Bass Enhancement Limiter Using Dry-Wet Envelope Mixing

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Solution Overview

Problem

Conventional methods for maintaining audio playback devices within operational limits can result in a choppy listening experience, particularly with bass-heavy content, as they dynamically adjust filter characteristics to prevent distortion, leading to inconsistent loudness and unnatural bass cuts.

Innovation Solution

A dynamic sidechain filter (DSF) system that compares the envelopes of dry and wet audio signals to operational thresholds, calculating gains to mix them proportionally and prevent exceeding operational limits, thereby reducing choppiness and maintaining audio quality.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional methods dynamically adjust filter characteristics to prevent distortion, then operational limits are maintained, but listening experience becomes choppy and bass response becomes unnatural

Engineering Contradiction:
Improveoperational limit maintenanceVSAvoidlistening experience smoothness
Core Design Contradiction:
ReliabilityVSEase of operation

Solution Approach 1:

The system pre-calculates and stores gain values in lookup tables for different signal levels and frequency ranges before actual playback. When processing audio, it simply retrieves pre-computed gain values based on current signal conditions, avoiding real-time dynamic adjustments that cause choppiness while still maintaining operational limits

Inventive Principle:
Principle #10Preliminary action

Solution Approach 2:

The patent replaces continuous dynamic filter characteristic adjustments with a discrete gain application system using lookup tables. Instead of mechanically adjusting filter parameters in real-time, the system substitutes this with retrieving and applying pre-computed gain values, eliminating the choppiness caused by continuous adjustments

Inventive Principle:
Principle #28Mechanics substitution (Replace mechanical system)

2Adaptability or versatility

If bass boosting is applied to enhance low frequency response, then bass enhancement is achieved, but operational limits are exceeded causing distortion and device stress

Engineering Contradiction:
Improvebass enhancement capabilityVSAvoiddistortion prevention
Core Design Contradiction:
Adaptability or versatilityVSReliability

Solution Approach 1:

The system applies different gain values to different frequency ranges and signal levels. By dividing the frequency spectrum into bands and applying localized gain adjustments based on pre-computed lookup tables, it enhances bass in specific frequency ranges without uniformly boosting all frequencies, thus preventing operational limit exceedance and distortion

Inventive Principle:
Principle #3Local quality

Solution Approach 2:

The patent changes the gain parameter dynamically based on signal level and frequency range by retrieving appropriate values from lookup tables. This allows bass enhancement through selective gain application while maintaining operational limits, as the gain values are pre-calculated to prevent distortion at different operating conditions

Inventive Principle:
Principle #35Parameter changes

Data Source

PatentEP3607658B1Limiter for bass enhancement
Publication Date: 2021.12.08 SONOS INC
  • EP3607658B1 patent drawingFigure 1
  • EP3607658B1 patent drawingFigure 2~3
  • EP3607658B1 patent drawingFigure 4

AI summary

A dry audio signal may be received. An envelope of the dry audio signal may be compared to a threshold of the playback device to determine a dry excess. A filter may be applied to the dry audio signal to generate a wet audio signal. An envelope of the wet audio signal may be compared to the threshold to determine a wet excess. Based on the dry and wet excess, a dry gain may be determined for the dry audio signal and a wet gain may be determined for the wet audio signal. The wet audio signal and the dry audio signals may be mixed in proportion to respective gains. The mixed audio signal may avoid exceeding an operational limit associated with audio playback on the playback device.