Robust MELP vocoder 4400 bps

Common description

Robust MELP vocoder with rate 4400 bit/s (RMELP 4400 bps) is intended for using in discrete channels with bit error rates (BER) up to 7-9%.

Robust MELP vocoder is built on the base of low bit rate MELP vocoder and original channel coding scheme using codes with high bit error correction capability.

Low bit rate MELP (Mixed Excitation Linear Prediction) speech coders use classical parametric model of description of speech signals. This model is implemented on the base of linear prediction filter with mixed excitation in several frequency bands.

Independent estimation of voiced/unvoiced decision in different frequency bands is providing more natural synthetic speech sounding then quality of classical LPC vocoders with binary voiced/unvoiced decision for single band.

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Implementation

RMELP 4400 bps is implemented as fixed-point ANSI-C models for PC. It also has real-time implementations on the base of TMS320c54x/c55x DSP families.

DSP implementations have following features:

• C call interface for top level procedures
• real time work
• multichannel support - independent processing of several duplex channels on single DSP
• code compatibility within DSP family
• high optimization of program code - all internal signal processing procedures are implemented on assembler language

Parameters of RMELP 4400 bps TMS320C55x implementation:

N – number of channels

Parameters of RMELP 4400 bps TMS320C54x implementation will be sent on demand. Please ask.

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Speech samples

Here you can test speech quality of following speech samples of RMELP 4400 bps vocoder with different channel bit error rates (BER) with or without error bit grouping. (In case of modeling of error bit grouping we use 2 state Hilbert model with BER probability and PGB probability that mean probability of transition channel from "good" state to "bad" state and vice versa.)

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