Switch to windowOverlap instead of fourierOverlap

The wording is more clear and accurate with the new window length variable. This commit also
updates the simulator to better handle the new window length functionality.

SyllableDetector/SyllableDetector.swift

@@ -39,7 +39,7 @@ class SyllableDetector: NSObject, AVCaptureAudioDataOutputSampleBufferDelegate
         self.config = config
 
         // initialize the FFT
-        shortTimeFourierTransform = CircularShortTimeFourierTransform(windowLength: config.windowLength, withOverlap: config.fourierOverlap, fftSizeOf: config.fourierLength)
+        shortTimeFourierTransform = CircularShortTimeFourierTransform(windowLength: config.windowLength, withOverlap: config.windowOverlap, fftSizeOf: config.fourierLength)
         shortTimeFourierTransform.windowType = WindowType.Hamming
 
         // store frequency indices

SyllableDetector/SyllableDetectorConfig.swift

@@ -30,9 +30,9 @@ struct SyllableDetectorConfig
     }
 
     var samplingRate: Double // eqv: samplerate
-    var windowLength: Int
-    var fourierLength: Int // eqv: FFT_SIZE
-    var fourierOverlap: Int // eqv: NOVERLAP = FFT_SIZE - (floor(samplerate * FFT_TIME_SHIFT))
+    let fourierLength: Int // eqv: FFT_SIZE
+    let windowLength: Int
+    var windowOverlap: Int // eqv: NOVERLAP = FFT_SIZE - (floor(samplerate * FFT_TIME_SHIFT))
 
     let freqRange: (Double, Double) // eqv: freq_range
     let timeRange: Int // eqv: time_window_steps = double(floor(time_window / timestep))
@@ -46,28 +46,23 @@ struct SyllableDetectorConfig
     mutating func modifySamplingRate(newSamplingRate: Double) {
         // store old things
         let oldSamplingRate = samplingRate
-        let oldFourierLength = fourierLength
-        let oldFourierOverlap = fourierOverlap
+        let oldWindowOverlap = windowOverlap
 
         if oldSamplingRate == newSamplingRate { return }
 
+        // window offset (difference in time between two consecutive windows)
+        // calculated using old values, but should be constant even after the new values
+        let windowOffset = Double(windowLength - oldWindowOverlap) / oldSamplingRate
 
-        // get new approximate fourier length
-        let newApproximateFourierLength = newSamplingRate * Double(oldFourierLength) / oldSamplingRate
-
-        // convert to closest power of 2
-        let newFourierLength = 1 << Int(round(log2(newApproximateFourierLength)))
-
-        // get new fourier overlap
-        let newFourierOverlap = newFourierLength - Int(round(newSamplingRate * Double(oldFourierLength - oldFourierOverlap) / oldSamplingRate))
+        let newWindowOverlap = windowLength - Int(round(windowOffset * newSamplingRate))
 
         // change the to new things
         samplingRate = newSamplingRate
-        fourierLength = newFourierLength
-        fourierOverlap = newFourierOverlap
+        windowOverlap = newWindowOverlap
 
-        DLog("New fourier length: \(newFourierLength)")
-        DLog("New fourier overlap: \(newFourierOverlap)")
+        DLog("Window offset: \(windowOffset)")
+        DLog("Sanity check: \(Double(windowLength - oldWindowOverlap) / oldSamplingRate)")
+        DLog("Window overlap: OLD \(oldWindowOverlap) NEW \(newWindowOverlap)")
     }
 }
 
@@ -234,7 +229,7 @@ extension SyllableDetectorConfig
         }
 
         // fourier length: int
-        fourierOverlap = try SyllableDetectorConfig.parseInt("fourierOverlap", from: data)
+        windowOverlap = try SyllableDetectorConfig.parseInt("windowOverlap", from: data)
 
         // frequency range: double, double
         let potentialFreqRange = try SyllableDetectorConfig.parseDoubleArray("freqRange", withCount: 2, from: data)

SyllableDetector/ViewControllerSimulator.swift

@@ -242,7 +242,10 @@ class ViewControllerSimulator: NSViewController {
         assert(status == noErr)
 
         // processing
-        var nextCount: Int = sd.config.fourierLength + ((sd.config.fourierLength - sd.config.fourierOverlap) * (sd.config.timeRange - 1)), nextValue: Float = 0.0
+        var nextCount: Int = sd.config.windowLength + ((sd.config.windowLength - sd.config.windowOverlap) * (sd.config.timeRange - 1)), nextValue: Float = 0.0
+        if sd.config.windowOverlap < 0 {
+            nextCount = nextCount - sd.config.windowOverlap // since gap is applied even to the first data set
+        }
         var samplePosition: Int64 = 0
         let gcdGroup = dispatch_group_create()
         let gcdQueue = dispatch_queue_create("Encode", DISPATCH_QUEUE_SERIAL)
@@ -296,7 +299,7 @@ class ViewControllerSimulator: NSViewController {
                     }
 
                     // length
-                    var l = sd.config.fourierLength - sd.config.fourierOverlap
+                    var l = sd.config.windowLength - sd.config.windowOverlap
 
                     for ; 0 < l && i < numSamples; ++i, --l {
                         newSamples[i] = v
@@ -325,6 +328,8 @@ class ViewControllerSimulator: NSViewController {
 
                 // append sample buffer
                 if !avWriterInput.appendSampleBuffer(newSampleBuffer!) {
+                    DLog("failed to write sample buffer \(avWriter.status) \(avWriter.error)")
+                    avReader.cancelReading() // cancel reading
                     completedOrFailed = true
                 }
             }

convert_to_text.m

@@ -29,9 +29,9 @@ function convert_to_text(fn, mat)
 
 fprintf(fh, '# AUTOMATICALLY GENERATED SYLLABLE DETECTOR CONFIGURATION\n');
 fprintf(fh, 'samplingRate = %.1f\n', f.samplerate);
-fprintf(fh, 'windowLength = %d\n', f.win_size);
 fprintf(fh, 'fourierLength = %d\n', f.fft_size);
-fprintf(fh, 'fourierOverlap = %d\n', f.fft_size - f.fft_time_shift);
+fprintf(fh, 'windowLength = %d\n', f.win_size);
+fprintf(fh, 'windowOverlap = %d\n', f.fft_size - f.fft_time_shift);
 
 fprintf(fh, 'freqRange = %.1f, %.1f\n', f.freq_range(1), f.freq_range(end));
 fprintf(fh, 'timeRange = %d\n', f.time_window_steps);