Stereo Image Widening via Sum-Difference HRTF Processing
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Solution Overview
Problem
Conventional audio playback systems often limit the stereo image to the space between closely spaced speakers, which can result in an undesirable narrow listening experience, and widening this image is challenging due to practical limitations in speaker placement.
Innovation Solution
The technique involves converting a stereo audio signal into a sum-difference signal, applying head-related transfer function (HRTF) processing and distortion to the difference channel, and upsampling and downsampling to produce an output stereo audio signal, which can be implemented using digital audio processing devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If speakers are placed further apart to obtain a wider stereo image, then the stereo image width is improved, but the practical feasibility deteriorates due to limited space for speaker placement
Solution Approach 1:
The patent replaces the mechanical approach of physically spacing speakers apart with a digital signal processing approach. By converting stereo audio to sum-difference signals and applying HRTF processing to the difference channel, the system achieves stereo image widening through acoustic simulation rather than physical separation, thereby resolving the contradiction between desired image width and practical placement constraints
Solution Approach 2:
The patent changes the parameters of the audio signal itself rather than the physical parameters of the speaker system. By manipulating the sum-difference signal components and applying frequency-dependent filtering through HRTF, the system alters the perceived acoustic characteristics to create a wider stereo image without changing the physical speaker configuration
2Area of stationary object
If HRTF processing is applied to both sum and difference channels, then the stereo image widening effect is improved, but the processing complexity increases
Solution Approach 1:
The patent applies different processing strategies to different signal components based on their specific characteristics. The difference channel, which contains the stereo separation information, receives full HRTF processing to achieve widening, while the sum channel (containing mono information) receives simplified or no HRTF processing, optimizing the balance between effect quality and processing complexity
Data Source
AI summary
A stereo image can be widened by converting a stereo audio signal into a sum-difference audio signal, applying HRTF processing to the difference channel, and producing an output stereo audio signal. A stereo image can also be widened by receiving a stereo signal, converting the stereo signal into a sum-difference signal, applying HRTF processing to only the difference channel, upsampling the sum-difference signal, applying distortion, downsampling the sum-difference signal, and converting the sum-difference signal into a stereo signal. A system for widening a stereo image can comprise an input module configured to convert a stereo audio signal into a sum-difference audio signal, an HRTF module configured to apply HRTF processing to only the difference channel, a distortion module configured to apply a first distortion to the sum channel and a second different distortion to the difference channel, and an output module configured to produce an output stereo audio signal.