Bark-Scale Phase Locking for Audio Time Scale Modification
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Solution Overview
Problem
Frequency-domain time scale modification algorithms introduce artifacts like reverberation and loss of sound presence due to phase incoherence, resulting in lower quality sound, especially for polyphonic sounds, which are not effectively addressed by existing phase locking techniques.
Innovation Solution
The use of spectral bands based on the Bark scale for phase locking, where phases are rotated only for a limited number of spectral lines near the peaks, and the remaining lines are handled using the phase vocoder algorithm, distributing computational resources more effectively and maintaining phase coherence in critical bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If frequency-domain time scale modification is used to achieve higher quality for polyphonic sounds, then sound quality is improved, but computational cost increases
Solution Approach 1:
The spectrum is divided into multiple bands, with different phase processing strategies applied to different bands. Critical bands undergo phase locking while non-critical bands use standard phase vocoder processing, segmenting the computational workload based on perceptual importance.
Solution Approach 2:
Phase locking is applied selectively only to spectral lines within critical bands rather than uniformly across the entire spectrum. This localizes the computationally intensive phase locking operation to regions where it provides the most perceptual benefit.
2Object-generated harmful factors
If rigid phase locking is applied to eliminate reverberation artifacts, then reverberation is reduced, but artificial or synthetic sound quality increases
Solution Approach 1:
Phase locking is applied locally only within critical bands rather than globally across the entire spectrum. This localized approach eliminates reverberation artifacts in perceptually critical regions while preserving natural sound characteristics in non-critical regions.
Solution Approach 2:
Instead of applying phase locking to all spectral lines (excessive action), the invention applies it only to spectral lines within critical bands (partial action). This partial application is sufficient to eliminate perceptible artifacts while avoiding the artificial effects of over-processing.
3Object-generated harmful factors
If scaled phase locking is used to control artificiality through scaling factor, then artificial effects are reduced, but overall sound quality remains low
Solution Approach 1:
The invention applies different processing strategies to different spectral regions: phase locking within critical bands and standard phase vocoder processing outside critical bands. This local differentiation eliminates the need for scaling factors while achieving both artifact reduction and high sound quality.
Data Source
AI summary
This invention improves the perceived quality of frequency-domain time scale modification by selection of spectral bands used in phase locking based upon a Bark scale according to the variation in human hearing frequency response. A spectral peak is identified for each band. At these peaks the phases are rotated using the phase vocoder algorithm. For a few spectral lines near these peaks, the phase differences are copied from the non-rotated spectrum. The number selected is preferably 4. Remaining spectral lines within each spectral band located farther from the peak are phase rotated using the phase vocoder algorithm. The boundaries of the spectral bands may be adjusted based upon the digital audio data to maintain important frequency groups within the same spectral band.