Rupert Neve Portico 542 - 500 Series Tape Emulator with Silk User Manual
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NOTES ON TAPE
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 on the
542 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.
542 USAGE NOTES
While in the olden days, tape’s non-linearity was generally looked upon as more of
a curse than a “feature”, the advent of digital systems that operate in a completely
linear fashion has made many appreciate the quirks of non-linear audio processing.
Unlike linear designs, non-linear devices require the user to actively experiment
with gain staging to find the “sweet spot” of the circuit. Although this requires a
small amount of effort on part of the engineer, if used properly, the effect can add a
dynamic aspect to performances that can enhance the impact of a song.
The non-linearity in the 542’s “True Tape” circuitry and Saturation control
necessitate taking note of both drive and input levels. How levels are staged into