A Fixed Rate Speech Coder Based on the Filter Bank Method and the Inflection Point Detection

Abstract

A fixed rate speech coder based on the filter bank and the non-uniform sampling technique is proposed. The non-uniform sampling is achieved by the detection of inflection points (IPs). A speech block is band passed by the filter bank, and the subband signals are processed by the IP detector, and the detected IP patterns are compared with entries of the IP database. For each subband signal, the address of the closest member of the database and the energy of the IP pattern are transmitted through channel. In the receiver, the decoder recovers the subband signals using the received addresses and the energy information, and reconstructs the speech via the filter bank summation. As results, the coder shows fixed data rate contrary to the existing speech coders based on the non-uniform sampling. Through computer simulation, the usefulness of the proposed technique is confirmed. The signal-to-noise ratio (SNR) performance of the proposed method is comparable to that of the uniform sampled pulse code modulation (PCM) below 20 kbps data rate.

A Fixed Rate Speech Coder with Improved Database Search

“…By sampling irregularly at inflection points, a smaller number of samples can be obtained compared to the conventional uniform sampling. As shown in Figure 1, the inflection points can be one of three types: local minima (point a), local maxima (point b), or points of simple slope change (point c) [7].…”

“…Speech coding techniques exploiting the non-uniform sampling have been studied widely [1][2][3][4][5][6][7]. Most of non-uniform sampling based speech coders show variable code rates which are not suitable for a fixed communication channel [1][2][3][4][5][6].…”

“…Most of non-uniform sampling based speech coders show variable code rates which are not suitable for a fixed communication channel [1][2][3][4][5][6]. Recently, a fixed rate speech coder based on the non-uniform sampling technique has been proposed in [7]. The speech coder uses the filter bank method and the inflection point (IP) detection technique.…”

“…The obtained IP pattern for each subband is compared with entries in IP pattern database, and the address of the closest pattern is transmitted through communication channel. In the receiver, the decoder fetches the IP pattern from the same database with the received addresses, and reconstructs the speech with interpolation and filter bank summation [7]. The obtained result shows acceptable quality of speech with the relatively low bit rate.…”

“…In this paper, several important speech parameters such as the Figure 1. Enlarged plot of a speech signal with various inflection points [7].…”