Colorless Elevation Cue Generation with All-Pass Filter Networks
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Solution Overview
Problem
Existing audio processing technologies struggle to effectively encode spatial cues into monaural audio signals, limiting the ability to create immersive and differentiated audio experiences, particularly in mono-to-stereo upmixing scenarios.
Innovation Solution
The use of allpass filters and Hilbert Transforms to process monaural signals, generating multiple channels with spatial cues by determining target amplitude responses and applying frequency-dependent phase shifts, allowing for perceptual soundstage modification (PSM) to enhance spatial perception.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional audio processing methods are used to encode spatial cues into monaural signals, then the implementation is simple, but the spatial perception and immersive audio experience are limited
Solution Approach 1:
The patent applies frequency-dependent phase shifts to encode spatial cues, transforming the monaural signal parameters to create perceptual soundstage modification. This changes the temporal characteristics of the audio signal to convey spatial information without requiring multiple physical channels.
Solution Approach 2:
The allpass filter acts as an intermediary that processes the monaural signal to embed spatial cues. The filter modifies the phase relationships of different frequency components, creating an intermediate representation that contains both the original audio and encoded spatial information.
2Measurement precision
If multiple speakers and amplifiers are used to create immersive audio experiences, then the spatial perception is enhanced, but the hardware complexity and cost increase
Solution Approach 1:
The patent encodes spatial information in the temporal dimension through phase shifts rather than requiring additional spatial dimensions (multiple speakers). By manipulating the phase relationships of frequency components over time, the system creates virtual spatial cues from a single monaural input.
Solution Approach 2:
The allpass filter creates a processed version of the original monaural signal that contains encoded spatial cues. This copied and transformed signal provides the spatial perception effect without requiring physical duplication of audio channels through multiple speakers.
3Measurement precision
If frequency-dependent phase shifts are applied to encode spatial cues, then the spatial perception is improved, but the signal processing complexity increases
Solution Approach 1:
The system applies controlled phase shifts to different frequency components of the monaural signal. By modifying the phase parameter of frequency components in a frequency-dependent manner, the patent encodes spatial cues that affect perceived soundstage position and elevation.
Solution Approach 2:
The audio signal is processed in terms of its frequency components, with different phase shifts applied to different frequency bands. This segmentation in the frequency domain allows for precise control of spatial cues while using standard audio processing techniques.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances spatial perception by creating immersive audio experiences, differentiating sound sources, and reducing the number of required speakers and amplifiers, while maintaining a clear and clarified target audio portion within the mix.
Implementation Method 1
determine a target amplitude response for mid- or side-components of the plurality of resulting channels, based upon a spatial cue associated with a frequency-dependent phase shift
Implementation Method 2
apply a first Hilbert Transform to the high frequency component to generate a first left leg component and a first right leg component, the first left leg component being 90 degrees out of phase with respect to the first right leg component
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.