Phase-amplitude 3-D stereo encoder and decoder
A two-channel phase-amplitude stereo encoding and decoding scheme enabling flexible and spatially accurate interactive 3-D audio reproduction via standard audio-only two-channel transmission. The encoding scheme allows associating a 2-D or 3-D positional localization to each of a plurality of sound sources by use of frequency independent inter-channel phase and amplitude differences. The decoder is based on frequency-domain spatial analysis of 2-D or 3-D directional cues in a two-channel stereo signal and re-synthesis of these cues using any preferred spatialization technique, thereby allowing faithful reproduction of positional audio cues and reverberation or ambient cues over arbitrary multi-channel loudspeaker reproduction formats or over headphones, while preserving source separation despite the intermediate encoding over only two audio channels.
1. A method for two-channel phase amplitude stereo encoding of at least one audio source signal assigned a localization relative to a listener position, the method comprising:
scaling the at least one audio source signal by panning coefficients derived from the localization to generate a multi-channel signal corresponding to a desired multi-channel format; and
matrix encoding the multi-channel signal to generate a 2-channel encoded signal such that the localization of the at least one audio source signal is represented by inter-channel phase and amplitude differences in the 2-channel encoded signal;
wherein the at least one audio source signal comprises a plurality of audio source signals and wherein the multi-channel signal for each of the plurality of audio source signals are combined prior to matrix encoding.
2. The method as recited in claim 1 wherein matrix encoding comprises scaling the multi-channel signal by frequency-independent encoding coefficients derived from the localization to generate the 2-channel encoded signal such that the localization of the at least one audio source is represented by inter-channel phase and amplitude differences in the 2-channel encoded signal, and wherein the localization includes an azimuth angle and an elevation angle, the method further comprising:
generating a first unlocalized audio signal and a second unlocalized audio signal from an unlocalized audio source signal such that the first and second unlocalized audio signals are substantially uncorrelated.
3. The method as recited in claim 1 wherein panning coefficients are derived from an azimuth angle included in the localization by the use of vector based amplitude panning (VBAP) techniques.
4. The method as recited in claim 1 wherein the scaling accommodates a top channel corresponding to an upper hemisphere located above the listening plane and a bottom channel located below the listening plane.
5. The method as recited in claim 1 wherein the multi-channel signal is a six channel signal and wherein the 2-channel encoded signal is a two channel phase-amplitude stereo encoded signal.
6. The method as recited in claim 1 , wherein the total power of the contribution of the at least one audio source signal in the 2-channel encoded signal is equal to the power of the at least one audio source signal regardless of the assigned localization.
7. A method for two-channel phase amplitude stereo encoding of at least one localized audio source signal assigned a localization relative to a listener position and at least one unlocalized audio source signal, the method comprising:
scaling the at least one localized audio source signal by frequency-independent encoding coefficients derived from the localization to generate a 2-channel encoded signal such that the localization of the at least one localized audio source signal is represented by inter-channel phase and amplitude differences in the 2-channel encoded signal;
generating a first unlocalized audio signal and a second unlocalized audio signal from the at least one unlocalized audio source signal such that the first and second unlocalized audio signals are substantially uncorrelated; and
adding the first and second unlocalized audio signals respectively to first and second encoded channel signals of the 2-channel encoded signal.
8. A method for two-channel phase amplitude stereo encoding of at least one localized audio source signal assigned a localization in three dimensions relative to a listener, the method comprising:
scaling the at least one localized audio source signal by frequency-independent encoding coefficients derived from the localization to generate a 2-channel encoded signal such that the localization of the at least one localized audio source signal is represented by inter-channel phase and amplitude differences in the 2-channel encoded signal, the localization including an up-down dimension, a left-right dimension and a front-back dimension; and
generating a first unlocalized audio signal and a second unlocalized audio signal from an unlocalized audio source signal such that the first and second unlocalized audio signals are substantially uncorrelated;
wherein the scaling accommodates a top channel corresponding to an upper hemisphere located above the listening plane and a bottom channel located below the listening plane.