Multi-Band Compressor Cross-Band Thresholds for Low-Distortion Audio
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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 multi-band compression methods alter the timbre, making the sound unnatural.
Innovation Solution
A multi-band compressor that determines time-varying thresholds for each frequency band based on a combination of fixed thresholds and audio signal levels from other bands, allowing adaptive gain reduction across bands to prevent distortion while preserving timbre.
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 making sound unnatural
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 when needed while preserving the natural balance of frequencies, thus resolving the contradiction between distortion reduction and timbre preservation
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 adjusted based on the current state of other bands, creating a closed-loop system that maintains natural sound while preventing distortion
2Reliability
If fixed thresholds are used for each frequency band, then distortion is controlled, but relative balance amongst frequencies is altered
Solution Approach 1:
The thresholds transition from static fixed values to dynamic time-varying values that automatically adjust based on the audio signal characteristics. This dynamic behavior allows the system to maintain frequency balance naturally while still controlling distortion through the adaptive threshold mechanism
3Power
If playback level is increased to maximize output, then output capability is improved, but distortion increases
Solution Approach 1:
The compressor applies gain reduction in advance before the signal reaches distortion levels by predicting when distortion might occur based on current signal levels and dynamic thresholds. This preliminary action allows the system to maintain higher overall playback levels while preventing distortion from occurring in the first place
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.