Multi-Band Compressor Threshold Coupling for Timbre Preservation

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Solution Overview

Problem

Multi-band compression techniques often distort audio playback by altering the timbre, making the sound unnatural, as they apply different gain values to each frequency band independently without considering the overall audio signal level, leading to frequency-dependent distortion.

Innovation Solution

The implementation of time-varying thresholds in each frequency band, which are adaptive based on the audio signal level in other bands, ensures that if one band approaches its distortion threshold, others also receive gain reduction, thereby maintaining a natural sound quality.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If multi-band compression applies different gain values to each frequency band independently, then distortion threshold is controlled for each band, but timbre is drastically altered and sound becomes unnatural

Engineering Contradiction:

Improvedistortion threshold controlVSAvoidtimbre preservation

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The audio signal is divided into multiple frequency bands using a filter bank, allowing independent processing of each band while maintaining overall coherence through the segmentation approach

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements dynamic threshold adjustment where the threshold for each frequency band is no longer fixed but varies over time based on the signal levels in other bands. This dynamic adaptation allows the compressor to respond to changing audio conditions while preserving timbre characteristics

Inventive Principle:

Principle #15Dynamics

2Power

If compression increases playback level to maximize output, then audio playback capability is improved, but frequency-dependent distortion increases

Engineering Contradiction:

Improveplayback levelVSAvoidfrequency-dependent distortion

Core Design Contradiction:

PowerVSObject-affected harmful factors

Solution Approach 1:

The patent changes the parameter of compression threshold from fixed to time-varying, allowing the system to adapt to different playback levels and signal conditions. This enables maximizing playback level while dynamically adjusting compression to prevent frequency-dependent distortion

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS10680569B2Techniques for distortion reducing multi-band compressor with timbre preservation

Publication Date: 2020.06.09 DOLBY LABORATORIES LICENSING CORP

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.