Our question is about an AudioToolbox framework:
In what time interval is measured the "mAveragePower" value in "AudioQueueLevelMeterState struct" ?
Our app shows a decibel value to user.
The code that we use for init an AudioQueue:
fmt.mFormatID = kAudioFormatLinearPCM;
fmt.mSampleRate = 8000.0;
fmt.mChannelsPerFrame = 1;
fmt.mBitsPerChannel = 16;
fmt.mChannelsPerFrame = 1;
fmt.mFramesPerPacket = 1;
fmt.mBytesPerFrame = sizeof (SInt16);
fmt.mBytesPerPacket = sizeof (SInt16);
fmt.mFormatFlags = kLinearPCMFormatFlagIsSignedInteger | kLinearPCMFormatFlagIsPacked;
__block OSStatus status = AudioQueueNewInput (
&fmt,
HandleInputBuffer,
&isWrite,
NULL,
kCFRunLoopCommonModes,
0,
&queue
);
AudioQueueBufferRef buffers[kNumberBuffers];
UInt32 bufferByteSize = kSamplesSize;
for (int i = 0; i < kNumberBuffers; ++i) {
OSStatus allocateStatus;
allocateStatus = AudioQueueAllocateBuffer (
queue,
bufferByteSize,
&buffers[i]
);
OSStatus enqueStatus;
NSLog(@"allocateStatus = %d" , allocateStatus);
enqueStatus = AudioQueueEnqueueBuffer (
queue,
buffers[i],
0,
NULL
);
NSLog(@"enqueStatus = %d" , enqueStatus);
}
UInt32 d = 1;
status = AudioQueueSetProperty (queue, kAudioQueueProperty_EnableLevelMetering, &d, sizeof(UInt32));
NSLog(@"audio enable metrics status = %d" , status);
dispatch_async(dispatch_get_main_queue(), ^{
status = AudioQueueStart (
queue,
NULL
);
NSLog(@"status of audio queue start = %ld" , status);
});
Once in 1/2 second we get metrics with mAveragePower value:
UInt32 dataSize = sizeof(AudioQueueLevelMeterState) * 1 ;
AudioQueueLevelMeterState *levels = (AudioQueueLevelMeterState*)malloc(dataSize);
OSStatus status = AudioQueueGetProperty(queue, kAudioQueueProperty_CurrentLevelMeterDB, levels, &dataSize);
float decibelValue = levels->mAveragePower;
free(levels);
So, as I wrote in beginning, we don't understand on what time interval is computed an average in mAveragePower? If it is computed from last time we asked the metrics (a half second ago) or on some other time interval?
