State Variable Equalizer Filter With Fine Corner Frequency Control

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Solution Overview

Problem

Existing digital equalizers in sound recording environments lack the fine-tuning capabilities offered by analog counterparts, particularly in terms of higher resolution control of parameters like corner frequency and Q-factor, which is essential for precise audio signal modification.

Innovation Solution

A state variable filter with two integrating MDACs, where a digital attenuation controller adjusts the attenuation levels of the MDACs in discrete steps to increment or decrement the corner frequency, allowing for more precise control by independently managing the attenuation of each MDAC based on their current levels.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If traditional digital equalizers are used, then the system is simpler and easier to control digitally, but the resolution and precision of parameter control (corner frequency, Q-factor) is insufficient compared to analog counterparts

Engineering Contradiction:

Improveparameter control resolutionVSAvoidequalizer circuit complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The equalizer is divided into multiple independent filter sections (low-pass, high-pass, band-pass, notch filters), each with its own state-variable filter circuit. This segmentation allows precise digital control of individual parameters while maintaining overall system manageability and achieving high resolution control through coordinated operation of discrete filter blocks

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Analog multiplier circuits are introduced as intermediary components between digital control signals and the filter circuits. These multipliers convert digital attenuation values into precise analog control signals that adjust the corner frequency and Q-factor with high resolution, bridging the gap between digital control simplicity and analog precision

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If analog equalizers are used, then fine-tuning capability and parameter resolution are superior, but the system generates more noise and requires higher power consumption

Engineering Contradiction:

Improvefine-tuning capabilityVSAvoidnoise and power consumption

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

Traditional analog control mechanisms (potentiometers, variable resistors) are replaced with digitally-controlled analog multiplier circuits. This substitution eliminates mechanical noise and contact wear while maintaining the fine-tuning capability of analog systems, achieving precise parameter control with lower noise floors and reduced power consumption through efficient digital-to-analog conversion

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS9154100B2Equalizer

Publication Date: 2015.10.06 SOLID STATE LOGIC UK LTD

AI summary

An equalizer (402) is shown, having a state variable filter in which a first MDAC (502) is coupled to a first integrator (503) and a second MDAC (504) is coupled to a second integrator (505) to allow control of the corner frequency of the state variable filter. The MDACs are each configured to provide variable attenuation in a plurality of discrete steps. A digital attenuation controller is coupled to and adjusts the attenuation of the MDACs independently, and effects a one-step increase in the corner frequency of the state variable filter by first determining the attenuation levels of the MDACs, and then controlling the attenuation levels of the MDACs in accordance with their existing attenuation levels.