To record sound with iOS 7 use AVAudioRecorder class.

Before stert the recording with the record method call the prepareToRecord method. Both methods return a boolean like return value. It’s important to check that returns YES. In order case show an error because the recording won’t start.

Creation and configuration of AVAudioRecorder

The object AVAudioRecorder requires for its initialization an object of type NSDictionary with the following values:

@{AVFormatIDKey:@(kAudioFormatMPEG4AAC),
  AVSampleRateKey:@44100.0,
  AVNumberOfChannelsKey:@2,
  AVEncoderAudioQualityKey:@(AVAudioQualityMin),
  AVEncoderBitRateKey:@16,
};

Also create this object NSDictionary is needed to make the previous step: create an AVAudioSesion object.

Since iOS 7 is needed to create an AVAudioSession** object before the creation of **AVAudioRecorder8. In other case recording won’t start.

Code sample

//
//  ViewController.m
//  NoiseAlertPrototype
//
//  Created by Daniel Vela on 30/01/14.
//  Copyright (c) 2014 veladan. All rights reserved.
//

#import "ViewController.h"

const float min_level = 20.0f;
const float max_level = 160.0f;

@interface ViewController ()

@end

@implementation ViewController

-(AVAudioRecorder*)recorder {
    if (_recorder == nil) {
        NSURL* url = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory
                                                             inDomains:NSUserDomainMask]
                      lastObject];
        url = [url URLByAppendingPathComponent:@"record.aac"];
        NSDictionary* settings = @{AVFormatIDKey:@(kAudioFormatMPEG4AAC),
                                   AVSampleRateKey:@44100.0,
                                   AVNumberOfChannelsKey:@2,
                                   AVEncoderAudioQualityKey:@(AVAudioQualityMin),
                                   AVEncoderBitRateKey:@16,

                                   };
        AVAudioSession *audioSession = [AVAudioSession sharedInstance];
        [audioSession setCategory:AVAudioSessionCategoryRecord
                            error:nil];
        NSError* error;
        _recorder = [[AVAudioRecorder alloc] initWithURL:url
                                                    settings:settings
                                                       error:&error];
        if (error) {
            UIAlertView* alert = [[UIAlertView alloc] initWithTitle:@"Error creating audio recorder"
                                                            message:[error description]
                                                           delegate:nil
                                                  cancelButtonTitle:@"cancel"
                                                  otherButtonTitles:nil];
            [alert show];
        }
        _recorder.meteringEnabled = YES;

    }
    return _recorder;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    [self setStop];
    [self startTakingNoiseSamples];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

float adjustNoiseLevel(float value) {
    if (value > 0) value = 0;
    value = max_level + value;
    value = value / max_level;
    return value;
}

- (void)setAverageLevelValue:(float)value {
    value = adjustNoiseLevel(value);
    [self.averageLevel setProgress:value];
}

- (void)setPeakLevelValue:(float)value  {
    value = adjustNoiseLevel(value);
    [self.peakLevel setProgress:value];
}

- (void)startTakingNoiseSamples {

    if ([self.recorder isRecording] == YES) {
        [self.recorder updateMeters];
        float averagePower = [self.recorder averagePowerForChannel:0];
        float peakPower = [self.recorder peakPowerForChannel:0];
        [self setAverageLevelValue:averagePower];
        [self setPeakLevelValue:peakPower];
    }

    [self performSelector:@selector(startTakingNoiseSamples)
               withObject:nil
               afterDelay:0.05f];
}

- (void)startRecording {
    [self setStart];
    BOOL prepared = [self.recorder prepareToRecord];
    if (prepared == NO) {
        UIAlertView* alert = [[UIAlertView alloc] initWithTitle:@"Error creating audio recorder"
                                                        message:@"no preparado"
                                                       delegate:nil
                                              cancelButtonTitle:@"cancel"
                                              otherButtonTitles:nil];
        [alert show];

    }
    BOOL started = [self.recorder record];
    if (started == NO) {
        UIAlertView* alert = [[UIAlertView alloc] initWithTitle:@"Error starting recording"
                                                        message:@"no preparado"
                                                       delegate:nil
                                              cancelButtonTitle:@"cancel"
                                              otherButtonTitles:nil];
        [alert show];

    }

}

- (void)stopRecording {
    [self setStop];
    [self.recorder stop];
}

- (void)setStop {
    [self.startStopButton setTitle:@"Start" forState:UIControlStateNormal];
    [self.startStopButton addTarget:self
                          action:@selector(startRecording)
                forControlEvents:UIControlEventTouchUpInside];
}

- (void)setStart {
    [self.startStopButton setTitle:@"Stop" forState:UIControlStateNormal];
    [self.startStopButton addTarget:self
                          action:@selector(stopRecording)
                forControlEvents:UIControlEventTouchUpInside];
}


@end

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