Patent GB-1054241-A (GB)
IPC: G01V1/37
Abstract: 1,054,241. Correlation techniques. SEISMOGRAPH SERVICE (ENGLAND) Ltd. Nov.8, 1962 [Nov. 8, 1961], No.40018/61. Addition to 1, 029, 833. Heading G1U. [Also in Divisions G4 and G5] An apparatus for correlating two variables, one of which is represented by variations in an electrical signal, includes a recording head to which the electrical signal is supplied and a playback head, one of the heads providing an extended pattern of sensitivity distributed along a closed circular path and representing a function of the other variable. Relative movement is effected between this head and a recording medium round the circular path, so that an output is obtained from the playback head which represents a correlation of the variables. A suitable correlator utilizes a disc 20 formed from an oxide coated plastic sheet upon which the waveform to be processed is recorded in a number of tracks by the heads 17. The disc is secured to a driving member 23 which is driven by motor 26 in proximity with a circular board 14 of insulating material. This carries printed conducting tracks 16 which are in the form of the required reference waveforms with which the unknown waveform is to be correlated. The disc 20 is maintained in close contact with the board by gravity, increased air pressure above it &c. The outputs from the correlating heads may be passed to styli 33 and recorded on a rotating drum as at 32, or may be recorded in any other way. An alternative correlating arrangement is described utilizing a magnetic drum in place of the disc 20, the printed reference waveforms being supported on a flexible sheet which is fitted to the inside of a cylinder within which the drum rotates Figs. 2a, 2b, 2c (not shown). The printed circuit reference heads may be prepared photographically using galvanometric oscillograph techniques. Use of correlator as a spectrum analyser and filter. The reference heads take the form of a swept frequency, and taps may be connected along the track to enable different frequency sections of the waveform to be selected. Correlation outputs are derived when correlation is achieved between the input waveform to be analysed and a selected section of the reference waveform (whose bandwidth may be varied by means of the taps). The apparatus of Fig. 3 may be adapted for this purpose by having the printed reference waveforms as a series of waveform segments of increasing frequency, the ends of each segment being connected through the insulating board to metal segments which are contacted by brushes mounted on an insulating plate which is driven together with the magnetic record disc by a motor. The output across pairs of brushes is passed via slip rings to amplifiers (one for each of the tracks) which deliver a correlation output. By arranging that a number of parallel outputs are derived from different parts of the reference sweep waveform, spectrum analysis is carried out. Alternatively by using only one of the sets of tapped outputs, filtering of an input signal may be achieved. By connecting shorting links or resistors between taps, any complex type of filtering may be performed. Speech recognition. The reference tracks on the drum or disc correlator may represent the 40 phonetic units (phonemes) of speech. Incoming speech waveforms are correlated with these reference waveforms, and the output is processed according to the type of phoneme being detected by a particular track, the presence of a particular phoneme ultimately being indicated by a pulse on a corresponding line. The outputs may be used to operate a typewriter, coder or other device.