GB1286487A - Speech unscrambler - Google Patents

Abstract

1286487 Speech frequency converter WESTINGHOUSE ELECTRIC CORP 3 Sept 1969 [23 Sept 1968] 43654/69 Heading H4R In apparatus for converting "helium speech" to a more intelligible form the speech is converted to digital form and fed into a storage device at a first rate and removed from the store at a second, slower, rate and converted back to analogue form. When the store is filled, due to the slower rate of removal than filling, filling is discontinued, so that some speech is lost, until the store is effectively empty again. Fig. 2 shows a system for treating speech from a diver in an helium atmosphere in which the fundamental frequencies, i.e. the pitch frequencies, are transmitted unchanged, while higher frequencies in the region of the first, second and third formants are fed, via an a to d converter 29, to the storage device 37, from which they are removed at a slower rate, via the d to A converter 40, an amplifier, and smoothing filter 45, to be recombined with the lower frequencies at adder 50. Fig. 3 shows the storage apparatus which comprises similar shift register stores 60, 61 ... for each digit of a multi-digit coded sample. The stores are loaded under the control of a load counter 72 fed from a clock 70 and read out under the control of unload counter 76 fed also by the clock 70. The two counters are set to counts providing the appropriate load to read out frequency ratio to provide the required shift in speech frequencies. Each time the load counter signals a load operation a counter 80 is advanced one count while reading out steps the counter back one count. When the counter reaches such a count as indicates that all the stages of the store are filled with unread samples, an output on line 81 inhibits the input to the load counter 72 so that no more samples are fed into the store until the store is effectively empty, i.e. filled with samples each of which has been read out, as indicated by the up down counter 80 being counted back to zero. Normally signals in the stores are recirculated and read out in the order that they were inserted. The clock rate and counters are arranged so that the load counter controls the feeding in of a new value to the store in the position occupied by the oldest sample which is inhibited from recirculating by a connection via gate 85 in the store.