Digital Voice Storage in a Microprocessor

We describe digital encoding and automatic silenceediting techniques for PCM and ADPCM voice storage in the MC68000 microprocessor. We give program details for encoding, silence elimination, storage of active speech bursts and reconstitution of the signal upon read-back. Coding rates in the range 64 down to 16 kbits/s are implemented. We find that silent intervals corresponding, typically, to 20-40 percent of the duration of continuous input speech can be usefully eliminated. Available storage is thereby used more efficiently. The eliminated intervals are automatically reinserted upon read-back. We further demonstrate automatic scaling of the silent intervals in the reconstituted output. We confirm that a variation of ± 50 percent in the reinserted silent intervals is typically acceptable. This latitude can significantly alleviate buffer requirements in a packet transmission system for voice.