Adaptive Multi-rate Wideband Speech Codec Based on CELP Algorithm: Architectural Study, Implementation & Performance Analysis

This paper investigates application of Code Excited Linear Prediction algorithm on Adaptive Multi Rate Wideband coder. The proposed coder can adaptively change its bit-rate based on C/I ratio depending on channel conditions. The coder has nine bit-rates from 6.6 kbps to 23.85 kbps. An e-test bench using MATLAB is created to implement proposed coder and series of simulations are carried out to judge the performance of implemented coder using Subjective and Objective analysis. Simulation results clearly advocate that it is possible to produce variable bit rate (by tuning to channel conditions) in CELP coder by affecting coefficients of coder while still maintaining comparable speech quality with reference to AMR WB coder standardized by 3GPP and ITU-T [5]. It is also evident from the simulation results that Signal to Noise Ratio (SNR), Segmented SNR, Perceptual Evaluation of Speech Quality (PESQ) and Mean Opinion Score (MOS) increases with increase in bit rates of proposed coder and Absolute Error (Abs Err), Mean Square Error (MSE), Root Mean Square Error (RMSE) reduces with increase in bitrates.