Issue471 check formant gap

[towsey]

Title of PR

Detection of Harmonic Events.

What is the purpose of this PR? Fix error in detection of Harmonic Events.

Fixes #471

Changes

There are three major changes: 1: I detrended the array of dct coefficients before determining the maximum coefficient. 2: I removed coefficients 0 to 3 from contention as maximum coefficients. We expect there to be a minimum of three formants and three or more formants can only be detected by coefficients 4 and above. 3: I fill in gaps of one or two frames in a sequence of harmonics. This is a hack. -> this is the new SmoothingWindow parameter

I also made various other changes to unit tests and refactoring of methods.

Issues

Detection of stacked harmonics still requires careful consideration of the appropriate parameter values.

Visual Changes

There are no visual changes to the spectrograms produced by this recognizer.

Final Checklist

• [Anthony ] Assign reviewers if you have permission
• [ ] Assign labels if you have permission
• [ ] Link issues related to PR
• [ ] Link any PRs or issues blocking this PR from being merged
• [ ] Remove/Reduce warnings from edited files
• [ Yes] Unit tests have been added for changes
• [ ] Ensure CI build is passing

[codecov[bot]]

Codecov Report

Merging #498 (35bbc6c) into master (2099caf) will decrease coverage by 38.01%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #498       +/-   ##
==========================================
- Coverage   38.72%   0.70%   -38.02%     
==========================================
  Files         482     481        -1     
  Lines       67466   48881    -18585     
  Branches     7870    7659      -211     
==========================================
- Hits        26123     344    -25779     
- Misses      41252   48487     +7235     
+ Partials       91      50       -41     

Impacted Files	Coverage Δ
...coustics.Shared/Extensions/EnumerableExtensions.cs	0.00% <0.00%> (-67.91%)	:arrow_down:
.../AnalysisPrograms/Recognizers/GenericRecognizer.cs	0.00% <0.00%> (-78.36%)	:arrow_down:
src/AudioAnalysisTools/CrossCorrelation.cs	0.00% <ø> (-45.55%)	:arrow_down:
src/AudioAnalysisTools/DSP/MFCCStuff.cs	0.00% <0.00%> (-74.00%)	:arrow_down:
...c/AudioAnalysisTools/Events/Types/HarmonicEvent.cs	0.00% <0.00%> (ø)
...AudioAnalysisTools/Harmonics/HarmonicParameters.cs	0.00% <0.00%> (-67.65%)	:arrow_down:
...AudioAnalysisTools/Ocillations/Oscillations2010.cs	0.00% <0.00%> (-14.25%)	:arrow_down:
...AudioAnalysisTools/Ocillations/Oscillations2012.cs	0.00% <ø> (-92.97%)	:arrow_down:
src/TowseyLibrary/ImageTools.cs	0.00% <0.00%> (-38.28%)	:arrow_down:
src/TowseyLibrary/MatrixTools.cs	0.00% <ø> (-40.73%)	:arrow_down:
... and 470 more

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[towsey]

I believe the two failing tests are to do with ProcessRunner.

[towsey]

Concerning your comment - "I don't like that we define a harmonic as 3 or more formants (technically only one other frequency is needed other than the fundamental)". The harmonic detection relies upon a DCT which can give spurious results where there are other components contributing to the spectrum. The justification for requiring a minimum of three formants is that this gives two intervals. It is very difficult for a DCT to determine the presence of harmonics given only one interval. Requiring two intervals narrows down the possibility for a spurious result. You previously had to set a high formant gap because the DCT was picking up background components at the low index end of the DCT coefficient array. I have had this problem before but not had time to fix it. The things I have done in this round of fixes has helped a lot. But harmonic detection remains prone to error in presence of background noise.

[towsey]

I have just committed a few more changes including changes to the md documentation. I think this is it for this issue.??