how to monitor audio input on ios using swift - example? - ios

Question

I want to write a simple app that 'does something' when the sound level at the mic reaches a certain level, showing the audio input levels for extra credit
cant find any examples in swift that get to this -- dont want to record, just monitor
have been checking out the docs on the AVFoundation classes but cant get off the ground
thanks

Answer 1

Let you can use below code :
func initalizeRecorder ()
{
do {
try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayAndRecord)
try AVAudioSession.sharedInstance().setActive(true)
}catch{
print(error);
}
let stringDir:NSString = self.getDocumentsDirectory();
let audioFilename = stringDir.stringByAppendingPathComponent("recording.m4a")
let audioURL = NSURL(fileURLWithPath: audioFilename)
print("File Path : \(audioFilename)");
// make a dictionary to hold the recording settings so we can instantiate our AVAudioRecorder
let settings = [
AVFormatIDKey: Int(kAudioFormatMPEG4AAC),
AVSampleRateKey: 12000.0,
AVNumberOfChannelsKey: 1 as NSNumber,
AVEncoderBitRateKey:12800 as NSNumber,
AVLinearPCMBitDepthKey:16 as NSNumber,
AVEncoderAudioQualityKey: AVAudioQuality.High.rawValue
]
do {
if audioRecorder == nil
{
audioRecorder = try AVAudioRecorder(URL: audioURL, settings: settings )
audioRecorder!.delegate = self
audioRecorder!.prepareToRecord();
audioRecorder!.meteringEnabled = true;
}
audioRecorder!.recordForDuration(NSTimeInterval(5.0));
} catch {
print("Error")
}
}
//GET DOCUMENT DIR PATH
func getDocumentsDirectory() -> String {
let paths = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)
let documentsDirectory = paths[0]
return documentsDirectory
}
////START RECORDING
#IBAction func btnStartPress(sender: AnyObject) {
recordingSession = AVAudioSession.sharedInstance()
do {
recordingSession.requestRecordPermission() { [unowned self] (allowed: Bool) -> Void in
dispatch_async(dispatch_get_main_queue()) {
if allowed {
print("Allowd Permission Record!!")
self.initalizeRecorder ()
self.audioRecorder!.record()
//instantiate a timer to be called with whatever frequency we want to grab metering values
self.levelTimer = NSTimer.scheduledTimerWithTimeInterval(0.02, target: self, selector: Selector("levelTimerCallback"), userInfo: nil, repeats: true)
} else {
// failed to record!
self.showPermissionAlert();
print("Failed Permission Record!!")
}
}
}
} catch {
// failed to record!
print("Failed Permission Record!!")
}
}
//This selector/function is called every time our timer (levelTime) fires
func levelTimerCallback() {
//we have to update meters before we can get the metering values
if audioRecorder != nil
{
audioRecorder!.updateMeters()
let ALPHA : Double = 0.05;
let peakPowerForChannel : Double = pow(Double(10.0), (0.05) * Double(audioRecorder!.peakPowerForChannel(0)));
lowPassResults = ALPHA * peakPowerForChannel + Double((1.0) - ALPHA) * lowPassResults;
print("low pass res = \(lowPassResults)");
if (lowPassResults > 0.7 ){
print("Mic blow detected");
}
}
}
//STOP RECORDING
#IBAction func btnStopPress(sender: AnyObject) {
if audioRecorder != nil
{
audioRecorder!.stop()
self.levelTimer.invalidate()
}
}

Answer 2

In AVAudioRecorder you can "record audio" (you don't have to save it) and set meteringEnabled to use the function peakPowerForChannel(_:)
It will
Returns the peak power for a given channel, in decibels, for the sound being recorded.
This link may provide a sample code.
Let me know if it help you.