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Swemoph
Swemoph

Reputation: 326

Getting Decibels from AVAudioRecorder

I'm trying to get a decibel value from an AVAudio Recorder. This is my code currently. I have a method to start the recorder, then a method to read the decibel values.

    var recorder: AVAudioRecorder!

Recorder defined globally, then used here:

    func init_recorder() -> Void
{
    let recordersettings = [
        AVFormatIDKey: Int(kAudioFormatAppleIMA4),
        AVSampleRateKey: 44100,
        AVNumberOfChannelsKey: 1 as NSNumber,
        AVLinearPCMBitDepthKey: 16,
        AVLinearPCMIsFloatKey: false,
        AVLinearPCMIsBigEndianKey: false,
        //AVEncoderAudioQualityKey: AVAudioQuality.High.rawValue
    ]
    let filename = NSURL(fileURLWithPath: NSTemporaryDirectory().stringByAppendingString("tmp.caf"))

    do
    {
        recorder = try AVAudioRecorder(URL: filename, settings: recordersettings)
        recorder.meteringEnabled = true
        recorder.prepareToRecord()
        recorder.record()
        recorder.updateMeters()

    }
    catch
    {
        print("error")
    }


}

Then to get the decibel values I have

    func get_decibels() -> Float
{
    recorder.updateMeters()
    return recorder.averagePowerForChannel(0)
}

For some reason this is returning a value of -120.0 every time it is called and i'm not too sure why. I have read from http://b2cloud.com.au/tutorial/obtaining-decibels-from-the-ios-microphone/ and a few other stack overflow threads but most of the examples seem to be quite similar to mine.

Any help appreciated, many thanks!

Upvotes: 3

Views: 2763

Answers (1)

Mikita Manko
Mikita Manko

Reputation: 1113

After you have inited the AVAudioSession

let session = AVAudioSession.sharedInstance()
    try session.setCategory(AVAudioSessionCategoryPlayAndRecord)
    try session.overrideOutputAudioPort(AVAudioSessionPortOverride.speaker)
    try session.setActive(true)
try recorder = AVAudioRecorder(url: getDocumentsDirectory(), settings: settings)

and started recorder

func start() {
    recorder?.record()
    recorder?.updateMeters()
}

You can get the decibels by calling

let decibels = recorder.averagePower(forChannel: 0)

from -120 (min value) up to 0. Noice level of some cafe for example is -20

here's the more detailed example http://www.mikitamanko.com/blog/2017/04/15/swift-how-to-get-decibels/

Upvotes: 1

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