Efficient and scalable parametric stereo coding for low bitrate audio coding applications

Abstract

The present invention provides improvements to prior art audio codecs that generate a stereo-illusion through post-processing of a received mono signal. These improvements are accomplished by extraction of stereo-image describing parameters at the encoder side, which are transmitted and subsequently used for control of a stereo generator at the decoder side. Furthermore, the invention bridges the gap between simple pseudo-stereo methods, and current methods of true stereo-coding, by using a new form of parametric stereo coding. A stereo-balance parameter is introduced, which enables more advanced stereo modes, and in addition forms the basis of a new method of stereo-coding of spectral envelopes, of particular use in systems where guided HFR (High Frequency Reconstruction) is employed. As a special case, the application of this stereo-coding scheme in scalable HFR-based codecs is described.

1 . A decoder for decoding a bit stream, the decoder comprising:
 a lowband core decoder for producing a lowband output signal, the lowband output signal having a lowband mono signal or a lowband stereo signal, wherein the lowband core decoder is configured for receiving an encoded lowband signal included in the bit stream; and   a high-frequency reconstruction unit for generating a synthetic highband using the lowband output signal and for adjusting the synthetic highband according to a level parameter included in the bit stream to obtain a highband and for combining the highband and the lowband output signal.   
     
     
         2 . Method of decoding a bit stream, comprising:
 producing a lowband output signal, by a core decoder, the lowband output signal having a lowband mono signal or a lowband stereo signal, wherein the lowband core decoder is configured for receiving an encoded lowband signal included in the bit stream;   generating a synthetic highband using the lowband output signal;   adjusting the synthetic highband according to a level parameter included in the bit stream to obtain a highband; and   combining the highband and the lowband output signal.   
     
     
         3 . Non-transitory storage medium having stored thereon a computer program for performing a method of decoding a bit stream, comprising:
 producing a lowband output signal, by a core decoder, the lowband output signal having a lowband mono signal or a lowband stereo signal, wherein the lowband core decoder is configured for receiving an encoded lowband signal included in the bit stream;   generating a synthetic highband using the lowband output signal;   adjusting the synthetic highband according to a level parameter included in the bit stream to obtain a highband; and   combining the highband and the lowband output signal.