Electrical circuits for the production of subjective auditory effects

摘要

649,709. Transmission systems. STANDARD TELEPHONES & CABLES, Ltd. March 21, 1947, No. 7818. Convention date, July 30, 1940. [Class 40 (iv)] To produce the impression of a wide band transmission whilst transmitting only a narrow band of frequencies the original signal is distorted by means of a non-linear device such as a grid-leak detector T1 (Fig. 1) and the distorted signal is transmitted to a low-pass filter F2 through a frequency-selecting and phase-shifting network L1, C3, R5 which is so arranged that its characteristic is varied at about 7 c.p.s. The filter F2 has a cut-off at 3,000 c.p.s. The distorted signal may be combined with an undistorted signal in a mixer T2 before the transmission is filtered. The frequencies picked up by the microphone M1 are amplified at A1 and are fed partly over a direct channel to the mixing valve T2 and partly through a high-pass filter F1 (cut-off 1000 cycles) to the detector T1. The output impedance of a reactance valve T3 is included in the parallel tuned circuit L1, C3, R5 so that the tuning may be varied periodically under the control of an oscillator O1 Modifications. The Specification describes various means for producing harmonics and changes in phase. Dry rectifiers, diodes, anode bend detectors or grid-leak detectors may be used as the non-linear device. The cyclic variation in the phase-shifting may be controlled thermionically as in Fig. 1 or mechanically as in Fig. 5. In the arrangement shown in Fig. 5, the middle and lower frequeiicies are picked up by a microphone M2 and are fed to the mixing valve T2. The highfrequencies picked up by microphone M1 are amplified at B1 and rectified by diodes T8, T9. The rectified output of T8, T9 is applied through a reactance valve T7 to a beat frequency oscillator 03 so as to frequency-modulate the output thereof. A reactance valve T6 and a beat frequency oscillator 02 constitute a second stage of frequency-modulation to which is connected a grid-leak detector T1. The output from T1 is fed to the mixing valve T2 over a phase-shifting network comprising a resistance R5, an inductance L1 and a motordriven condenser C3. In another arrangement, Fig. 7, distortion is produced by a grid-leak detector T4 and the phase-shift is controlled by a voltage fed back to the grid of T10 about 90 degrees in advance of the plate voltage. The valve acts as a variable inductance in parallel with L1 of the tuned circuit L1, C3.