Filter Device for Electronic Musical Instrument Tone Color
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Solution Overview
Problem
Existing electronic musical instruments struggle to replicate the nuanced tone color changes of acoustic pianos, particularly in controlling the amplitude ratio of harmonic tones, which are fixed and monotonous due to limitations in filter circuit technology.
Innovation Solution
A filter device with a secondary IIR filter structure, utilizing a filter coefficient calculation circuit and interpolation methods to dynamically adjust filter coefficients based on performance parameters like turnover frequency and gain, approximating the ideal filter characteristics of an acoustic piano.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional filter circuit with cutoff frequency fc and Q parameters is used, then the filter characteristics can be adjusted, but the tone color change cannot replicate the acoustic piano's natural harmonic tone attenuation
Solution Approach 1:
The patent transforms the conventional filter parameters (cutoff frequency fc and Q) into new parameters (turnover frequency f0 and gain A) that directly control the filter characteristics to match acoustic piano behavior. The transfer function is redefined as H(z) = (1 - α) / (1 - αz^-1) + α / (1 - βz^-1), where α and β are derived from f0 and A, enabling precise control over harmonic tone attenuation patterns that replicate acoustic piano tone color changes across different performance strengths.
2Quantity of substance
If waveform data is repeated after attack time in PCM method, then memory capacity is reduced, but tone colors become fixed and monotonous
Solution Approach 1:
The patent introduces time-varying filter parameters that dynamically change during sound reproduction. The gain parameter A is made time-dependent to simulate the natural decay of harmonic tones in acoustic pianos, where higher order harmonics attenuate faster over time. This dynamic adjustment of filter coefficients based on elapsed time since attack enables continuous tone color variation without requiring additional waveform data, maintaining memory efficiency while eliminating monotony.
3Manufacturing precision
If the turnover frequency f0 is changed to adjust filter characteristics, then the maximum attenuation level changes, but the turnover frequency itself shifts position
Solution Approach 1:
The patent separates the control of turnover frequency position from the control of attenuation level by using two independent parameters: f0 determines the frequency position where maximum attenuation occurs, while A controls the depth of attenuation. This decoupling allows precise independent adjustment of each characteristic, preventing the unintended shifting of turnover frequency when adjusting attenuation levels, and enabling accurate replication of acoustic piano filter characteristics.
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 effectively replicates the tone color changes of an acoustic piano by dynamically adjusting filter coefficients, allowing for extensive tone color variation and realistic harmonic tone attenuation, enhancing the musical experience.
Implementation Method 1
The filter device includes a secondary IIR filter having a transfer function H(z) = (1-α)/(1-αz^-1) + α/(1-βz^-1), where z is a delay operator, and α and β are filter coefficients satisfying the following relational expression: 0 < α < 1 and 0 < β < 1
Implementation Method 2
Tone color of an acoustic musical instrument is changed according to change of the amplitude ratio of a harmonic tone in relation to a fundamental tone. In particular, when tone color is changed according to strong and weak of performance, as a musical instrument is performed strongly, the amplitude ratio of a high order harmonic tone becomes higher.
Data Source
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AI summary
In a filter device, a filter coefficient calculation circuit (26) has a parameter table. The parameter table stores a plurality of sets of filter coefficients associated with a first parameter based on a frequency and a second parameter based on respective plurality of levels representing a degree of attenuation or enhancement of a gain of a filter in filter characteristics. The filter coefficient calculation circuit (26) extracts a set of filter coefficients from a parameter table (35) with the use of the first parameter and the second parameter determined according to a frequency and a strength of a musical sound signal, and outputs the extracted set of filter coefficients to the filter (22). The filter circuit (22) performs filter processing for the musical sound signal, based on the filter characteristics determined by the set of filter coefficients.