Multi-Band Limiter Overlap Filters to Eliminate Dead Zones
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Solution Overview
Problem
Multi-band limiters suffer from a 'dead zone' issue where signals are not properly attenuated across frequency bands, leading to incomplete gain reduction and potential sound recording failures due to excessive peak levels, especially when filters are set to cross at −6 dB.
Innovation Solution
The implementation of an overlap filter configuration where high-band side cutoff frequencies of one filter element are greater than or equal to the low-band side cutoff frequencies of another, allowing components to overlap and set control gains for each band to ensure appropriate limit processing without dead zones, combined with a cross-over filter for flat frequency characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If filters are set to cross at -6 dB to achieve flat frequency characteristic, then frequency response is improved, but dead zones are created where limiter cannot function properly
Solution Approach 1:
The patent segments the frequency band division and limiter application into two independent stages: first dividing frequencies with cross-over filters at -6 dB for flat response, then separately applying limiters to each band. This segmentation allows each stage to optimize its function without compromising the other.
Solution Approach 2:
The patent introduces an intermediary processing stage where divided frequency bands are individually processed by limiters before being recombined. This intermediary step ensures that limiter processing occurs on the original signal levels rather than on already-attenuated signals at band edges.
2Productivity
If independent multi-band limiting is applied to each frequency band, then gain reduction is achieved in specific bands, but dead zones occur where signals are attenuated below threshold and cannot be limited
Solution Approach 1:
The patent applies preliminary frequency band division before limiter processing, allowing the system to prepare separate gain reduction controls for each band. By establishing the band structure in advance, the system can independently manage gain reduction in each band without interference from adjacent band attenuation.
3Stability of the object's composition
If filter slope is not steep to avoid signal loss, then frequency transition is smoother, but signals of same frequency exist in both adjacent bands causing inconsistent limiter application
Solution Approach 1:
The patent changes the parameter of filter crossing point from -3 dB to -6 dB, which provides a clearer separation between adjacent frequency bands. This parameter change reduces the overlap region where the same frequency signals would exist in multiple bands, thereby improving the consistency of limiter application across bands.
Data Source
AI summary
A multi-band limiter, a sound recording apparatus, and a program are provided having a multi-band limit function with a flat frequency characteristic while removing a dead zone of a multi-band limiter. A cross-over filter unit divides an input sound signal into a low-band component, a middle-band component, and a high-band component so that the adjacent bands cross at −6 dB. An overlap filter unit includes a low-band filter element, a middle-band filter element, and a high-band filter element that respectively divide the input sound signal into a low-band component, a middle-band component, and a high-band component, and applies a limit process to divide the input sound signal in such a manner that the low-band component and the middle-band component overlap each other and the middle-band component and the high-band component overlap each other by setting a high-band side cutoff frequency of the low-band filter element to be greater than or equal to a low-band side cutoff frequency of the middle-band filter element and setting a high-band side cutoff frequency of the middle-band filter element to be greater than or equal to a low-band side cutoff frequency of the high-band filter element, and set a control gain by a CG for each band, and an adder combines the components.