Vesa Ruoppila

Genetic annealing search for index assignment in vector quantization

Abstract A Genetic Annealing Algorithm (GAA) has been applied to an Index Assignment (IA) problem in Vector Quantization (VQ). The proposed combination of annealing, selection and recombination mechanisms is new and possesses an advantage with regard to an implementation on a single processor machine for the reason of satisfactory performance when using a reasonably small population. The assessment of the proposed method by using a vector quantization of Line Spectrum Frequencies (LSF) of a speech coder, the experiments with the vector quantizers trained on the Gaussian data as well as the tests on the Quadratic Assignment Problem (QAP) benchmarks are presented.

Signal modification method for variable bit rate wide-band speech coding

This paper introduces a novel signal modification method for wide-band code-excited linear prediction (CELP) speech codecs to improve pitch prediction at low bit rates. The method is enabled only in stable voiced speech frames, and preserves the original time scale at the end of each frame. This feature helps to avoid artifacts and simplifies an encoder implementation. The signal modification includes a classification algorithm as an integral part. The classification algorithm detects the frames most suitable for signal modification and low bit rate coding, and can be employed in a rate selection module of variable bit rate (VBR) codecs. In this paper, the signal modification method is applied in an experimental VBR wide-band speech codec derived from the 3GPP adaptive multirate wideband (AMR-WB) standard (ITU-T Recommendation G.722.2). The codec fulfills the system requirements of IS-95/CDMA2000 Rate Set II, operating at source coding bit rates 12.65, 6.2, and 1.0 kb/s. The signal modification is used in the 6.2 kb/s mode dedicated for voiced speech frames. Listening test results demonstrate the good performance of the proposed method. The signal modification method is used in the Nokia/VoiceAge codec that was declared in April 2003 as the winner of the selection phase in the 3GPP2 CDMA2000 wide-band speech codec standardization.