Multi-Band Compression Using Dynamic Thresholds to Preserve Timbre
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Solution Overview
Problem
Existing audio playback devices suffer from distortion, particularly when increasing playback levels, due to limited output capabilities and frequency-dependent resonance, which can alter the timbre of the sound, making it unnatural.
Innovation Solution
A multi-band compressor system that adjusts time-varying thresholds in each frequency band based on the audio signal levels and fixed thresholds, ensuring that if one band approaches its limit, others also receive gain reduction to maintain a natural sound quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multi-band compression is applied to reduce distortion, then distortion is reduced, but timbre is altered
Solution Approach 1:
The patent implements dynamic threshold adjustment where the threshold for each frequency band is not fixed but varies over time based on the signal levels in other frequency bands. This allows the compressor to adapt its behavior continuously, reducing distortion while preserving timbre by maintaining natural signal relationships.
Solution Approach 2:
The system uses feedback by monitoring the signal levels in all frequency bands and using this information to adjust the thresholds dynamically. The threshold for each band is computed as a function of the current signal levels, creating a closed-loop control system that preserves timbre while reducing distortion.
2Device complexity
If fixed thresholds are used in each frequency band, then compression is simple to implement, but gain reduction is applied unevenly across bands
Solution Approach 1:
The patent transitions from static fixed thresholds to dynamic time-varying thresholds that automatically adjust based on signal conditions. This maintains relative simplicity while achieving uniform gain reduction across bands by making the thresholds responsive to actual signal levels in each band.
Solution Approach 2:
The system changes the parameter of the threshold from a fixed constant to a time-varying value that is computed dynamically. This parameter change allows the compressor to maintain simplicity in structure while achieving uniformity in gain reduction behavior across all frequency bands.
Data Source
AI summary
Distortion reducing multi-band 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.