Digital Amplifier Matching Using Corrective Input and Output Filters
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Solution Overview
Problem
Modern digital modeling of tube guitar amplifiers is imperfect due to variations in component tolerance, aging, parasitic components, and speaker impedance, leading to inaccuracies in frequency response that can be perceived by users as flaws, which are difficult to account for in blind A/B testing.
Innovation Solution
The implementation of corrective filters, specifically using an exponential sine sweep and a matched filter, to adjust the digital amplifier model to match the response of a specific individual real guitar amplifier, thereby correcting frequency response deviations and system gain differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a digital amplifier model is created to represent a real guitar amplifier, then the model can be used for consistent A/B testing and digital processing, but the model cannot account for individual variations in component tolerance, aging, and manufacturing differences
Solution Approach 1:
The system performs preliminary measurements on the actual amplifier using exponential sine sweeps to capture its specific frequency response characteristics before creating the digital model. This preliminary action allows the model to be pre-adjusted to match the individual amplifier's unique characteristics, including component tolerances and aging effects, thereby resolving the contradiction between model consistency and measurement precision.
Solution Approach 2:
The system adjusts the digital amplifier model's frequency response parameters to match the measured characteristics of the specific real amplifier. By changing the model's frequency response parameters based on actual measurements, the system maintains both the consistency needed for A/B testing and the precision required to represent individual amplifier variations.
2Measurement precision
If corrective filters are applied to match the digital model to a specific amplifier sample, then frequency response accuracy improves, but the complexity of the modeling system increases
Solution Approach 1:
The system introduces corrective filters as intermediary elements between the digital amplifier model and the input signal. These filters act as mediators that adjust the model's frequency response to match the specific amplifier characteristics without requiring fundamental changes to the model architecture, thereby improving precision while minimizing added complexity.
Solution Approach 2:
The corrective filters are calculated and applied in advance during the modeling process rather than being adjusted in real-time during use. This preliminary calculation of filter parameters simplifies the overall system complexity while still achieving accurate frequency response matching.
3Measurement precision
If the digital amplifier model is adjusted to match individual amplifier variations, then perceived accuracy by users improves, but the ability to generalize the model across multiple amplifier units decreases
Solution Approach 1:
The system applies local adjustments to the digital amplifier model by introducing corrective filters that modify only specific frequency ranges where individual amplifier variations occur. This allows the model to maintain its generalizability for most applications while achieving local precision for individual amplifier matching where needed.
Data Source
AI summary
In one example, a method to match a digital amplifier model to a real guitar amplifier comprises obtaining an amplifier output filter and an amplifier input filter for the real guitar amplifier, using the amplifier output filter and a model output filter to obtain a corrective output filter, using the amplifier input filter and a model input filter to obtain a corrective input filter, and applying the corrective input filter and the corrective output filter to the digital amplifier model. The amplifier output filter and the amplifier input filter can be obtained using exponential sine sweep (ESS) and a matched filter. Other examples and related methods and apparatuses are also disclosed herein.