Packet transmission of speech using variable-quality coding and time-interval modification

Abstract

Speech transmission by switched digital packets provides opportunities for increased utilization of transmission capacity. We describe a combination of processing features designed to maximally load a transmission facility and accommodate fluctuating demands on it. Our system detects individual speech energy bursts and, in effect, discards the silent intervals between bursts. It digitally encodes each burst with a quality (bit rate) that reflects serve demands being made on the transmission facility at the moment. In a preliminary study of these features, we find that elimination of within-sentence silent intervals saves about 20% of the total sentence time. We also find that digital coding (by ADPCM) in the range 40–20 Kbits/sec provides useful quality variation. We suggest that these flexibilities and modest buffer storage can aid utilization of transmission capacity.