GB1021202A - Apparatus for recording and/or analysing electric and/or acoustic oscillations of various frequencies - Google Patents

Abstract

1,021,202. Recording music. I. SPONGA and H. J. EBERSTARK. Aug. 8, 1962 [Aug. 8, 1961], No. 30399/62. Heading G5X. [Also in Divisions A5, G1 and H3] Apparatus for graphical recording and/or analysing of electrical alternating current signals of various frequencies comprises plural electric wave filters tuned to a series of pass frequencies and having inputs arranged for connection to the output of a common amplifier fed with A.C. signals; plural electrical recording heads being coupled through rectifiers each to the output of one of such filters and an electroresponsive recording strip moved adjacently to the recording heads; each of which is actuated by a signal through its associated filter to produce a linear recording mark on the strip parallel to the direction of motion thereof to indicate frequency of the input signal by its lateral position amplitude by its intensity, and duration by its length. In Fig. 1 sounds are received by microphone 10 and are amplified to feed a set of parallel filters 12 having pass frequencies in an ascending series with frequency ratios 1: <SP>12</SP># 2 so that for sounds in the aural range the successive pass frequencies are spaced by one semitone pitch. The filter outputs are severally rectified to D.C. energization for a series of electrodes 20 spaced laterally across a uniformly moving recording strip 23 in opposition to a single common lower electrode 21; the strip being of paper impregnated with chemicals producing discoloration on passage of current between the electrodes of intensity dependent on the current amplitude. Alternatively the recording strips may be metallized paper or plastic film marked by burning of the metallization on passage of current between the electrodes. The several frequency components of the received sound are recorded as parallel interrupted lines on the recording strip; frequency or pitch being represented by lateral displacement, amplitude by intensity of marking and duration by length along the direction of motion of the strip, which may be marked with auxiliary lines corresponding to the several recording electrodes and to frequency or pitch (Fig. 2). Harmonic content of a single frequency received sound may be analysed by amplifying he input to the set of filters and removing herefrom the fundamental tone. The auxiliary lines may be more heavily marked on the recording strip where they correspond to the lines of the musical staff (Fig. 4). It is stated that key transposition may be achieved in recording by displacing the auxiliary lines relatively to the recorded traces, and that the auxiliary lines may be disposed to correspond e.g. to the keys of a piano or the unstopped strings of a guitar. A transparent template inscribed with the auxiliary lines appropriate to any stringed instrument may overly the recording strip. In a modification (Fig. 9) a pair of electrodes 100 may be applied e.g. to the brain of a subject and the resultant infrasonic potentials amplified to feed a frequency changer 101 (Fig. 10) whose output is applied to a range of filters 112 and rectifiers 113 feeding a recorder 18 as shown in Fig. 1. The frequency changer comprises a discriminator 103 producing a unidirectional voltage representing an input frequency f 1 , a proportion of which is derived from a variable potentiometer 104 to modulate at 105 a frequencyf 2 from a source 106 to yield a frequency f 3 , which is heterodyned by f 2 in converter 107 to give a frequency f 4 = f 3 - f 2 related' to f 1 by a constant ratio set by potentiometer 104. The output at 109 is derived from the output of converter 107 through variable-gain amplifier 108 controlled by rectification of the input voltage at 110, so that the output amplitude varies in correspondence with the input amplitude. In addition to brain potentials, muscular and cardiac potentials and the rate of respiration of a subject may be similarly recorded. Alternatively the recorded outputs of the several filters may be photo-electrically scanned to operate respective relays keying a range of corresponding audio oscillators whose frequencies are spaced in the ratio 1:<SP>12</SP># 2 feeding an amplifier and loud-speaker. Muscular, cardiac, and respiratory potentials may similarly be rendered audible. Structurally, the recording apparatus comprise (Fig. 11) a paper strip 23 winding from a delivery roll 40 over a conditioning roll 41 impregnating it with a current-sensitive reagent from a bath 43, and over a deflecting electrode roll 44, and guide table 45 to drive roll 46 rotated by motor and gear-box 47, speed adjustable by knob 50. Parallel electrode laminae 20 embedded in insulation 52 press the impregnated paper against electrode roll 44 and the electrode assembly to laterally traversable by leadscrew 53 and knob 44 e.g. for key transposition. Additional electrodes 55, 56 are respectively energized from a pulse generator to produce e.g. second time markings 57, and from a manually operated lever 59 applying a variable current, so that beat markings of variable stress may be applied at will. The electrode connections may be printed on an insulating sheet 60 and the panel 61 may carry controls 50, 54, 59; on/off switch 62, control 63 for the input amplifier (Fig. 9), control 64 for frequency multiplication factor (potentiometer 104 in Fig. 10) and selector switch 65 enabling the apparatus to operate to record physiological currents with frequency transposition, to record acoustical sounds without transposition, or to analyse harmonics of acoustical sounds.