Adaptive Filter for Musical Instrument Resonance Measurement
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Solution Overview
Problem
Existing methods for amplifying acoustic musical instrument sounds often result in howling and fail to accurately reproduce resonant sounds, as they rely on piezoelectric pickups or FIR filters that require unreliable impulse response measurements.
Innovation Solution
A coefficient measurement apparatus with an adaptive filter that estimates and updates a transfer function to process pickup signals, allowing for reliable reproduction of resonant and reverberant sounds without measuring impulse responses, thereby reducing the risk of howling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a piezoelectric pickup is used to pick up string vibrations, then the risk of howling is reduced, but the resonant sound of the acoustic musical instrument cannot be sufficiently picked up
Solution Approach 1:
The invention combines the outputs of both the piezoelectric pickup (which captures string vibrations with low howling risk) and the microphone (which captures resonant sounds effectively) through signal processing. The pickup signal and microphone signal are processed together to produce an output that includes both the direct string vibration and the resonant body sound, resolving the contradiction between avoiding howling and capturing resonance.
Solution Approach 2:
The invention introduces an intermediary signal processing system that includes delay elements and mixing circuits. This intermediary system processes the pickup signal by adding delayed versions of the signal to simulate acoustic resonance, thereby compensating for the pickup's inability to directly capture body resonance while maintaining the low howling characteristics of the piezoelectric pickup.
2Measurement precision
If acoustic effects such as delay or reverb are imparted to reproduce resonance sound, then the resonant sound can be reproduced, but a resonance feeling such as box resonance cannot be reproduced
Solution Approach 1:
The invention changes the parameters of the signal processing by using multiple different delay times corresponding to different resonance frequencies of the instrument body. Instead of using a single reverb effect, the system applies multiple delayed signals with specific delay periods that match the physical resonance characteristics of the instrument, thereby accurately reproducing box resonance feelings.
Solution Approach 2:
The invention segments the resonance reproduction into multiple discrete delay components rather than using a single integrated reverb effect. Each delay element corresponds to a specific resonance mode of the instrument body, allowing independent control and adjustment of different resonance frequencies to accurately reproduce the complex resonance characteristics.
3Measurement precision
If an FIR filter is used to perform signal processing to reproduce echo feeling, then the echo feeling can be reproduced, but measurement variation is high and reliable measurement cannot be achieved
Solution Approach 1:
The invention performs preliminary determination of the delay period based on the physical specifications of the musical instrument (such as body dimensions and resonance characteristics) before actual signal processing. This preliminary action establishes fixed delay times that correspond to the instrument's natural resonance frequencies, eliminating the need for repeated impulse response measurements and achieving consistent, reliable results.
Solution Approach 2:
Instead of repeatedly measuring impulse responses which cause high measurement variation, the invention creates a copied model of the resonance characteristics based on the instrument's physical specifications. This copied model is then used for signal processing, eliminating measurement variability while preserving the essential echo and resonance feelings.
4Measurement precision
If the vibrator is used to measure impulse response, then the impulse response can be measured, but the measured resonance characteristics are different from those of actual play since the vibrator is brought into contact with the musical instrument
Solution Approach 1:
The invention introduces a microphone as an intermediary measurement device that captures the actual sound radiated by the instrument during normal play. Instead of directly contacting the instrument with a vibrator, the microphone non-invasively records the resonance characteristics as they naturally occur during actual playing, thereby achieving accurate measurement that reflects real performance conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables full and reliable reproduction of acoustic musical instrument resonance, including body resonance, without noise or feedback loops, ensuring accurate sound reproduction and minimizing measurement variability.
Implementation Method 1
an adaptive filter that processes the pickup signal... The adaptive filter estimates a transfer function associated to resonance of the musical instrument and a transfer function of an acoustic space formed from the musical instrument to the microphone. The adaptive filter generates an output signal by processing the pickup signal using the estimated transfer function. The adaptive filter also updates the transfer function using a difference between the output signal and the microphone signal
Implementation Method 2
a microphone input terminal that receives a microphone signal acquired by a microphone
Data Source
AI summary
In a coefficient measurement apparatus, a line input terminal receives a pickup signal that is generated based on a string vibration of a musical instrument. A microphone input terminal receives a microphone signal acquired by a microphone that collects sounds of the musical instrument. An adaptive filter estimates a transfer function associated to resonance of the musical instrument and a transfer function of an acoustic space formed from the musical instrument to the microphone, generates an output signal by processing the pickup signal using the estimated transfer function, and updates the transfer function using a difference between the output signal and the microphone signal as a reference signal.