iPhone App Pick Up Sound

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. 开发者_如何学C 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.

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.

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.