Allpass Filter Networks for Colorless Monaural Spatial Cue Encoding
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Solution Overview
Problem
Existing audio encoding technologies struggle to effectively incorporate spatial cues into monaural audio signals, limiting the ability to create immersive and differentiated audio experiences in conferencing, video playback, and co-watching scenarios.
Innovation Solution
A method and system that utilize allpass filters and Hilbert Transforms to encode spatial cues into monaural signals, generating multiple channels with targeted amplitude responses and phase shifts, allowing for perceptual soundstage modification (PSM) to enhance spatial perception.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional audio encoding methods are used, then the system is simple and easy to implement, but spatial perception and immersion are limited
Solution Approach 1:
The patent replaces physical spatial arrangement mechanisms with signal processing mechanisms. Instead of using multiple physical speakers and amplifiers to create spatial effects, the invention uses allpass filters and Hilbert transforms to encode spatial cues directly into the audio signal, achieving spatial perception through mathematical transformations rather than physical hardware configurations.
Solution Approach 2:
The patent changes the phase parameters of audio signals using allpass filters with frequency-dependent phase shifts. By modifying the phase response while maintaining amplitude characteristics, the system encodes spatial information into the signal itself, enabling spatial perception without changing the physical audio system configuration.
2Reliability
If multiple amplifiers and speakers are used to create spatial audio effects, then spatial perception is improved, but system complexity and cost increase
Solution Approach 1:
The patent creates virtual spatial copies of audio sources through signal processing. Instead of physically duplicating speakers and amplifiers for different spatial positions, the invention generates multiple virtual audio channels with encoded spatial cues that simulate the effect of multiple physical sources, achieving spatial immersion with a single physical speaker system.
Solution Approach 2:
The patent makes a single speaker system perform multiple spatial functions simultaneously. By encoding different spatial cues into different frequency bands and time segments of the audio signal, one physical speaker can create the perception of multiple sound sources at different locations, eliminating the need for multiple dedicated speakers for each spatial position.
3Measurement precision
If spatial cues are encoded into monaural signals, then voice intelligibility is improved, but the encoding process becomes more complex
Solution Approach 1:
The patent segments the audio signal into different frequency bands and applies different allpass filter configurations to each band. By dividing the signal processing into manageable frequency segments, the system can encode spatial cues selectively in frequency regions that enhance voice intelligibility without overly complicating the entire encoding process.
Solution Approach 2:
The patent introduces allpass filters as intermediary elements between the input audio signal and the output encoded signal. These filters serve as mediators that transform the signal in controlled ways to embed spatial information while preserving voice intelligibility, making the encoding process more systematic and manageable.
Data Source
AI summary
A system includes one or more computing devices that encode spatial perceptual cues into a monaural channel to generate a plurality of output channels. A computing device determines a target amplitude response for the mid and side channels of the plurality of output channels, defining a spatial perceptual associated with one or more frequency-dependent phase shifts. The computing device determines a transfer function of a single-input, multi-output allpass filter based on the target amplitude response and determines coefficients of the allpass filter based on the transfer function, and processes the monaural channel with the coefficients of the allpass filter to generate the plurality of channels having the encoded spatial perceptual cues. The allpass filter is configured to be colorless with respect to the individual output channels, allowing for the placement of spatial cues into the audio stream to be decoupled from the overall coloration of the audio.