by Rupert Neve
Tape recorders were first used by professional recording studios in the late 1940′s, soon after WW2. They were adapted from the German Magnetofon that had been used by the German Navy to improve security of communications with their submarines.
It could be claimed that the magnetic tape recorder was the device that really made the modern music recording industry possible. Before that time recordings were cut on lacquer or wax master disks. Although the sound quality of the long playing record achieved a very high standard, no editing or “dubbing” was practical.
The tape recording channel consisted of a “Drive” amplifier that fed the magnetic “Record” head winding through a constant current circuit. A replay amplifier, connected to the “Playback” head, with suitable equalization, then amplified the very small signals from this “Playback” head to restore line level. Because of the high impedances and the impossibility of controlling this dynamic process by, for example using negative feedback, the process was somewhat non-linear, exhibiting compression at high levels, noise at low levels and considerable 3rd. harmonic distortion at the low frequencies. The frequency response depended on many factors such as the quality of tape, the head design and, not least, frequent expert maintenance required to optimize the performance on a daily basis.
In spite of the limitations, “Tape” sound, in the hands of a professional who knew how to get the best from the medium, was pleasant, enhancing the sound of many instruments and smoothing over deficiencies in some of the more aggressive sounding microphones.
With these factors in mind, together with nostalgic memories of tape recordings over many years, we set about reproducing the classic sound of tape!
Because of the non-linearity referred to, tape distortion varies with signal level. When the level is very high, the signal is compressed and if it is too high it will clip. (which is a highly unpleasant sound!)
In order to avoid the need for adjustment of both record and playback levels, these two controls have been ganged so that as the record level is increased, the replay level is decreased.
The tape level meter provides a good reference that, with care, will indicate the approximate maximum record level of an actual recorder.
You can expect to experience a classic risein frequency response around 300 Hz and a slight ringing due to the pre-emphasis at around 12 to 15 kHz., depending on the setting of the 7.5/15 i.p.s. switch. Low frequency Third harmonic distortion is probably the most immediately audible effect that you will hear. The effect on certain musical instruments is quite incisive, producing the characteristic coloring of a real tape recorder.
However, tape recorders are actually very good and these effects are not always obvious to the inexperienced listener. We did not set out to make a “bad” tape recorder!