Integer Bass Boost Filter for Stable Low-Frequency Audio
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Solution Overview
Problem
Existing audio playback devices face challenges in implementing bass boost due to the lack of floating point math capabilities in microprocessors, leading to instability and frequency deviation issues with traditional filter design techniques, especially at low frequencies.
Innovation Solution
The use of an integer bass boost filter with user-settable parameters, employing a coupled form structure that can switch between standard and modified implementations, and incorporating adaptive output gain processing to prevent clipping, allows for effective bass frequency enhancement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional filter design techniques are used with integer coefficient quantization, then the implementation cost is reduced, but pole location accuracy deteriorates leading to instability and frequency deviation
Solution Approach 1:
The patent changes the parameter representation from standard filter coefficients to pole-zero coordinates. By directly specifying pole locations in the z-plane and using integer approximations of these complex coordinates, the system maintains frequency accuracy while enabling integer arithmetic implementation. The key insight is representing filters by their pole-zero locations rather than traditional difference equation coefficients, allowing direct control over frequency response characteristics despite quantization.
2Measurement precision
If floating point math capabilities are added to microprocessors, then bass boost precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent substitutes floating-point arithmetic with integer arithmetic by transforming the filter design domain. Instead of performing floating-point calculations for filter coefficients, the system uses integer mathematics to compute pole-zero locations and their effects on frequency response. This substitution maintains the precision needed for bass boost control while avoiding the need for floating-point hardware, thereby reducing device complexity and cost.
3Productivity
If poles are placed close to the unit circle for low frequency filtering, then bass boost effectiveness is improved, but integer coefficient quantization causes poles to move outside the unit circle causing instability
Solution Approach 1:
The patent implements a feedback mechanism where pole locations are initially placed close to the unit circle for effective bass boost, then iteratively adjusted based on stability checks. The system computes the effect of quantized integer coefficients on pole locations and refines the pole positions to ensure they remain within the unit circle after quantization, thereby maintaining both effectiveness and stability.
Solution Approach 2:
The patent performs preliminary stability analysis before finalizing filter design. By pre-calculating the impact of integer coefficient quantization on pole locations and adjusting pole positions in advance to compensate for expected quantization errors, the system ensures that the final implemented filter remains stable while maintaining bass boost effectiveness.
Data Source
AI summary
Bass frequencies of audio can be boosted using various techniques and tools. The described techniques and tools can be applied separately or in combination. For example, bass frequencies of audio can be boosted using an integer bass boost filter by receiving user-settable parameters, such as “c” and “s” coefficients, and implementing the integer bass boost filter using a coupled form structure implementation and the user-settable parameters. Bass frequencies of audio can also be boosted using an integer bass boost filter that is configured to use any of plural coupled form structure implementations. Bass frequencies of audio can be also be boosted using a linear combination of an input audio signal and output of a high-pass filter.