Audio signal processor

Abstract

NTSC signals have a frame rate of 29.97 frames per second. In SDI, audio data is sampled at a rate 30n where n is an integer, e.g. 48K samples per second. Thus there are 1601.6 samples per frame. Although there are an integer number 8008 samples per five frame sequence, two frames have 1601 samples and 3 frames have 1602 samples. This creates a variable storage requirements from frame to frame and causes problems in editing. The SDI audio data is separated from associated video and decimated by a factor h, where h=4 for example in a signal processor 2, 3, 4, 5 and 6. The decimated data is written into a FIFO circuit at the rate 30n/h synchronously with frame timing under the control of a frame reference generator 10, 9. A fixed integer number n/h of samples is written into the FIFO 7 in each frame under the control of a write control circuit 8. n/h=400 for example, where n=1600 and h=4. Any additional sample in each frame is dropped. The 400 sample frames are stored on a disc 14. If it is desired to reproduce the samples, they are written into a FIFO 12. A read control circuit 13 reads the samples out synchronously with the video frame rate. In three frames 400 samples are read out: in two frames 401 samples are read out.