A frequency domain noise cancelling preprocessor for narrowband speech communications systems

Performance of narrowband speech communications systems, such as Linear Predictive Coding (LPC), is often severely degraded by the presence of ambient acoustic noise in the input speech signal. Spectral subtraction techniques show promise in improving the overall performance of LPC in acoustic noise environments, but typically present annoying musical tones at the output. A spectral subtraction technique is described, which includes a biased estimate of the noise, that does not present musical tones at the output. In addition, an automatic speech activity detector is described and used to adapt the noise estimate to changing noise environments.