Audio Gain Smoothing for Limiter Threshold Distortion Control
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Solution Overview
Problem
Existing sound generation systems face issues with harmonic distortion due to simple waveform peak limitation, leading to abnormal sounds when input and output signals exceed device limits.
Innovation Solution
A sound generation control device that includes an excess determination unit, absolute value waveform generation, peak hold waveform generation, gain curve generation, and smoothing processing to limit waveform amplitude while suppressing harmonic distortion by generating sound data based on a smoothen gain curve.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If simple waveform peak limitation is performed to limit the amplitude of sound data, then the input and output signals are kept within device limits, but harmonic distortion occurs due to waveform bending and abnormal sound is generated
Solution Approach 1:
The patent applies preliminary action by detecting excess portions in the input waveform before they cause distortion, and pre-processing them through gain adjustment. The excess determination unit identifies portions exceeding the threshold, and the gain adjustment unit applies attenuation gain in advance to prevent waveform bending and harmonic distortion before they occur during normal playback.
Solution Approach 2:
The patent introduces a gain curve as an intermediary element that smoothly transitions between different gain values. Instead of directly clipping the waveform, the gain curve acts as a mediator that gradually adjusts the amplitude, preventing abrupt waveform bending while still limiting the output to stay within device limits. This intermediary approach maintains waveform integrity while achieving amplitude control.
2Object-generated harmful factors
If the waveform amplitude is limited to prevent harmonic distortion, then abnormal sound is suppressed, but the sound output may become less recognizable or require larger/smaller device components
Solution Approach 1:
The patent applies local quality by adjusting the gain only in specific portions of the waveform where excess amplitude occurs, rather than uniformly limiting the entire signal. The gain adjustment unit selectively applies attenuation gain to excess portions identified by the excess determination unit, preserving the recognizability of the sound while preventing distortion only where necessary. This localized approach maintains overall sound quality and recognizability.
Solution Approach 2:
The patent uses partial action by applying gain adjustment only to the extent necessary to prevent distortion. The gain curve is designed to maintain gain values close to 1.0 for most of the waveform, applying attenuation only when and where the waveform exceeds the threshold. This partial adjustment prevents over-limiting that would degrade sound recognizability while still effectively preventing harmonic distortion.
3Object-generated harmful factors
If a complex smoothing process is applied to the gain curve to suppress harmonic distortion, then abnormal sound is reduced, but the device complexity increases
Solution Approach 1:
The patent segments the waveform processing into distinct functional units: excess determination unit for detecting threshold violations, gain curve generation unit for creating the adjustment profile, gain adjustment unit for applying the adjustment, and smoothing processing unit for refining the transition. This segmentation allows each unit to perform a specific function with simple, well-defined operations, reducing overall processing complexity while achieving effective distortion suppression through coordinated operation of the segments.
Data Source
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AI summary
An absolute value waveform generation unit (S03) generates an absolute value waveform (Wab) obtained by converting a level (Lv) of input waveform (Win) into an absolute value when the input waveform includes an excess portion (EX) within which the absolute value of the level exceeds a limiter threshold (Th). A peak hold waveform generation unit (S04) generates a peak hold waveform (Wp) based on the absolute value waveform. A gain curve generation unit (S05) generates a gain curve (Wgn) that indicates a relationship between a gain (Gn) obtained based on a level of the peak hold waveform and input waveform time (Tm). A smoothing processing unit (S06) generates a smoothen gain curve (Wsgn) based on the gain curve by performing a smoothing processing. A sound data generation unit (S07, S08) generates sound data by multiplying a delayed input waveform (Wind) obtained by shifting the input waveform toward a positive time end (Dtp) by the smoothen gain curve.