IDTMessaging Test

ViewController.m

- (void)prepareToRecordAudio {
    self.lowpassResults = 0.0f;
    
    NSError *error;
    [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayAndRecord error:&error];
    
    // Setup default settings for the recorder
    self.recorder = [[AVAudioRecorder alloc] initWithURL:[self applicationDocumentsDirectory]
                                                            settings:@{
                                                                       AVFormatIDKey : @(kAudioFormatMPEG4AAC),
                                                                       AVSampleRateKey : @(44100.0f),
                                                                       AVNumberOfChannelsKey : @(1),
                                                                       AVEncoderAudioQualityKey : @(AVAudioQualityMax)
                                                                       }
                                                               error:&error];
    [self.recorder prepareToRecord];
    [self.recorder setMeteringEnabled:YES];
    [self startRecordingAudio];
}

- (void)startRecordingAudio {
    [self.recorder record];
    
    self.recordingTimer = [NSTimer scheduledTimerWithTimeInterval:0.1f target:self selector:@selector(updateAverageFrequencyData) userInfo:nil repeats:YES];
    [[NSRunLoop currentRunLoop] addTimer:self.recordingTimer forMode:NSRunLoopCommonModes];
}

- (void)updateAverageFrequencyData {
    [self.recorder updateMeters];
    
    // Apply lowpass filter to current powerPeak data
    const CGFloat kAlpha = 0.05;
    CGFloat currentPeakPower = pow(10, (kAlpha * [self.recorder peakPowerForChannel:0]));
    self.lowpassResults = kAlpha * currentPeakPower + (1.0 - kAlpha) * self.lowpassResults;
    if (self.lowpassResults < 0.1) {
        // Here goes the magic transformation to get Hz frequency.
    }
}