NOISE REDUCTION UNIT FOR VOCODER

Common description

NOISE REDUCTION UNIT (NRU) is designed for using with low bit rate vocoders 600-4400 bps. NRU makes noticeable positive effect for vocoder speech depending from noise type for input signal-to-noise ratios (SNR) 0…+20 dB.

Separation of speech and noises with overlapping spectrums is possible on the base of adaptive nonlinear processing in the frequency domain. The main discriminate sign between noise and speech is the time of spectrum stationarity. Suggesting that noise spectrum characteristics are changed slowly than speech spectrum characteristics.

Standard ITU-T P.862 PESQ-MOS criteria is used for output speech quality measurements

The maximum advantage of using proposed noise reduction algorithm is up to 6-8 dB of input SNR depending of noise type (car noise, street noise).

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Implementation

Noise reduction algorithm is implemented as fixed point C model for PC. It may be implemented in real-time on the base of TI's TMS320c54x/c55x DSP families under contract with resources no more than 20 MIPS and 10 Kwords of memory.

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Demonstration

Following speech files demonstrate the quality of NRU with RMELP vocoder 4400 bps:

Car noise, SNR +12 dB

Car noise, SNR +9 dB

Car noise, SNR +6 dB

Car noise, SNR +3 dB

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