How to record sound using the iPhone microphone

How-to by Jim Bentley, Portland Maine - james.bentley@live.com

This is a quick tutorial on how to record sound using the iPhone microphone/headset microphone.  There are a lot of possible variables to sound recording - File output types, bit rates, channels are just a few.

For more information on recording sound and the various formats available, you should see the following page on the AVAudiorecorder class:

http://developer.apple.com/iphone/library/documentation/AVFoundation/Reference/AVAudioRecorder_ClassReference/Reference/Reference.html

Below is the 'main' class of a quick and dirty application to create sound files (uncompressed PCM Wav Files to be exact) inside the application's tmp directory.

 
using System;
using System.Collections.Generic;
using System.Linq;
using MonoTouch.Foundation;
using MonoTouch.UIKit;
using MonoTouch.AudioToolbox;
using MonoTouch.AVFoundation;
using System.IO;


namespace TestRecord
{
    public class Application
    {
        static void Main (string[] args)
        {
            UIApplication.Main (args);
        }
    }
    
    // The name AppDelegate is referenced in the MainWindow.xib file.
    public partial class AppDelegate : UIApplicationDelegate
    {
        //declare AVAudioRecorder recorder
        public AVAudioRecorder recorder;
       
        // This method is invoked when the application has loaded its UI and its ready to run
        public override bool FinishedLaunching (UIApplication app, NSDictionary options)                
           
        {
            // If you have defined a view, add it here:
            // window.AddSubview (navigationController.View);
           
            window.MakeKeyAndVisible ();
            
        //Record Button Delegate
        recordButton.TouchUpInside += delegate {
               
                StartRecording();
                                           
        };
       
        //Stop Button Delegate
        stopButton.TouchUpInside += delegate {
               
                StopRecording();    
               
            };
                   
            return true;
        }
       
        //public void start Recording
        public void StartRecording ()
        {
            NSObject[] values = new NSObject[]
            {    
                NSNumber.FromFloat(44100.0f),
                NSNumber.FromInt32((int)AudioFileType.WAVE),
                NSNumber.FromInt32(1),
                NSNumber.FromInt32((int)AVAudioQuality.Max)
            };

            NSObject[] keys = new NSObject[]
            {
                AVAudioSettings.AVSampleRateKey,
                AVAudioSettings.AVFormatKey,
                AVAudioSettings.AVNumberOfChannelsKey,
                AVAudioSettings.AVEncoderAudioQualityKey
            };

            NSDictionary settings = NSDictionary.FromObjectsAndKeys (values, keys);
           
            //Declare string for application temp path and tack on the file extension
            string fileName = testTextField.Text + ".wav";
            string basedir = Path.Combine (Environment.GetFolderPath (Environment.SpecialFolder.Personal), "..");
            string tmpdir = Path.Combine(basedir, "tmp");
            string audioFilePath = Path.Combine(tmpdir, fileName);
            string tempRecording = audioFilePath;
           
           
            Console.WriteLine(audioFilePath);
            NSUrl url = NSUrl.FromFilename(tempRecording);
           
           
            NSError error = new NSError ();
           
            //Set recorder parameters
            recorder = new AVAudioRecorder (url, settings, error);
           
            //Set Metering Enabled so you can get the time of the wav file
            recorder.MeteringEnabled = true;
            
            recorder.PrepareToRecord();            
            recorder.Record();
                               
        }
    
        //public void stop Recording
        public void StopRecording ()
        {
            recorder.Stop();
           
             recorder.FinishedRecording += delegate {
                recorder.Dispose();
                Console.WriteLine("Done Recording");
            };
           
        }
       
        // This method is required in iPhoneOS 3.0
        public override void OnActivated (UIApplication application)
        {
        }
           
    }
}