Get frequency of a sound recorder with microphone

Question

I need to calculate the frequency, in Hertz, of a sound recorded with the microphone. What I'm doing now is using AVAudioRecorder to listen to the mic, with a timer that call a specific function every 0.5 seconds. Here some code :

class ViewController: UIViewController {
    
    var audioRecorder: AVAudioRecorder?
    var timer: Timer?

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        
        let permission = AVAudioSession.sharedInstance().recordPermission
        
        if permission == AVAudioSession.RecordPermission.undetermined {
            
            AVAudioSession.sharedInstance().requestRecordPermission { (granted) in
                if granted {
                    print("Permission granted!")
                } else {
                    print("Permission not granted!")
                }
            }
        } else if permission == AVAudioSession.RecordPermission.granted {
            
            do {
                try AVAudioSession.sharedInstance().setCategory(AVAudioSession.Category.record)
                
                let settings = [
                    AVSampleRateKey: 44100.0,
                    AVFormatIDKey: kAudioFormatAppleLossless,
                    AVNumberOfChannelsKey: 1,
                    AVEncoderAudioQualityKey: AVAudioQuality.max
                ] as [String : Any]
                
                audioRecorder = try AVAudioRecorder.init(url: NSURL.fileURL(withPath: "dev/null"), settings: settings)
                audioRecorder?.prepareToRecord()
                audioRecorder?.isMeteringEnabled = true
                audioRecorder?.record()
                
                timer = Timer.scheduledTimer(
                    timeInterval: 0.5,
                    target: self,
                    selector: #selector(analyze),
                    userInfo: nil,
                    repeats: true
                )
            } catch (let error) {
                print("Error! \(error.localizedDescription)")
            }
        }
    }


    @objc func analyze() {
        
        audioRecorder?.updateMeters()
        
        let peak = audioRecorder?.peakPower(forChannel: 0)
        
        print("Peak : \(peak)")
        
        audioRecorder?.updateMeters()
    }
}

I do not know how to get the frequency of the sound in hertz. It's fine also to use a 3rd party framework for me.

Thanks.

Answer 1

Any given recorded sound will not have a single frequency. It will have a mix of frequencies at different amplitudes.

You need to do frequency analysis on the input sounds, usually using FFT (Fast Fourier Transforms) on the audio data.

A google search revealed this article on doing frequency analysis using the Accelerate framework:

http://www.myuiviews.com/2016/03/04/visualizing-audio-frequency-spectrum-on-ios-via-accelerate-vdsp-fast-fourier-transform.html