Audio Encoding Temporal Filter for Signal Quality
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Solution Overview
Problem
Existing audio compression methods that limit bandwidth to reduce data transfer requirements introduce artefacts that impair signal quality, and existing methods for recreating high frequencies from low frequencies are inefficient and do not provide the best perceived quality.
Innovation Solution
The method involves transmitting a temporal filter alongside the frequency-limited signal, which is applied to both the low-frequency and reconstituted high-frequency parts to reshape the signal and correct compression artefacts, using Fourier transforms to generate filters that restore the original signal's spectral characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If bandwidth is limited to reduce data transfer rate, then data transfer requirements are reduced, but compression artefacts are introduced that impair signal quality
Solution Approach 1:
The audio signal is segmented into low-frequency components (transmitted directly) and high-frequency components (reconstructed through spectral broadening). This segmentation allows the system to transmit only essential low-frequency data while generating high-frequency content through processing, thus reducing data transfer requirements while maintaining signal quality.
Solution Approach 2:
A temporal filter is pre-calculated and transmitted alongside the frequency-limited signal. This filter is applied in advance to the reconstructed high-frequency spectrum to correct compression artefacts and reshape the spectrum, ensuring high perceived quality without requiring transmission of the full original signal.
2Quantity of substance
If high frequencies are recreated from low frequencies through spectral enhancement, then data bandwidth is reduced, but the processing complexity increases
Solution Approach 1:
Instead of transmitting the complete original signal, the system transmits a simplified copy containing only low-frequency information. The high-frequency components are then synthesized by applying a temporal filter to broadened spectral data, creating a representative copy that achieves full frequency content with reduced data bandwidth.
Solution Approach 2:
The system changes the spectral parameters of the signal by broadening the spectrum of the frequency-limited signal and then applying temporal filtering. This parameter transformation allows high-frequency content to be generated from low-frequency input, reducing data requirements while maintaining processing efficiency through simple filter application.
3Manufacturing precision
If spectral enhancement is applied to recreate high frequencies, then perceived quality may be improved, but compression artefacts in the low-frequency part remain
Solution Approach 1:
The temporal filter, when applied to the broadened spectrum, serves dual purposes: it reshapes the high-frequency content and simultaneously corrects compression artefacts in the low-frequency portion. This transforms the harmful effect of compression artefacts into a beneficial correction process, improving overall perceived quality.
Solution Approach 2:
The temporal filter performs multiple functions simultaneously: it reshapes the high-frequency spectrum, corrects compression artefacts in the low-frequency part, and maintains the overall signal quality. This multi-functionality allows a single processing step to address multiple quality issues that would otherwise require separate corrections.
Data Source
AI summary
Audio encoding method and device comprising the transmission, in addition to the data representing a frequency-limited signal, of information relating to a temporal filter that is to be applied to the entire enhanced signal, both in its transmitted low-frequency part and in its reconstituted high-frequency part. The application of this filter for reshaping the reconstituted high-frequency part and the correction of compression artefacts present in the transmitted low-frequency part. In this way, the application of the temporal filter, simple and inexpensive, to all or part of the reconstituted signal, makes it possible to obtain a signal of good perceived quality.