Support non integer sample rate. (#60)

* Support non integer sample rate.

* Update SpectrogramGenerator.cs

---------

Co-authored-by: Aksel Haukanes <aksel.haukanes@wartsila.com>
Co-authored-by: Scott W Harden <swharden@gmail.com>

Author: 3 people

src/Spectrogram/Settings.cs

@@ -6,7 +6,7 @@ namespace Spectrogram
 {
     class Settings
     {
-        public readonly int SampleRate;
+        public readonly double SampleRate;
 
         // vertical information
         public readonly int FftSize;
@@ -29,7 +29,7 @@ class Settings
         public readonly double StepOverlapFrac;
         public readonly double StepOverlapSec;
 
-        public Settings(int sampleRate, int fftSize, int stepSize, double minFreq, double maxFreq, int offsetHz)
+        public Settings(double sampleRate, int fftSize, int stepSize, double minFreq, double maxFreq, int offsetHz)
         {
             static bool IsPowerOfTwo(int x) => ((x & (x - 1)) == 0) && (x > 0);
 
@@ -45,7 +45,7 @@ public Settings(int sampleRate, int fftSize, int stepSize, double minFreq, doubl
             // vertical
             minFreq = Math.Max(minFreq, 0);
             FreqNyquist = sampleRate / 2;
-            HzPerPixel = (double)sampleRate / fftSize;
+            HzPerPixel = sampleRate / fftSize;
             PxPerHz = (double)fftSize / sampleRate;
             FftIndex1 = (minFreq == 0) ? 0 : (int)(minFreq / HzPerPixel);
             FftIndex2 = (maxFreq >= FreqNyquist) ? fftSize / 2 : (int)(maxFreq / HzPerPixel);

src/Spectrogram/SpectrogramGenerator.cs

@@ -56,7 +56,7 @@ public class SpectrogramGenerator
     /// <summary>
     /// Number of samples per second
     /// </summary>
-    public int SampleRate { get => Settings.SampleRate; }
+    public double SampleRate { get => Settings.SampleRate; }
 
     /// <summary>
     /// Number of samples to step forward after each FFT is processed.
@@ -218,7 +218,7 @@ public List<double[]> GetMelFFTs(int melBinCount)
 
         var fftsMel = new List<double[]>();
         foreach (var fft in FFTs)
-            fftsMel.Add(FftSharp.Mel.Scale(fft, SampleRate, melBinCount));
+            fftsMel.Add(FftSharp.Mel.Scale(fft, (int)SampleRate, melBinCount));
 
         return fftsMel;
     }