iPhone App Pick Up Sound - iphone

Question

I am trying to do a certain action based on whether or not the user makes a loud sound. I'm not trying to do any voice recognition or anything. Just simply do an action based on whether the iPhone picks up a loud sound.
Any suggestions, tutorials, I can't find anything on the apple developer site. I'm assuming i'm not looking or searching right.

Answer 1

The easiest thing for you do is to use the AudioQueue services. Here's the manual:
Apple AQ manual
Basically, look for any example code that initialized things with AudioQueueNewInput(). Something like this:
Status = AudioQueueNewInput(&_Description,
Audio_Input_Buffer_Ready,
self,
NULL,
NULL,
0,
&self->Queue);
Once you have that going, you can enable sound level metering with something like this:
// Turn on level metering (iOS 2.0 and later)
UInt32 on = 1;
AudioQueueSetProperty(self->Queue,kAudioQueueProperty_EnableLevelMetering,&on,sizeof(on));
You will have a callback routine that is invoked for each chunk of audio data. In it, you can check the current meter levels with something like this:
//
// Check metering levels and detect silence
//
AudioQueueLevelMeterState meters[1];
UInt32 dlen = sizeof(meters);
Status = AudioQueueGetProperty(_Queue,kAudioQueueProperty_CurrentLevelMeterDB,meters,&dlen);
if (Status == 0) {
if (meters[0].mPeakPower > _threshold) {
silence = 0.0; // reset silence timer
} else {
silence += time;
}
}
//
// Notify observers of incoming data.
//
if (delegate) {
[delegate audioMeter:meters[0].mPeakPower duration:time];
[delegate audioData:Buffer->mAudioData size:Buffer->mAudioDataByteSize];
}
Or, in your case, instead of silence you can detect if the decibel level is over a certain value for long enough. Note that the decibel values you will see will range from about -70.0 for dead silence, up to 0.0db for very loud things. On an exponential scale. You'll have to play with it to see what values work for your particular application.

Answer 2

Apple has examples such as Speak Here which looks to have code relating to decibels. I would check some of the meter classes for examples. I have no audio programming experience but hopefully that will get you started while someone provides you with a better answer.