Professional-Use PCM Audio Processor with a High Efficiency Error Correction System
A digital signal processor for professional use 2-channel PCM (Pulse Code Modulation) recording system utilizing 3/4-in cartridge type VTRs will be described in this paper. The basic system consists of the processor, two VTRs, and editor, and a delay unit. To ensure its professional-use quality, a powerful coding system of 16-bit linear quantization having ample correctability against transmission errors and flexible editing capability is applied. The transmission bit-rate is kept low well within the capacity of 3/4-in VTR, furthermore, the coding is devised to enable a stable timing control of data input and output. As a result, the processor is practically fault-free of error correction. For editing recorded tapes, an electronic editing is inevitable for various reasons, VTR's herical-scan format being one of them. The authors have designed two types of electronic editing methods on this system. One is "simple editing" which combines two digital signal flows reproduced from two VTRs by switching between the two at a rate of pseudo-TV frame (approximately 33m sec per frame unit). In this editing, some discontinuity of the decoded waveform is admitted. The other is the "high precision editing" defined by authors, for which an electronic editing unit has been newly developed. The unit smooths out such waveform discontinuity by providing each signal flow with appropriate weighting done digitally.
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