GB1407196A - Apparatus for changing signal pitch - Google Patents

Abstract

1407196 Changing signal pitch BRITISH BROADCASTING CORP 3 Oct 1972 [16 Nov 1971] 53225/71 Heading H4R In apparatus for varying the pitch of a signal the signal is sampled, the samples fed into a store at a first rate and read out at a second rate, differing from the first with either the writing or reading process periodically caused to jump a predetermined number of stored samples. As described an audio signal is fed through an A to D converter 22 into a store 24 with the writing position in the store controlled by an address generator 32 and address switch 36. The signals are read out of the store under the control of read address generator 34 and address switch 36 and fed out via the D to A converter 40. The write address generator 32 and read address generator 34 are counters controlled, via the control logic 26, by the write clock signal 28 and read clock signal 30 and the counts of the generators 32 and 34 are continuously compared by jump logic circuit 38. When the counts in the two counters approach coincidence, which would entail reading a store as it was being written, the jump logic causes the read generator 34 to jump a number of storage position, either forwards, if the read out is slower than the write in, causing the read out to miss a portion of the signal, or backwards, if the read out is faster than the write in, causing the read out to repeat a portion of the input signal. In an alternative form the store can be recirculating a shift register, of digital or analogue form, with either a fixed input and a moving output tap or a fixed output and a moving input tap. Interpolations can be introduced to remove discontinuities during the jumps.