Multichannel Audio Coding with Time-Delay Spatial Reconstruction
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Solution Overview
Problem
Current multi-channel audio coding systems face bandwidth limitations due to the need for separate encoding of multiple channels, resulting in less than optimal audio quality and inability to produce the depth of audio that multi-channel systems can achieve, especially in wireless communication systems where bandwidth is a constraint.
Innovation Solution
An apparatus and method that determine time delays between audio signals to generate a third signal, which is combined with the first signal to produce a fourth signal, allowing for better channel separation without separate channel encoding, and uses techniques like MPEG-2 AAC or MPEG-1 Layer III for encoding, dividing signals into frequency bands or time frames to account for time and energy differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multi-channel audio signals are encoded separately, then audio quality and channel separation are improved, but bandwidth requirements increase significantly
Solution Approach 1:
The patent combines multiple audio channels into a single down-mixed channel for transmission, reducing bandwidth requirements. The encoder mixes multiple input channels (e.g., 5.1 surround channels) into one mono or stereo down-mixed signal that can be transmitted over bandwidth-constrained wireless connections while preserving spatial audio information through parametric data.
Solution Approach 2:
The patent transforms the audio signal from time-domain waveforms to frequency-domain parameters using Fourier transforms and spectral analysis. By representing audio in terms of frequency bins, amplitudes, and phases rather than raw samples, the system achieves efficient compression and transmission of multi-channel audio over limited bandwidth while maintaining perceptual quality.
2Quantity of substance
If down-mixed signals are used to reduce bandwidth, then bandwidth requirements are reduced, but time and level differences between channels are lost
Solution Approach 1:
The patent introduces parametric data as an intermediary that carries spatial information between the down-mixed audio signal and the reconstructed multi-channel output. The parametric data includes inter-channel time differences (ICTD), inter-channel level differences (ICLD), and spectral information that mediate the reconstruction of spatial audio characteristics at the decoder without requiring separate channel transmissions.
Solution Approach 2:
The encoder performs preliminary analysis of the multi-channel audio signal to extract and encode spatial parameters (time delays, level differences, spectral information) before down-mixing. This preliminary extraction of spatial cues ensures that the information needed for accurate spatial reconstruction is preserved in the parametric data, even though the full multi-channel signal is compressed into a single down-mixed stream.
3Quantity of substance
If conventional down-mixing is applied, then bandwidth is reduced, but audio depth and spatial perception are degraded
Solution Approach 1:
The patent adds a parametric dimension to the traditional audio signal representation. Instead of only transmitting time-domain or frequency-domain audio samples, the system incorporates a separate parametric data dimension that carries spatial and spectral information. This additional dimension enables the decoder to reconstruct multi-channel spatial audio with proper depth and positioning from a single down-mixed channel transmission.
Solution Approach 2:
The patent embeds parametric spatial information within the down-mixed audio bitstream in a nested structure. The parametric data is integrated into the audio codec framework (such as AAC or MP3), where it coexists with the compressed audio samples. This nesting allows the decoder to access both the down-mixed audio signal and the spatial parameters simultaneously, enabling accurate spatial reconstruction without increasing transmission bandwidth.
Data Source
AI summary
An apparatus configured to: determine at least one time delay between a first signal and a second signal; generate a third signal from the second signal dependent on the at least one time delay; and combine the first and third signal to generate a fourth signal; divide the first and second signals into a plurality of time frames; determine for each time frame a first delay associated with a start of the time frame of the first signal and a second time delay associated with an end of the time frame of the first signal; select from the second signal at least one sample in a block defined as starting at the combination of the start of the time frame and the first time delay and finishing at the combination of the end of the time frame and the second time delay; and stretch the selected at least one sample to equal the number of samples of the first frame.