So you have just made a technically perfect recording of a piece of music with true beauty and meaning. You take the tape off the machine and put it carefully on the shelf ready for mixing tomorrow. Tomorrow comes and you play the tape - it isnt at all like you remember it, all the loud percussive sounds have strange echoes, not only after the initial sound but before it too. This is print through. Particularly during the first twenty-four hours after a recording is made, the magnetic force of each loud sound will seep through perhaps two or three layers of tape in both directions causing pre- and post-echoes. Other than fast winding the tape a couple of times in each direction (which doesnt make very much improvement) there is no safe cure for print through. It has messed up your recording forever. Two methods of reducing the effects of print through are to use noise reduction and to store the tape tail out. Although there will physically be print through on a digital tape, it wont affect playback in the slightest. Score so far: Digital 4, Analogue nil.
All analogue recorders are aligned so that the gaps of the record and playback heads are precisely at 90 degrees to the direction of tape travel. If this statement were true, then head alignment wouldnt be a problem. In practice recordings are made on machines with wrongly aligned heads which then will not play correctly on a properly aligned recorder. This causes a loss of high frequencies and has a damaging effect on the stereo image. Although the alignment of digital heads is important, a small deviation wouldnt make any difference at all to the sound, and since the head alignment isnt user adjustable no one can get it wrong apart from the manufacturers who really ought know what they are doing!
Even if the heads of a multitrack recorder are aligned as well as it is possible to align them, there is still the manufacturing defect known as gap scatter. This is when the gaps of the individual record or playback elements of the head are not all at exactly the same angle. This makes it impossible to align the head properly for all the tracks. In rotary head recorders of all types, including ADAT, there can be no gap scatter.
Analogue recorders are very moody. Their performance changes with the state of wear, type of tape, the weather and any of innumerable variables. An essential task involved in operating an analogue recorder is line up. At the small studio level, line up will be performed rarely but (hopefully) regularly. Major studios consider line up as important as tuning a piano. You wouldnt be happy if you were paying several hundred pounds for a day in the studio and find that the piano is out of tune. You also wouldnt be happy if the recorders were not working at the peak of their performance. Digital recorders do need lining up, but this is a job for specialist engineers, and as long as they are running within specifications the tape will record and play back perfectly.
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