Multi-channel Audio Encoder Using Parametric Down-mixing
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Solution Overview
Problem
Current multi-channel encoders generate output encoded data at a bit rate that scales linearly with the number of audio channels, making it inefficient to include additional channels without sacrificing playing duration or audio quality.
Innovation Solution
A multi-channel encoder that down-mixes input signals into fewer output channels and generates parametric data to regenerate the original channels, allowing for efficient encoding compatible with two-channel stereo playback while maintaining backwards compatibility with 2, 3, and 4-channel systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multi-channel encoders encode each channel separately at full bit rate, then audio quality is maintained, but the total bit rate scales linearly with the number of channels, reducing playing duration for a given storage capacity
Solution Approach 1:
The encoder merges multiple audio channels into a reduced set of output channels by combining redundant information. Multiple input channels are processed together to generate fewer output channels, while parametric data captures the relationships between original channels, achieving compression without linearly increasing bit rate with channel count
Solution Approach 2:
The encoder transforms the representation of audio signals from time-domain waveforms to frequency-domain parameters. By encoding spectral parameters and spatial relationships rather than raw channel data, the system achieves efficient compression that maintains audio quality while reducing the bit rate required per channel
2Adaptability or versatility
If additional audio channels are included in the encoded data, then spatial audio quality and immersion are improved, but the bit rate increases proportionally, requiring sacrifice of playing duration or quality
Solution Approach 1:
The encoder adds a parametric dimension to the audio representation by extracting and encoding spatial parameters, correlation coefficients, and spectral relationships. This additional dimension allows the system to represent multiple channels efficiently through compact parametric data rather than requiring proportional increases in raw channel data
Solution Approach 2:
The encoder extracts essential spatial and spectral characteristics from multiple input channels, separating the core audio information from redundant channel-specific data. By taking out only the necessary parametric information needed to reconstruct or simulate additional channels, the system achieves high spatial audio quality without linear bit rate increases
3Adaptability or versatility
If the encoder generates output compatible with two-channel stereo decoders, then backwards compatibility is achieved, but the ability to fully utilize multi-channel information is limited
Solution Approach 1:
The encoder creates a universal output format that serves multiple functions: it provides standard stereo compatibility for legacy decoders while simultaneously embedding parametric data that enables multi-channel reconstruction for advanced decoders. The same encoded bitstream can be decoded by two-channel stereo systems or multi-channel systems with parametric decoding capabilities
Solution Approach 2:
The encoder performs preliminary processing to separate essential stereo information from additional spatial parameters during encoding. This preliminary action ensures that the core audio content is optimally encoded for stereo playback while spatial enhancement data is prepared for potential reconstruction, allowing backwards compatibility without permanent information loss
Data Source
AI summary
There is described a multi-channel encoder (10; 600) for processing input signals conveyed in N input channels to generate corresponding output signals conveyed in M output channels together with complementary parametric data; M and N are integers wherein N>M. The encoder (10; 600) includes a down-mixer for down-mixing the input signals to generate the corresponding output signals, the encoder also comprising an analyser for processing the input signals to generate the parameter data, said parametric data describing mutual differences between the N channels of input signal to allow for regenerating during decoding one or more of the N channels of input signals from the M channels of output signal. Such an encoder (10; 600) is capable of providing highly efficient data encoding and also of being backwards compatibility with relatively simpler decoders having fewer than N decoding output channels. The invention also concerns decoders (800) compatible with such a multi-channel encoder (10; 600).