A fast algebraic codebook search method based on iteration-free pulse replacement is proposed. The method comprises two stages. At the first stage, an initial codevector is determined by the pulse-position likelihood-estimate vector. At the second stage, after computing pulse-contributions for every track, the pulse replacement is performed to maximise the search criterion over all combinations, replacing the pulses of the initial codevector with the most important pulses for every track. Experimental results show that the proposed method is very efficient in terms of computational complexity and speech quality compared to previous pulse replacement methods.

Iteration-free pulse replacement method for algebraic codebook search

An efficient method for codebook search, employed in speech coding, uses an optimal pulse-position grouping and a split track arrangement, based on a likelihood estimator. Also disclosed are codecs, mobile voice communication devices, telecommunications equipment and telecommunications methods.

Apparatus, methods and articles incorporating a fast algebraic codebook search technique

The present research can decrease the amount of computation and enhance speech quality by using a global pulse replacement method in a fixed codebook search. The fixed codebook search method in a speech encoder based upon global pulse replacement, includes the steps of: (a) computing absolute values of the pulse-position likelihood-estimator vectors; (b) temporarily obtaining a codebook vector; (c) computing a mathematical equation by replacing a pulse; (d) determining whether a value computed based upon the mathematical equation is increased after pulse replacement; (e) obtaining a new codebook vector by replacing the pulse; and (f) maintaining a previous codebook vector.

Method for searching fixed codebook based upon global pulse replacement

There are several sub-optimal search techniques for fast algebraic codebook search of ACELP speech codecs. Focused search method, depth-first tree search method and pulse replacement methods are used to reduce computational complexity of algebraic codebook search. In previous pulse replacement methods, the computational load is increased as the pulse replacement procedure is repeated. In this paper, we propose a fast algebraic codebook search method based on iteration-free pulse replacement. The proposed method is composed of two stages. At the first stage, an initial codevector is determined by the backward filtered target vector or the pulse-position likelihood-estimate vector. At the second stage, after computing pulse contributions for every track the pulse replacement is performed to maximize the search criterion Qk over all combination replacing the pulses of the initial codevector with the most important pulses for every track. The performance of the proposed algebraic codebook search method is measured in terms of the segmental signal to noise ratio (SNRseg) and PESQ (Perceptual Evaluation of Speech Quality) using various speech data. Experimental results show that the proposed method is very efficient in computational complexity and speech quality comparing to previous pulse replacement methods.

Efficient fixed codebook search method for ACELP speech codecs

In this paper, we examine the impact of four voice over long term evolution adaptive multi-rate wideband codec mode-sets on coverage at pedestrian and vehicular speeds Industry-standardized mean opinion scores were used as a metric for voice quality Controlled laboratory experiments simulating pedestrian speeds indicated that there was an improvement in voice quality when mode-set eight was employed At vehicular speeds, mode-set eight outperformed the other mode-sets for path losses less than 130 dB; however, all four mode-sets experienced a significant decline in voice quality when the path loss was greater than 130 dB Based on the current implementations, there are no significant benefits to lowering the mode-sets or deploying dynamic codec rate adaptation

A Comparative Study of Voice Quality and Coverage for Voice over Long Term Evolution Calls Using Different Codec Mode-sets

Speech codecs with ACELP structure are widely used due to their high performance for the bit rates between 4 kbps and 16 kbps. In ACELP codecs, the search for the best code vector from a huge codebook is the crucial part in both performance and complexity. In most cases, a non-optimal search method is used in order to reduce the search load with minimal performance degradation. However, its complexity is still the major part of the overall codec complexity. Furthermore, there is no unified method for ACELP codebook search; a rather different method is developed for each ACELP codec. In this paper, a unified framework for the efficient ACELP codebook search method based on the pulse replacement procedure is proposed, and is applied to standard ACELP codecs. It is confirmed that the proposed method provides the same performance as the standard method with much less search load.

Hochong Park

Papers

Efficient codebook search method for ACELP speech codecs