First commit, audio echo detection, also changed scope to show last buffer played rather than next buffer to play.

interface/src/Audio.cpp

@@ -105,10 +105,19 @@ int audioCallback (const void *inputBuffer,
     AudioData *data = (AudioData *) userData;
     
     int16_t *inputLeft = ((int16_t **) inputBuffer)[0];
+    int16_t *outputLeft = ((int16_t **) outputBuffer)[0];
+    int16_t *outputRight = ((int16_t **) outputBuffer)[1];
+
+    // Compare the input and output streams to look for correlation
+    data->analyzeEcho(inputLeft, outputLeft, BUFFER_LENGTH_SAMPLES);
     
     // Add Procedural effects to input samples
     data->addProceduralSounds(inputLeft, BUFFER_LENGTH_SAMPLES);
     
+    // add data to the scope
+    scope->addSamples(1, outputLeft, PACKET_LENGTH_SAMPLES_PER_CHANNEL);
+    scope->addSamples(2, outputRight, PACKET_LENGTH_SAMPLES_PER_CHANNEL);
+
     if (inputLeft != NULL) {
         
         //  Measure the loudness of the signal from the microphone and store in audio object
@@ -169,10 +178,7 @@ int audioCallback (const void *inputBuffer,
             data->audioSocket->send((sockaddr *)&audioMixerSocket, dataPacket, BUFFER_LENGTH_BYTES + leadingBytes);
         }
     }
-    
+        
-    int16_t *outputLeft = ((int16_t **) outputBuffer)[0];
-    int16_t *outputRight = ((int16_t **) outputBuffer)[1];
-    
     memset(outputLeft, 0, PACKET_LENGTH_BYTES_PER_CHANNEL);
     memset(outputRight, 0, PACKET_LENGTH_BYTES_PER_CHANNEL);
 
@@ -265,11 +271,7 @@ int audioCallback (const void *inputBuffer,
                 outputLeft[s] = leftSample;
                 outputRight[s] = rightSample;
             }
-            
+                        
-            // add data to the scope
-            scope->addSamples(1, outputLeft, PACKET_LENGTH_SAMPLES_PER_CHANNEL);
-            scope->addSamples(2, outputRight, PACKET_LENGTH_SAMPLES_PER_CHANNEL);
-            
             ringBuffer->setNextOutput(ringBuffer->getNextOutput() + PACKET_LENGTH_SAMPLES);
             
             if (ringBuffer->getNextOutput() == ringBuffer->getBuffer() + RING_BUFFER_SAMPLES) {
@@ -278,6 +280,13 @@ int audioCallback (const void *inputBuffer,
         }
     }
     
+    if (randFloat() < 0.01) {
+        printLog("Ping!\n");
+        for (int i = 0; i < BUFFER_LENGTH_SAMPLES; i++) {
+            outputLeft[i] = (int16_t) (cosf((float)i / 8.f * 2000.f));
+        }
+    }
+
     gettimeofday(&data->lastCallback, NULL);
     return paContinue;
 }

interface/src/AudioData.cpp

@@ -44,5 +44,36 @@ void AudioData::addProceduralSounds(int16_t* inputBuffer, int numSamples) {
     return;
 }
 
+void AudioData::analyzeEcho(int16_t* inputBuffer, int16_t* outputBuffer, int numSamples) {
+    //  Compare output and input streams, looking for evidence of correlation needing echo cancellation
+    //  
+    //  OFFSET_RANGE tells us how many samples to vary the analysis window when looking for correlation,
+    //  and should be equal to the largest physical distance between speaker and microphone, where
+    //  OFFSET_RANGE =  1 / (speedOfSound (meters / sec) / SamplingRate (samples / sec)) * distance
+    //
+    const int OFFSET_RANGE = 10;
+    const int SIGNAL_FLOOR = 1000;
+    float correlation[2 * OFFSET_RANGE + 1];
+    int numChecked = 0;
+    bool foundSignal = false;
+    for (int offset = -OFFSET_RANGE; offset <= OFFSET_RANGE; offset++) {
+        for (int i = 0; i < numSamples; i++) {
+            if ((i + offset >= 0) && (i + offset < numSamples)) {
+                correlation[offset + OFFSET_RANGE] +=
+                            (float) abs(inputBuffer[i] - outputBuffer[i + offset]);
+                numChecked++;
+                foundSignal |= (inputBuffer[i] > SIGNAL_FLOOR);
+            }
+        }
+        correlation[offset + OFFSET_RANGE] /= numChecked;
+        numChecked = 0;
+        if (foundSignal) {
+            printLog("%4.2f, ", correlation[offset + OFFSET_RANGE]);
+        }
+    }
+    if (foundSignal) printLog("\n");
+}
+
+
 
 #endif

interface/src/AudioData.h

@@ -43,8 +43,9 @@ class AudioData {
         void setLastVelocity(glm::vec3 v) { _lastVelocity = v; };
         void setLastAcceleration(glm::vec3 a) { _lastAcceleration = a; };
         void addProceduralSounds(int16_t* inputBuffer, int numSamples);
+        void analyzeEcho(int16_t* inputBuffer, int16_t* outputBuffer, int numSamples);
     
-    private: 
+    private:
         glm::vec3 _lastVelocity;
         glm::vec3 _lastAcceleration;