Efficient and scalable parametric stereo coding for low bitrate audio coding applications
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:
an input interface for receiving the bit stream comprising an encoded stereo signal having two channels, the stereo signal having a set of frequency bands, balance parameters for each frequency band, and level parameters for each frequency band, a level parameter representing a total power of the two channels for a frequency band;
a converter for converting the balance parameters and the level parameters into power values of the first channel for each frequency band and power values of the second channel for each frequency band;
a lowband core decoder for producing a lowband output signal, the lowband output signal having a lowband stereo signal, wherein the lowband core decoder is configured for receiving the encoded stereo signal having two channels included in the bit stream; and
a high-frequency reconstruction unit for generating a synthetic highband signal using the lowband output signal and for adjusting the synthetic highband signal according to the power values of the first channel for each frequency band and the power values of the second channel for each frequency band to obtain an adjusted highband signal and for combining the adjusted highband signal and the lowband output signal.
2. Method of decoding a bit stream, comprising:
receiving the bit stream comprising an encoded stereo signal having two channels, the stereo signal having a set of frequency bands, balance parameters for each frequency band, and level parameters for each frequency band, a level parameter representing a total power of the two channels for a frequency band;
converting the balance parameters and the level parameters into power values of the first channel for each frequency band and power values of the second channel for each frequency band;
producing a lowband output signal, the lowband output signal having a lowband stereo signal, wherein the producing comprises receiving the encoded stereo signal having two channels included in the bit stream;
generating a synthetic highband signal using the lowband output signal;
adjusting the synthetic highband signal according to the power values of the first channel for each frequency band and the power values of the second channel for each frequency band to obtain an adjusted highband signal; and
combining the adjusted highband signal 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:
receiving the bit stream comprising an encoded stereo signal having two channels, the stereo signal having a set of frequency bands, balance parameters for each frequency band, and level parameters for each frequency band, a level parameter representing a total power of the two channels for a frequency band;
converting the balance parameters and the level parameters into power values of the first channel for each frequency band and power values of the second channel for each frequency band;
producing a lowband output signal the lowband output signal having a lowband stereo signal, wherein the producing comprises receiving the encoded stereo signal having two channels included in the bit stream;
generating a synthetic highband signal using the lowband output signal;
adjusting the synthetic highband signal according to the power values of the first channel for each frequency band and the power values of the second channel for each frequency band to obtain an adjusted highband signal; and
combining the adjusted highband signal and the lowband output signal.