Post war report on the German Tonschreiber b

(wartime magnetic tape recorder, 1944) (AEG - Telefunken)
(pdf)
Consider also: “Exhibits”

Magnetic tape recorders seemed, virtually, to be unknown in Anglo-Saxon countries (1944/45). Reading allied post war reports on this subject, one gets the impression that their sound engineers had been very delighted by this new technology.

Although, recorder type b had not yet been fit with RF wiping and recording bias (only used, since 1941, by the German broadcast organisations, RRG), it employed DC bias instead; its performance at 72 cm/s tape speed showed, however, a rather flat response between < 100 Hz up to 8000 Hz. (consider the report for more details)

RF bias enhanced the tape recorder performance enormously and allowed audio dynamics up to 60 dB (shellac records reached maximally 40 dB). German broadcast tape recordings could cover frequencies > 12 - 15 kHz. Even several stereo broadcast recordings have survived (1943/44).

The recorder type b was designed as to cover variable tape speeds from 9 cm/s up to 120 cm/s. The capstan rotation was controlled by means of a synchronous motor system, which was powered by means of an adjustable frequency (20 watts). That has to be, for example, 22 Hz at a tape speed of 9 cm/s and for 120 cm/s they utilized 292 Hz.

Very special was the ingeniously designed rotatable multi head device (4 heads), which allowed the increase of the audio pitch, whereas the tape speed had been reduced up to a factor 4. When listening to spoken sound (content) by decreased tape speed, the audio spectrum, however, becomes like “Donald Duck”sound, although its content is still quite well intelligible.

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