RIFF: Robust IIR Fitting & Filtering

• Generate robust IIR Zero-Pole-Gain filter models to match the measured transfer functions.

• What's New!

  - Added support for AAA Algorithm for Rational Approximation
  - Simplied SysID via guided workflow.
  - Improved fitting algorithm 
  - Option to generate MINIMUM_PHASE models without any right-half plane zeros.
  - Option to account for input-output delays 
  - One click install
  

• Compatibility

        -   MATLAB R2023b+ (check older releases for older MATLAB R2022a+ versions)
  

• Toolboxes Required

        -   Control System Toolbox
        -   System Identification Toolbox
        -   Global Optimization Toolbox
        -   Curve Fitting
        -   RF Toolbox   (else unselect rationalfit & AAA)
  

• Other Features

  - Uses the chosen optimizer to find the best parameters (see below) that maximizes the goodness of fit.
                    - filter order
                    - fitting algorithm
                    - weighting filter 
                    - Frequency limits
                    
  - System identification is done using 
                    - Subspace identification (N4SID)
                    - Vector fitting 
                    - Complex-curve fitting algorithms
                    - Adaptive Antoulas–Anderson (AAA) Algorithm (Y. Nakatsukasa, O. Sète, and L. N. Trefethen)
  

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  - Calculates the associated uncertainties & the full covariance matrix.
  
  
  - Options to estimate the noise floor & dampen sharp resonances via smoothing the complex transfer function.
  

• To Install

        - Click & install using the mlappinstall file 
  

• To Launch App

        - Launch from the Apps toolbar
        - Or type RIFF from the command line
  

• Input data format

  - Text-files (.txt,.csv) 
              - Valid formats: {f a b}, {w a b}, {f a ib}, {w a ib}, {f a+ib}, {w a+ib}
              
  - Workspace Variables 
              - {Frequency,Complex TransferFunction}
              - {Frequency Response Data (FRD) Model}
              
  - HP-Agilent-Keysight Spectrum Analyzer measurements
             - {SDF .DAT files}
             
  - Input & Output time series and their sampling frequencies
  
  - LISA Technology Package Data Analysis (LTPDA) Analysis Object (AO)
  

• Output

     - FIT_RESULT Structure containing 
               - Identified ZPK with the associated uncertainties  (FIT_RESULT.ZPK)
               - Goodness of fit (FIT_RESULT.gof)
               - Full covariance matrix. (FIT_RESULT.ZPK.parameterCovarianceMatrix)
               - Results from the intermediate stages (FIT_RESULT.intermediate)
               - FRD model & filtered transfer functions
               - Optimization details (FIT_RESULT.options.Optimization)
               - LIGO FOTON Compatible Second-Order-Section filters (when saved to file)                   
  

• For command-line use (+finer control)

        - use fitTF.m
  

• Developed to aid

  - Design of control & calibration filters at gravitational wave (GW) observatories.
  
  - Design of feedforward & feedback filters for platform stabilization & seismic noise isolation.
  
  - Time domain subtraction of the noise sources that linearly/bi-linearly couple to the GW strain data.
  

• Related Publication
   
    Bilinear noise subtraction at the GEO 600 observatory
    N. Mukund et al.   Phys. Rev. D 101 102006, May 2020

• License

  RIFF is released under the terms of the GNU General Public License v3.0.

How to use RIFF WorkFlow

Fit a text-file measurement

Improve Fit using Bayesian Adaptive Direct Search

Account for possible Input-Output Delay

Fit Multiple HP/Agilent/Keysight Spectrum Analyzer Measurements (SDF .DAT Format)

Use a Minimim Phase Design

Implement Higher Order Fitting for systems with complex TFs

Fit workspace variables

Note: tutorial was made using an older app version

Filter TimeSeries using the modeled the transfer function

Note: tutorial was made using an older app version

• Acknowledgements

  Evgeny Pr (2021). INI Config, MATLAB Central File Exchange. Retrieved February 12, 2021.

  Acerbi, L. & Ma, W. J. (2017). Practical Bayesian Optimization for Model Fitting with Bayesian Adaptive Direct Search In Advances in Neural Information Processing Systems 30, pages 1834-1844. arXiv preprint

  Martin Hewitson et al. LTPDA Toolbox V3.0.13

  Justin Dinale (2021). SDF Importer, MATLAB Central File Exchange. Retrieved February 12, 2021.

• Notes

  To use the Bayesian Adaptive Direct Search (BADS) optimizer, install it from BADS-GitHub and add the folder to MATLAB search path. The app will automatically try to install it from the web, if it's not available.

• Alternatives

  Vectfit MATLAB

  Vectfit Python

  FDIDENT MATLAB

  IIRrational Python