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Inverse Filter

Inverse Filter

Overview

A tool for creating and applying a filter to an audio file that "cancels out" a system's frequency response (such as the idiosyncrasies of speakers or microphones) obtained through measurement.

For example, if you have an audio recording from a speaker with slightly weak high-frequency response, you can calculate and apply the inverse characteristic (boosting the high-frequency) to synthesize audio that is closer to an ideal flat response.

Operations

Load Calibration Data

  • Reload from Memory: Imports the latest calibration data measured by tools like the Network Analyzer and currently held in the application's memory.
  • Load File: Loads a previously saved calibration map in .json format.

Filter Design

Adjust the shape of the correction filter based on the loaded data.

  • Max Gain (Regularization): A limit value to suppress excessive amplification during correction. For example, if set to "10dB," even if the original signal has a 20dB drop, it will only be boosted by up to 10dB. This prevents excessive noise amplification.
  • FIR Taps: The resolution/fineness of the filter. Larger values allow for more precise correction but increase computational load. Usually, around 8192 is recommended.
  • Smoothing: Smooths out peaks and dips in the response characteristics.

Audio Processing

  • Input: Select the audio file (WAV format) you wish to process.
  • Process & Save: Saves a new file with the filter applied.

Settings

  • Normalize Output (RMS): Automatically adjusts the output to match the perceived volume of the original file, preventing overall volume changes caused by correction.

Usage Examples

  • Microphone Correction: If a microphone's frequency response is known, applying the inverse characteristic to a recorded voice can result in sound quality that is more faithful to the original.
  • Simple Room Acoustic Correction: Used in research to bring recording results closer to a flat response when played back in a specific room.