Add comments to explain the the phase offset usage.

google · Mar 12, 2024 · 570c661 · 570c661
1 parent 83803e5
commit 570c661
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Showing 2 changed files with 12 additions and 4 deletions.
diff --git a/apps/OboeTester/app/src/main/cpp/analyzer/BaseSineAnalyzer.h b/apps/OboeTester/app/src/main/cpp/analyzer/BaseSineAnalyzer.h
@@ -211,8 +211,16 @@ class BaseSineAnalyzer : public LoopbackProcessor {
     double  mPhaseIncrement = 0.0;
     double  mOutputPhase = 0.0;
     double  mOutputAmplitude = 0.75;
+    // This is the phase offset between the output sine wave and the recorded
+    // signal at the tuned frequency.
     // If this jumps around then we are probably just hearing noise.
+    // Noise can cause the magnitude to be high but mPhaseOffset will be pretty random.
+    // If we are tracking a sine wave then mPhaseOffset should be consistent.
     double  mPhaseOffset = 0.0;
+    // kPhaseInvalid indicates that the phase measurement cannot be used.
+    // We were seeing times when a magnitude of zero was causing atan2(s,c) to
+    // return a phase of zero, which looked valid to Java. This is a way of passing
+    // an error code back to Java as a single value to avoid race conditions.
     static constexpr double kPhaseInvalid = -999.0;
     double  mMagnitude = 0.0;
     static constexpr double kMinValidMagnitude = 2.0 / (1 << 16);

diff --git a/apps/OboeTester/app/src/main/java/com/mobileer/oboetester/WaveformView.java b/apps/OboeTester/app/src/main/java/com/mobileer/oboetester/WaveformView.java
@@ -77,9 +77,9 @@ private void init() {
     protected void onSizeChanged(int w, int h, int oldw, int oldh) {
         mCurrentWidth = w;
         mCurrentHeight = h;
-        mOffsetY = 0.5f * h;
+        mOffsetY = 0.5f * h; // Center waveform vertically in the viewport.
         // Scale down so that we can see the top of the waveforms if they are clipped.
-        mScaleY = 0.95f * (0.0f - mOffsetY);
+        mScaleY = -0.95f * mOffsetY; // Negate so positive values are on top.
     }
 
     public String getMessage() {
@@ -122,8 +122,8 @@ protected void onDraw(Canvas canvas) {
         float x0 = 0.0f;
         if (xScale < 1.0) {
             // Draw a vertical bar for multiple samples.
-            float ymin = mOffsetY;
-            float ymax = mOffsetY;
+            float ymin = mOffsetY; // vertical center
+            float ymax = mOffsetY; // vertical center
             for (int i = 0; i < mSampleCount; i++) {
                 float x1 = i * xScale;
                 if ((int) x0 != (int) x1) {