Patent GB-1351804-A (GB)
Title: Method and apparatus for picking up sounds
IPC: G11B5/00
Filed: 1971-04-19
Abstract: 1351804 Microphone systems; stereophonic systems; loud-speaker systems D S GOLDSMITH 19 April 1971 [19 Feb 1970] 21764/71 Headings H4R and H4J [Also in Divisions G5 and G3] Microphone system.-A microphone array "A" (Fig. 1) in a sound studio comprises four pairs of microphones 56, 56<SP>1</SP>, 57, 57<SP>1</SP>, 58, 58<SP>1</SP>, 59, 59<SP>1</SP> (Figs. 6, 10). Each pair, such as 56, 561 is contained within one quarter of a four vaned baffle. A dummy head 110 (Fig. 4) has microphones for binary pick-up. The microphone array can be moved parallel to a beam 15 (Fig. 1) in direction 21 under control of a motor 28 (Fig. 4) and in a direction 37 perpendicular to direction 21 under control of a second motor. The microphones 56 to 59<SP>1</SP> are rotatably mounted about their vertical axes. Arms 69, 70 (Fig. 4) engage friction bands 72, 73 on opposite sides of the vertical axis of microphones 56, 56<SP>1</SP>. A servomotor 78 has a friction wheel which engages a cross arm connected to arms 69, 70. Operation of servomotor 78 causes microphones 56, 56<SP>1</SP> to rotate in opposite directions about their common vertical axis and in similar manner causes microphones 59, 59<SP>1</SP> to rotate in opposite directions about their common vertical axis. A servomotor 82 effects rotation of microphones 57, 57<SP>1</SP> and 58, 58<SP>1</SP> in analogous manner. The servomotors are under control of a synchrocontroller 145 (Fig. 4) associated with motor 28. The baffle has active sound absorbers 52a. An alternative, interchangeable, microphone assembly (Fig. 14, not shown) has eight microphones equally spaced about the exterior cylindrical surface of a baffle assembly (195). The interior of the cylinder is padded and includes a cylindrical core 48a. The padding surrounds four spaced apart sound absorbers (198). A dummy head is also provided. The microphones (Fig. 1 or Fig. 14) pick up sounds from musicians or from loud-speakers. Microphone circuits.-The output of microphones 56, 57<SP>1</SP> are supplied to amplifier 114 (Fig. 10). Similarly the outputs of microphones 57, 59<SP>1</SP> are supplied to amplifier 115, microphones 56<SP>1</SP>, 58 are supplied to amplifier 116 and microphones 58<SP>1</SP>, 59 are supplied to amplifier 117. Units 118 to 121 comprise compressors, equalizers and filters and are connected to gain controls 122 to 125, these in turn being connected to further amplifiers 126 to 129. The microphones are of condenser type and have five conductors extending to a power supply 113 via slip rings. Slip rings also connect to the dummy head 110. The power supply 113 acts to control the directional characteristics of the microphones. Movement of the microphone system by the motors, &c., is under control of a numerical control system provided with programme information stored on magnetic tape, punched cards or punched tape. The movements and responses of the microphones not only follow positional and other sequences set up in the programme but also follow the programme at the same rate at which the music is being played. A differential 157 (Fig. 10) compares the rotational position of the baffle, derived from a displacement transducer 158, with a desired position signal emanating from a reader 160. The output of differential 157 is an error signal which is amplified by a servoamplifier 156 and fed to a servomotor 50 (see Fig. 4) which causes rotation of the drive shaft 48 of the baffle to reposition the baffle. Velocity stability is provided by a tachometer-generator 155 mounted on a shaft common to the servomotor 50. A Y-axis differential amplifier 150 has a servoamplifier 149 for the signal generated thereby, which controls a torquer 42 driving a shaft 40 for translating the baffle in respect of the Y-axis. A position transducer 151 creates a signal representing the instantaneous position of the baffle relative to the Y-axis. A tachogenerator 148 feeds back a signal proportional to baffle translational velocity to the servoamplifier 149, thereby forming a closed loop. Desired declination of the microphones may be carried out by position transducer 151 or by a reduction drive 154 operatively associated with a synchrotransmitter 153 the output of which is fed to servomotor 82 which properly positions one set of microphone pairs. Similar control for the X- axis is provided in the form of a differential amplifier 144 and an amplifier 141 having a feedback generator 140 serving to drive motor 28 to cause rotation of shaft 24. A reduction drive 146 operates a synchro-transmitter for declinating the other set of microphone pairs in relation to the X-axis. The reader 160 controls reverberation through a control knob 131 which acts upon reverberation units 112a to 112d. The reader 160 controls microphone directionality by an output supplied to a differential amplifier 113d which compares the command signal emanating from the reader 160 with the output of the position transducer 113e which senses the position of the polarizing voltage control 113a of the microphone power supply 113. The position of the voltage control is moved by servomotor 113b which receives a signal from differential amplifier 113d through servoamplifier 113c. Reader 160 may be a magnetic numerical control tape reader, speed control being provided by a speed controller using implicit digital information input. Alternatively, numerical control may be analog, digital (with or without external interpolation), digital incremental, digital positional or analogue positional. Other control systems include a digital incremental pulse count system using constant feedback servos and an analogue interpolating variable feedrate system. Pacing system.-A stepping switch 163 determines which tone detector or bank of tone detectors 137 is to be energized for subsequent actuation upon "hearing" the frequency to which it is responsive. Switch 163 is programmed by a matrix switchboard or plugboard. Assuming a characteristic tone to be played by the musicians, detector 137 emits a signal which is received by a relay which de-energizes a timing motor 164, causing a synchro-transmitter to cease rotation and occupy an angular position proportional to the time between motor 164 being energized and the tone being played. If the tone is not received at the correct time the synchro transmitter will be positioned either clockwise or anticlockwise of a given reference position. Characteristics are carefully selected to avoid ambiguity. If the performance is beyond the tolerance of the pacing system, the control system is shut off. Alternatively, instead of being paced, the control system may be shut off if a desired tempo is not maintained. In place of the tone detectors 127, a continuously tunable band pass filter may be used, adjusted to a desired response frequency just prior to the expected time at which such frequency is expected to occur in playing. Potentiometers, mixers or volume or signal control devices may be provided to make a sound image move from one loud-speaker to another. The controls may be programmed, e.g. paced, in accordance with the tempo of the composition. Speaker system.-A binaural speaker system (Fig. 18) has left and right speakers 326, 324 each with its axis directed upwards and with a headrest in between. An adjustable delay line unit 308 and volume control 309 connect to a composite audio line 303.