such a control is provided, there is usually a switch (or sometimes a "click" on the knob) to set the output at calibrated level.
In order to get a good recording, the tape must be in very intimate contact with the heads. The wave length of a 15khz tone recorded at 15 ips is one thousandth of an inch, and a separation of half that amount can be expected to cause some loss of signal. This is not much thicker than a fingerprint. You can not expect good results unless the heads are clean.
Cleaning heads is simple, just dip a cotton swab in some 91% isopropyl alcohol ( never rubbing alchohol) and scrub each head. If there is anything on the head that will not come off with this method, use another deck and alert the technician. Cleaning at the beginning of your session should be adequate, unless you get carried away with the grease pencil.
If you notice a build-up of tape oxide on the capstan, pinch roller or tape guides, you may clean these also. Do not clean anything else.
This process applies to analog audio tape decks only. While DATs and VCRs need to be cleaned too, the procedure is different.
Occasionally, a tape head or guide will pick up a permanent magnetic field. This is caused by physical jarring of the machine, and will result in mysterious noises on the tape, or in extreme cases some high frequency losses.
You should only demag when there is magnetism present, because the most common cause of magnetism is improper demagging! To definitively detect magnetism you need an expensive meter, so most technicians demag on a regular schedule.
A demagnetizer is a small wand with an electromagnet in the tip. When turned on, it produces a very strong 60 hz field. If this field is slowy brought near and then away from a piece of metal, any magnetism on the metal will be removed. If the field is switched off while near metal, the metal will be strongly magnetized.
So, the procedure for demagging a tape deck is simple. Turn deck power off. Hold the wand at arms length away from the deck and turn it on. Slowy bring it along the tape path, moving it back and forth near but not touching all metal parts- slowly rotate the capstan while the wand is near it- then move the wand away and turn it off.
Describing the electronic setup procedures is beyond the scope of this essay, and at any rate you should follow the step by step instructions in the manufactures maintenance manual. But here is a synopsis of what has to be done.
The best decks will only give results comparable to their use. In addition to the detailed instructions in the rest of this chapter, the following tips are offered in the interests of quality recording.
Label your tapes carefully and thoroughly. Proper labeling reduces the number of times a tape must be played. Include:
You may put this information on the box or on the tape reel. (The name of the tape and your name must be on the tape reel of course.) I like to number my reels and put most of the information on the box.
Keep tapes tail out. (That means in the just played rather than the just rewound state.) This will reduce print-through and deformation of the tape.
Put leader at the beginning and end of important tapes. The very ends of tape get pretty beat up.
Place calibration tones at the beginning of finished tapes. This simplifies the process of making copies. The easiest way to do this is to record an entire reel at your favorite calibration level (such as 0vu) and frequency (say 700 hz) and cut off sections as they are needed. Separate the tone from the piece with a long leader so there is no print through.
Use noise reduction where appropriate, but do not use noise reduction where it is not needed. Synthesizer licks, with their restricted dynamic range and pure, easily distorted tones, are usually better off without noise reduction. So are sounds at extremely high or low frequency, and sounds that are pretty much continuous.
Keep the number of generations to a minimum. For example, if you have pitch shifted a sound, and later decide you like the result better if it is also flanged, you will be one generation ahead if you back up a step and pitch shift and flange the original source on one pass.
Keep your levels high. You can always turn sounds down in the final mix, but if you try to raise the volume of weakly recorded material, you will get a lot of noise.
Spot distortion early and redo the process if necessary. Distortion grows as tapes are copied, and it cannot be removed once it occurs.
Mastering is the creation of a final version of your project, ready to duplicate. This is done by the duplication house, because you aren't likely to own a Sony PCM 1630 (a digital recording system based on 3/4 "videotape). Premastering is making the tape you will send to the dupe house. Usually a premaster is a first generation mixdown, but if your project has several cuts, the premaster will be assembled from the best mix of each.
Here are the rules.
This is taken from literature put out by one popular dup house. They all differ slightly in their requirements.
Send the Master, but keep two copies.