In AudioMonitor, the code for producing Mac direct mode audio was substantially revised. The Novocaine code for audio output was removed. AudioMonitor now uses Apple's AudioConverter and AudioQueue services to resample audio to 48000 Hz (compared to 44100 with Novocaine). TPCircularBuffer was added and used for a couple of buffers. The first buffer stores the original LPCM audio data from the RTL-SDR USB device. That buffer is also used as the input for the AudioConverter to resample the LPCM. The second buffer stores the output after the data is resampled, which is used as input to the AudioQueue for playback on the currently selected system audio device, usually the Mac speakers. Most of the processing occurs on threads threads. The first thread gets the RTL-SDR data and stores it to the first buffer. The second thread resamples the audio and stores it to the second buffer. The third thread retrieves the resampled data and renders it to audio.

In the initial test, AudioMonitor is running with about 2% CPU utilization.

A known problem is that audio resampled from a lower source rate than 48000 Hz has buffering problems when using Icecast playback, that problem will be investigated and fixed.

The project version was incremented to 1.11.

Author: dsward2

AudioMonitor/AudioMonitor.xcodeproj/project.pbxproj

@@ -8,31 +8,45 @@
 
 #import <Foundation/Foundation.h>
 
-#import "Novocaine.h"
-#import "RingBuffer.h"
+#import <AudioToolbox/AudioToolbox.h>
+#import <Accelerate/Accelerate.h>
+//#import "TPCircularBuffer+AudioBufferList.h"
+#import "TPCircularBuffer.h"
 
 
+// AudioQueue values
+#define kAudioQueueBuffersCount 3
+
 @interface AudioMonitor : NSObject
 {
-    AudioConverterRef inAudioConverter;
+    AudioConverterRef inAudioConverter;     // AudioConverter for resampling PCM data to 48000 Hz
+
+    AudioStreamBasicDescription audioConverterInputDescription;
+    AudioStreamBasicDescription audioConverterOutputDescription;
 
-    AudioStreamBasicDescription inputDescription;
-    AudioStreamBasicDescription outputDescription;
+    AudioBuffer audioConverterInputAudioBuffer;
+    UInt64 audioConverterInputBufferOffset;
+    UInt32 audioConverterInputPacketsRemain;
 
-    AudioBuffer inputAudioBuffer;
-    UInt64 inputBufferOffset;
-    UInt32 inputPacketsRemain;
+    TPCircularBuffer inputCircularBuffer;        // TPCircularBuffer for storage and retrieval of input PCM data from stdin
+    TPCircularBuffer audioConverterCircularBuffer;        // TPCircularBuffer for storage and retrieval of resampled PCM data
 
-    AudioBufferList outputBufferList;
-    void * outputBufferPtr;
-    UInt32 outputBytes;
+    AudioBufferList audioConverterOutputBufferList;
+    void * audioConverterOutputBufferPtr;
+    UInt32 audioConverterOutputBytes;
+
+    AudioQueueRef audioQueue;               // AudioQueue for playing resampled PCM data to current audio output device, usually speakers
+    
+    AudioStreamBasicDescription audioQueueDescription;
+    AudioQueueBufferRef buffers[kAudioQueueBuffersCount];
+    NSUInteger audioQueueIndex;
 }
 
-@property (nonatomic, strong) Novocaine * audioManager;
 @property (assign) NSInteger sampleRate;
 @property (assign) float volume;
 
 
+
 - (void)runAudioMonitorWithSampleRate:(NSInteger)sampleRate volume:(float)volume;
 - (void)convertBuffer:(void *)inputBufferPtr length:(UInt32)dataLength;