Multi-Band Compressor Threshold Coupling for Low-Distortion Timbre
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Solution Overview
Problem
Multi-band compression techniques alter the timbre of audio signals, leading to unnatural sound when attempting to reduce distortion in playback devices with limited output capabilities, as they apply differing gain values to each frequency band independently, causing frequency-dependent distortion.
Innovation Solution
The implementation of time-varying thresholds in each frequency band, which are adaptive to the audio signal levels in other bands, ensures that if one band approaches its distortion threshold, corresponding thresholds in other bands are adjusted to prevent excessive gain reduction, thereby maintaining a natural sound quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multi-band compression is applied to reduce distortion in each frequency band independently, then distortion is reduced, but timbre is altered and sound becomes unnatural
Solution Approach 1:
The patent merges the compression control of multiple frequency bands by making thresholds interdependent through a coupling factor. Instead of treating each band independently, the threshold for one band is adjusted based on the signal levels and thresholds of other bands, thereby combining their effects to preserve overall timbre while still reducing distortion.
Solution Approach 2:
The patent implements feedback by continuously monitoring the audio signal levels in each frequency band and using this information to dynamically adjust the thresholds. The coupling mechanism creates a feedback loop where changes in one band's signal level influence the thresholds of other bands, allowing the system to adapt and preserve timbre characteristics.
2Reliability
If fixed thresholds are applied to each frequency band to prevent distortion, then distortion is controlled, but gain reduction becomes excessive when other bands are quiet, altering sound balance
Solution Approach 1:
The patent transforms fixed thresholds into dynamic, time-varying thresholds that adapt to the instantaneous signal conditions. The coupling factor enables thresholds to change dynamically based on the relative levels of different frequency bands, allowing the compressor to behave differently depending on the musical context and preserve natural sound balance.
Solution Approach 2:
The patent changes the parameter of threshold values from static to variable by introducing the coupling mechanism. The thresholds are no longer fixed but are modified in real-time based on the signal levels in other frequency bands, allowing the system to maintain distortion control while adapting to preserve sound balance.
3Manufacturing precision
If independent compression is applied to each frequency band, then distortion threshold is met for each band, but relative balance amongst frequencies is altered
Solution Approach 1:
The patent introduces asymmetry in the compression approach by treating bands differently based on their relative signal levels. The coupling factor creates an asymmetric relationship where bands with higher signal levels have more influence on the thresholds of other bands, allowing the system to maintain frequency balance dynamically rather than applying uniform compression.
Data Source
AI summary
Distortion reducing multi-hand compressor with timbre preservation is provided. Timbre preservation is achieved by determining a time-varying threshold in each of a plurality frequency bands as a function of a respective fixed threshold for the frequency band and, at least in part, an audio signal level and a fixed threshold outside such frequency band. If a particular frequency band receives significant gain reduction due to being above or approaching its fixed threshold, then a time-varying threshold of one or more other frequency bands are also decreased to receive some gain reduction. In a specific embodiment, time-varying thresholds can be computed from an average difference of the audio input signal in each frequency band and its respective fixed threshold.