GB974332A - Improvements in and relating to apparatus for audio-vocal conditioning and to a method and apparatus for modifying the acoustic properties of a room - Google Patents

Abstract

974,332. Voice training equipment. SOC. CIVILE D'ETUDES ET DE BREVETS MOTA. Feb. 14, 1961 [Feb. 15, 1960 (4)], No. 5494/61. Heading H4J. In apparatus for use in speech training and for modifying the effective acoustic properties of a room, sound signals from a microphone 3 are transmitted to headphones 40 over one of two channels 10, 20. The intensity of the signals is detected by a circuit 30 which opens channel 10 when the intensity (signal 50, Fig. 2), falls below a critical value I 0 , and opens channel 20 when the intensity (signal 52) rises above the critical value only one channel being open at any time. Channel 10 includes a filter 13 accepting mainly low frequencies (pass characteristic E 1 , Fig. 2). Channel 20 includes a filter 23 accepting mainly high frequencies (pass characteristic E 2 ). A switch 28 enables different filters 26, 27 to be substituted for filter 23. The intensity of the microphone signals is indicated by a meter 42. The complete circuit of Fig. 1 is illustrated in Fig. 3 (not shown). Microphone circuit 1.-The microphone 3 is followed by a pre-amplifier 4, a volume control 5 and an amplifier 6. The circuit 1 is linked to channels 10, 20 by an impedance matching amplifier 7. Channels 10, 20.-Volume controls 11, 21 control the signals applied to amplifiers 12, 22. Adjustable filters 13, 23 and gates 15, 25 pass the signals to the output stage 2. The auxiliary channel 30 opens gates 15, 25 only one at a time. Auxiliary channel 30.-A volume control 31 and an amplifier 32 feed the signal from the microphone circuit 1 to a detector 33 which controls a thermionic flip-flop 35 in accordance with the intensity of the signal. Gate 15 opens for signals of low intensity and gate 25 opens for signals of high intensity. The time constant of the flip-flop is controlled by a device 34. The time T 1 taken for the flip-flop to switch over from open channel 10 to channel 20 is longer than the time T 2 taken to switch back. Output circuit.-The two channels 10, 20 are linked to headphones 40 by an amplifier 8 and a volume control 9. In an alternative output arrangement, Fig. 10, one earphone 73 is connected to the channels 10, 20, as before and the other earphone 63 is connected in channel 10 before the gate 15. Loud-speakers may be used instead of earphones (Fig. 11, not shown), in order to control the effective acoustic properties of a room.