| 摘要 |
1282641 Speech encoding T PATTERSON 14 May 1970 [14 May 1969] 24525/69 Headings H4R and R22X In a device for encoding an electrical waveform e.g. a speech waveform, time intervals between successive occurrences of predetermined amplitudes are measured and non-linear digital outputs indicative of the length of said time intervals are then determined. A speech signal which may have been squared off in a clipper circuit together with the output from a clock 621 is incident on the first stage 601 of a dual shift register 600. The reverse unit 611 always indicates the opposite of 601. The length of the pulses are measured in the following manner. When a 1 reaches unit 610 in the shift register 600 and units 633, 632 &c. are triggered, starting at 633 to pass all the consecutive 1 units from shift register 600 to shift register 656 by means of the AND gates 624 to 633, in such a way that a non-linear companding characteristic is attained. Thus if the bottom four units 607 to 610 of shift register 600 register "1"s only the bottom three units of shift register 656 register "1"s. The stored values on shift register 656 are then fed back via the parallel output of shift register 656 to shift register 600, so that now only the end three units 608 to 610 carry "1"s. The same procedure is repeated for the left hand side of the apparatus to encode the "0"s on the units 611 to 620 of shift register 600. The values in shift register 600 are read out in sequence to control the subsequent switching of the circuit. Under the action of logic units shift registers 656 and 670, are read out in turn via an adder unit 667 to provide a series of equi-weighted pulses representing the input signal. A de-coder unit, Fig. 2, receives the input chain of pulses from a dual shift register 111. These pulses are then fed via units 140 to 149 to a shift register comprising bi-stables 160 to 169. These feed in parallel a digital to analogue converter 117 which produces a voltage output whose value is proportional to the duration of the original encoded pulses. This voltage is fed to a unit 118 which inverts a high voltage into a low voltage and vice versa so that the voltage is now proportional to frequency. The frequency proportional voltage is then used to control the bandpass characteristic of a filter 181. The left hand half of the apparatus operates in a similar manner. The two signals control filter 181 in turn. The output of shift register 111 is then pulsed out by the clock 112 and through the filter, to produce a representation in analogue form of the input. In another embodiment the variable frequency filter 181 is replaced by a series of separate filters. The value of the duration of the signal as indicated on shift register 160 to 169 is then used to control the switches so that only one filter is connected at a time. The contents of shift register 111 is then fed through the filter unit in serial form. |
