Error checks and comments

main.cpp

@@ -25,6 +25,7 @@ typedef struct {
     PmStream* pmStream;
 } State;
 
+// PortAudio callback for audio I/O
 static int paCallback(
         const void *inputBuffer,
         void *outputBuffer,
@@ -53,6 +54,7 @@ static int paCallback(
     return 0;
 }
 
+// PortTimer callback for MIDI I/O
 static void ptCallback(PtTimestamp timestamp, void* userData) {
     State* state = (State*) userData;
     PmEvent events[8];
@@ -116,6 +118,7 @@ int main(void) {
     state.filter.setQ(1);
     state.time = 0;
 
+    // Initialise PortMIDI and PortAudio libraries
     PmError pmErr = Pm_Initialize();
     if(pmErr != pmNoError) {
         handlePMError(pmErr);
@@ -134,17 +137,18 @@ int main(void) {
         }
         cout << i << ". " << deviceInfo->name << endl;
     }
-
     int pmDeviceIndex;
-    for(;;) {
+    for(;;) { // loop for input until valid choice is made
         string input;
         getline(cin, input);
         try {
             pmDeviceIndex = stoi(input);
-            if(pmDeviceIndex >= 0 && pmDeviceIndex < pmDeviceCount) {
+            if(     pmDeviceIndex >= 0 &&
+                    pmDeviceIndex < pmDeviceCount &&
+                    Pm_GetDeviceInfo(pmDeviceIndex)->input) {
                 break;
             }
-        } catch(...) { }
+        } catch(...) { } // stoi() throws an exeption for invalid integers
         cout << "Invalid selection" << endl;   
     }
 
@@ -158,32 +162,34 @@ int main(void) {
         cout << i << ". " << deviceInfo->name << " (" << Pa_GetHostApiInfo(deviceInfo->hostApi)->name << ")" << endl;
     }
     PaHostApiIndex paDeviceIndex;
-    for(;;) {
+    for(;;) { // loop for input until valid choice is made
         string input;
         getline(cin, input);
         try {
             paDeviceIndex = stoi(input);
-            if(paDeviceIndex >= 0 && paDeviceIndex < paDeviceCount) {
+            if(     paDeviceIndex >= 0 &&
+                    paDeviceIndex < paDeviceCount &&
+                    Pa_GetDeviceInfo(paDeviceIndex)->maxOutputChannels >= 2) {
                 break;
             }
-        } catch(...) { }
+        } catch(...) { } // stoi() throws an exeption for invalid integers
         cout << "Invalid selection" << endl;   
     }
 
+    // Start MIDI timer and open MIDI input
     Pt_Start(1, ptCallback, &state);
-
     PmError pmError = Pm_OpenInput(
         &state.pmStream,
         pmDeviceIndex,
         NULL,
-        256,
+        8,
         NULL,
         NULL);
     if(pmErr != pmNoError) {
         handlePMError(pmErr);
     }
 
-    /* Open an audio I/O stream. */
+    // Configure/start audio output stream
     PaStream *paStream;
     PaStreamParameters paStreamParams;
     paStreamParams.device = paDeviceIndex;
@@ -193,17 +199,16 @@ int main(void) {
     paStreamParams.hostApiSpecificStreamInfo = NULL;
     paErr = Pa_OpenStream(
         &paStream,
-        NULL,           /* no input channels */
-        &paStreamParams,  /* stereo output */
+        NULL,               /* no input channels */
+        &paStreamParams,    /* stereo output */
         SAMPLE_RATE,
-        0,              /* frames per buffer */
+        0,                  /* frames per buffer */
         paNoFlag,
         paCallback,
         &state);
     if(paErr != paNoError) {
         handlePAError(paErr);
     }
-
     paErr = Pa_StartStream(paStream);
     if(paErr != paNoError) { 
         handlePAError(paErr);
@@ -212,7 +217,7 @@ int main(void) {
     const PaStreamInfo *paStreamInfo = Pa_GetStreamInfo(paStream);
     cout << "Latency: " << round(1000 * paStreamInfo->outputLatency) << " ms" << endl;
 
-    /* Wait for Return key */
+    // Wait for Return key
     cout << "Running - press Enter to exit" << endl;
     getchar();
 

oscillator.h

@@ -11,9 +11,9 @@ public:
     enum Mode { MODE_SINE, MODE_SAW, MODE_SQUARE };
 
     Mode mode;
-    float phase;
-    float phaseStep;
-    float value;
+    float phase;        // current waveform phase angle (radians)
+    float phaseStep;    // phase angle step per sample
+    float value;        // current amplitude value
 
     Oscillator();
 
@@ -41,7 +41,7 @@ public:
         else return 0.0;
     }
 
-    // This class provides a band-limited oscillator
+    // Generate next output sample and advance the phase angle
     float tick() {
         float t = phase / PIx2; // Define half phase
         
@@ -61,10 +61,10 @@ public:
         }
 
         phase += phaseStep;
-        if(phase >= PIx2) {
+        if(phase >= PIx2) { // wrap if phase angle >=360º
             phase -= PIx2;
         }
         
-        return value; // Output
+        return value;
     }
 };

svf.h

@@ -18,11 +18,11 @@ protected:
 
 public:
     typedef struct {
-        float hp;
-        float bp;
-        float lp;
-        float br;
-        float ap;
+        float hp;   // high-pass
+        float bp;   // band-pass
+        float lp;   // low-pass
+        float br;   // band-reject
+        float ap;   // all-pass
     } Output;
 
     SVF() {