fix: adjust pitch, not just speed

app/src/main/cpp/PlaybackEngine.cpp

@@ -231,7 +231,9 @@ void PlaybackEngine::musicFeedThread() {
         }
 
         if(haveTimeRatio.load()) {
-            stretcher.setTimeRatio(timeRatio.load());
+            double ratio = timeRatio.load();
+            stretcher.setTimeRatio(ratio);
+            stretcher.setPitchScale(ratio);
             haveTimeRatio.store(false);
         }
 
@@ -313,6 +315,7 @@ void PlaybackEngine::musicFeedThread() {
             // next iteration will play silence
             closeMusicFile();
             stretcher.setTimeRatio(1.0); // buffer size for playing silence is computed from 'playbackRate', so reset timeRatio
+            stretcher.setPitchScale(1.0);
             stretcher.process(buf_ptr, 0, true); // set end of playback
             mPlayer->stopAudio();
             continue;
@@ -322,6 +325,7 @@ void PlaybackEngine::musicFeedThread() {
             LOGI("finished reading mp3 file (MPG123_DONE)");
             closeMusicFile();
             stretcher.setTimeRatio(1.0); // buffer size for playing silence is computed from 'playbackRate', so reset timeRatio
+            stretcher.setPitchScale(1.0);
             stretcher.process(buf_ptr, 0, true); // set end of playback
             mPlayer->stopAudio();
             continue;

app/src/main/java/at/lockstep/app/LstForegroundService.java

@@ -259,6 +259,8 @@ public class LstForegroundService extends Service implements SensorEventListener
         stepDetector.filter(event.timestamp, event.values);
         // collect accelerometer recording - adjust timebase to 0.0 sec beginning
         recording.add(new SensorData(event.timestamp - recordingStartTime, event.values));
+        // TODO: acquires at 8 ms intervals ... 125 Hz?!
+        // TODO: must compute actual sampling rate. and either downsample, or adapt the IIR filter parameters. (& length??) - easier to resample.
     }
 
     @Override