Modal Processor Subband Filtering for Lower-Cost Reverberation
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Solution Overview
Problem
The computational cost of implementing modal reverberators and modal processors is high due to the large number of resonant filters required to accurately model acoustic spaces and vibrating objects, leading to significant MIPS requirements.
Innovation Solution
The implementation of a parallel sum of resonant filters is optimized by processing input signals in frequency subbands with non-overlapping pass bands and transition bands, using downsampling, heterodyning, and adjusting mode frequencies and gains to reduce computational complexity, and incorporating a wideband residual filter to account for energy outside assigned subbands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large number of resonant filters are used to accurately model acoustic spaces, then modeling accuracy is improved, but computational cost increases
Solution Approach 1:
The audio frequency spectrum is divided into multiple subbands, with each subband processed by a separate modal reverberator instance. This segmentation allows each instance to handle fewer modes at lower sampling rates, reducing individual computational costs while collectively maintaining overall accuracy through parallel processing of all frequency regions.
Solution Approach 2:
The patent transitions from time-domain processing to frequency-domain processing by applying FFT-based subband decomposition. This dimensional change allows modes to be selectively activated only in frequency subbands where they are relevant, and enables downsampling in the time domain after frequency separation, thereby reducing the number of MAC operations required per sample.
2Productivity
If the sampling rate is reduced to lower computational cost, then processing speed requirement is improved, but mode frequency representation accuracy deteriorates
Solution Approach 1:
By dividing the audio spectrum into subbands and processing each separately at reduced sampling rates, the patent maintains adequate frequency representation for modes within each subband while reducing overall computational burden. Each subband instance operates at a sampling rate sufficient for its frequency range, preserving mode accuracy locally.
Solution Approach 2:
The patent dynamically adjusts the sampling rate parameter for each modal reverberator instance based on its assigned frequency subband. Higher subbands use higher sampling rates to accurately represent high-frequency modes, while lower subbands use lower sampling rates, optimizing the balance between processing efficiency and frequency representation accuracy across the entire spectrum.
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
This approach significantly reduces the computational cost of implementing modal filter systems by processing signals in fewer subbands, achieving efficient and accurate audio processing with reduced MIPS requirements while maintaining interactive control over acoustic features.
Implementation Method 1
downsampling, heterodyning, and adjusting mode frequencies and gains to reduce computational complexity
Data Source
AI summary
The implementation of modal processors, which involve the parallel combination resonant filters, may be costly for applications such as artificial reverberation that can require thousands of modes. In one embodiment, the input signal is decomposed into a plurality of subbands, the outputs of which are downsampled. In each downsampled band, resonant filters are applied at the downsampled sampling rate, and their output is upsampled and filtered to form the band output. In these and other embodiments, a feature of responses of the mode filters have been optimized to minimize an aspect of a residual error after a point in time.