Equalization
For a number of reasons, both the signal that is imprinted upon the tape by the action of the record current in the record head and the signal arising as a consequence of the induced current in the playback head are heavily distorted with respect to frequency and must both be equalized. This is an area where standardization between different manufacturers is particularly important because, without it, tapes recorded on one machine would not be reproducible on another.
In itself, this would not be such a problem were it not for the fact that, due to differences in head geometry and construction, the electrical equalization differs markedly from manufacturer to manufacturer. The IEC provided an ingenious solution to widespread standardization by providing a series of standard prerecorded tapes on which are recorded frequency sweeps and spot levels. The intention was that these must be reproduced (played back) with a level flat-frequency response characteristic, with the individual manufacturer responsible for choosing the appropriate electrical equalization to affect this situation. This appears to leave the situation concerning record equalization undefined, but this is not the case because it is intended that the manufacturer chooses record equalization curves so that tapes recorded on any particular machine must result in a flat- frequency response when replayed using the manufacturer’s own IEC standard replay equalization characteristic.
The issue of “portability” should not be overlooked, and any serious studio that still relies on analogue recording must ensure that its analogue tape equipment is aligned (and continues to remain aligned—usually the duty of the maintenance engineer) to the relevant IEC standards. This, unfortunately, necessarily involves the purchase of the relevant standard alignment tapes.
Tape Speed
Clearly another (in fact, the earliest) candidate for standardization was the choice of linear speed of the tape through the tape path. Without this the signals recorded on one machine replay at a different pitch when replayed on another. While this effect offers important artistic possibilities (see later in this chapter), it is clearly undesirable in most operational circumstances. Table 26.1 lists the standard tape speeds in metric (centimeters per second, cm/s) and imperial measures (inches per second, ips) and their likely applications.