Dual Peak Detector Circuit for Low-Latency Fundamental Frequency Detection

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Solution Overview

Problem

Existing audio signal processing technologies face challenges in detecting the fundamental frequency of musical signals with minimal latency, especially for bass instruments in the 20-80 Hz range, due to transient response issues and harmonic interference.

Innovation Solution

The use of dual peak detectors operating on the audio signal and its inverse, with a decay time constant proportional to the time period between voltage peaks, to isolate the fundamental frequency and eliminate harmonic components, thereby reducing latency and improving frequency tracking accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If filtering is applied to improve frequency tracking for complex musical signals, then frequency tracking accuracy is improved, but transient response latency increases

Engineering Contradiction:

Improvefrequency tracking accuracyVSAvoidtransient response latency

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent extracts and removes harmonic components from the audio signal by comparing the original signal with a synthesized version containing harmonics. This extraction process eliminates harmful harmonic interference without requiring filtering operations that would introduce transient latency, thereby achieving accurate fundamental frequency detection with minimal delay.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces an intermediary synthesized signal that mirrors the fundamental frequency but excludes harmonics. This intermediary signal serves as a reference to compare against the original audio signal, allowing the system to isolate and detect the fundamental frequency component without the need for filtering, thus avoiding transient response issues.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Speed

If the decay time constant is made very short to reduce latency, then transient response speed is improved, but frequency tracking accuracy deteriorates due to harmonic interference

Engineering Contradiction:

Improvetransient response speedVSAvoidfrequency estimation accuracy

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

The patent converts the harmful effect of harmonics into a beneficial process by using the difference between the original signal (containing harmonics) and the synthesized signal (without harmonics). This difference signal isolates the fundamental frequency component, allowing fast decay time constants to be used without suffering from harmonic interference, thus achieving both speed and accuracy.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent dynamically adjusts the decay time constant parameter based on the detected fundamental frequency. By making the decay time proportional to the fundamental period, the system maintains optimal transient response characteristics across different frequencies while preserving frequency tracking accuracy through the harmonic elimination process.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If a fixed decay time constant is used to simplify the circuit, then device complexity is reduced, but frequency tracking performance deteriorates for bass instruments

Engineering Contradiction:

Improvecircuit complexityVSAvoidfrequency detection accuracy for bass

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent implements a dynamic decay time constant that is proportional to the fundamental period of the detected frequency. This dynamic adjustment allows the circuit to adapt to different frequency ranges, particularly improving performance for bass instruments with long periods, while maintaining reasonable complexity through the proportional relationship rather than requiring complex adaptive algorithms.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS11289062B2Fundamental frequency detection using peak detectors with frequency-controlled decay time

Publication Date: 2022.03.29 SECOND SOUND LLC

AI summary

Methods and digital circuits provide frequency correction to frequency synthesizers. Dual switched-capacitor voltage detectors connected to an input signal periodically sample the voltage of the input signal, and then determine a fundamental frequency of the input signal from the output of the dual switched-capacitor voltage detectors. The sample period of the dual switched-capacitor voltage detectors is proportional to a time period between a previous pair of voltage peaks detected in the input signal, thereby eliminating harmonic components in the original signal which might otherwise cause errors in frequency estimation without causing unwanted sluggishness in the transient response of the frequency detection process. The time period between the previous pair of detected voltage peaks is used to create a decay signal that initiates a capacitor decay time for each voltage detector. Two additional digital methods of extracting the fundamental frequency as well as an envelope of an analog audio signal are also described, one utilizing a sliding sample rate, and the other utilizing a fixed sample rate.