Jonas Svedberg

Quality evaluation of the G.EV-VBR speech codec

ITU-T has selected the candidate submitted by Ericsson, Nokia, Motorola, VoiceAge, and Texas Instruments as the baseline for the G.EV-VBR coding standard. G.EV-VBR is an embedded scalable speech codec that uses state-of-the-art technology to provide the most efficient encoded speech available for various real-time applications. EV-VBR encodes both narrowband (NB) and wideband (WB) speech signals starting at 8 kbps. Near perfect wideband representation is achieved at 32 kbps for all signal types. The bit stream is divided into five robust layers, providing sufficient granularity, in particular for VoIP applications. In addition, an extension to the codec will provide super- wideband and stereo capability by adding layers to the codec. Extensive listening tests were conducted during the ITU-T selection phase to support selection of the best- performing candidate. The selected EV-VBR candidate passed 69 of 70 required and 25 of 28 objective terms of reference.

MDCT audio coding with pulse vector quantizers

This paper describes a novel audio coding algorithm that is a building block in the recently standardized 3GPP EVS codec [1]. The presented scheme operates in the Modified Discrete Cosine Transform (MDCT) domain and deploys a Split-PVQ pulse coding quantizer, a noise-fill, and a gain control optimized for the quantizers properties. A complexity analysis in terms of WMOPS is presented to illustrate that the proposed Split-PVQ concept and dynamic range optimized MPVQ-indexing are suitable for real-time audio coding. Test results from formal MOS subjective evaluations and objective performance figures are presented to illustrate the competitiveness of the proposed algorithm.

A novel sinusoidal approach to audio signal frame loss concealment and its application in the new evs codec standard

The new 3GPP codec for Enhanced Voice Services (EVS) comprises a collection of frame loss concealment techniques, each specifically designed for the different coding modes of that codec. One of them, called “Phase Error Concealment Unit (Phase ECU)”, was developed for the High Quality (HQ) MDCT coding mode. Despite this target application, Phase ECU is a generic stand-alone tool operating on a buffer of the previously decoded and reconstructed time signal. Its framework is based on the sinusoidal analysis and synthesis paradigm. Besides a description of the basic technology we present optimizations and adaptations required for meeting the challenging 3GPP EVS codec performance requirements, and that make the method robust for a broad range of audio signals under various frame loss conditions from isolated frame erasures to severe burst loss. Test results are reported that show significant improvements over traditional techniques.

Harmonic Vector Quantization

Audio coding of harmonic signals is a challenging task for conventional MDCT coding schemes. In this paper we introduce a novel algorithm for improved transform coding of harmonic audio. The algorithm does not deploy the conventional scheme of splitting the input signal into a spectrum envelope and a residual, but models the spectral peak regions. The presented coding scheme is part of the recently standardized 3GPP EVS codec.