In this section we'll be looking at the various operations which periodically take place in order to keep a multitrack recorder in good shape.
These machines have electrical circuits and mechanical parts which must be calibrated with great care in order to obtain as faithful a sound reproduction as possible. Usually, the calibration of the electric part is done by applying a 1KHz sinusoid with a 0Vu amplitude to the input line (the effective voltage value of 0Vu in certain machines is stated by the manufacturer). This test signal is passed through the internal circuits which have all been calibrated and set at 0Vu. Then the signal is routed to the recorder's output and monitored at the mixer's input. Once this is done, we then record on a trial ribbon whose fluxivity varies and at the various available speeds. Once again, the circuits must be calibrated in such a way that the input and output signals are both at 0Vu. The bias current is also calibrated so as to not saturate the ribbon. Finally, the phase difference between the heads is adjusted by applying a square wave to each of them and checking the outputs on the oscilloscope. The square waves are all brought back into phase by accurately calibrating the position of each head.
As we have said, as well as the electric calibration, there is also the mechanical part to be considered. Wrong positioning of the heads could create distortions when it makes contact with the magnetic ribbon.
The heads must all have the same height otherwise during recording the signal could be stored in one zone of the ribbon, whilst during reproduction the head makes contact with a different zone (higher or lower) with a consequent loss of signal.
The following figure illustrates a wrong height alignment between the reproduction head and the recording head:
The head's angle could bring about an uneven distribution of pressure on the ribbon:
If the head is too far forwards compared to the ribbon's position, the latter risks wrapping it excessively:
The head's angle in relation to the ribbon. The head's axis must be perfectly perpendicular to the ribbon's direction:
To put all these operations into practice requires experience and competence. Our intent was to make the reader aware that the quality of sound depends on many factors, some of which may sometimes seem irrelevant. At the end of the day, total commitment to each of these details will give a good, all-round result, rewarding for both the practitioner and the listener.