BBN Technologies

Noise-robust voice coding (a/k/a vocoding) at data transmission rates well under 1000 bits/second is a very challenging problem with a high payoff. Military, police, fire and other emergency personnel frequently must communicate in harsh acoustic noise environments using limited-capacity radio transmission links. BBN's very low data rate Noise Robust Vocoder (NRV) technology is designed to produce a clear, highly-intelligible, speech signal in such harsh environments while using only a small fraction of the available transmission capacity. As a result, our NRV technology conveys critical information with greater clarity than standard higher-rate vocoders while enabling more simultaneous conversations over the same limited-capacity channels.

In 2006, BBN passed a major ASE program milestone by demonstrating an 800 bps NRV with performance superior to that of the current 2400 bps NATO-standard vocoder, STANAG 4591 (also known as MELPe). As described in BBN Report 8452, this 800 bps NRV uses an advanced signal processing technology, known as Spectral Hypothesis Testing, to jointly estimate speech parameter trajectories over a block of multiple speech frames. As seen in the figure above, formal subjective tests of speech intelligibility demonstrate that the 800 bps NRV significantly outperforms 2400 bps MELPe in each of four harsh military noise environments, as well as in a quiet environment. BBN continues to improve this technology with a goal of outperforming 2400 bps MELPe in harsh acoustic noise environments at a data rate of only 300 bps.