gistfile1.cs

using System;
using MonoTouch.UIKit;
using MonoTouch.Foundation;
using MonoTouch.AVFoundation;
using MonoTouch.CoreAnimation;
using MonoTouch.ObjCRuntime;
using System.Threading;
using System.IO;

namespace MyProject {
	public partial class MyViewController : UIViewController {
		private AVAudioRecorder recorder;

		public override void ViewDidLoad () {
			base.ViewDidLoad ();

			NSError error;

			var url =  NSUrl.FromFilename ("/dev/nulasdl");

			var values = new NSObject[]
			{
				NSNumber.FromFloat ((float)44100), //Sample Rate
				NSNumber.FromInt32 ((int)MonoTouch.AudioToolbox.AudioFormatType.AppleLossless), //AVFormat
				NSNumber.FromInt32 (2),
				NSNumber.FromInt32 ((int)MonoTouch.AVFoundation.AVAudioQuality.Min)
			};

			var keys = new NSObject[]
			{
				AVAudioSettings.AVSampleRateKey,
				AVAudioSettings.AVFormatIDKey,
				AVAudioSettings.AVNumberOfChannelsKey,
				AVAudioSettings.AVEncoderAudioQualityKey
			};
			//var audioSettings = NSDictionary.FromObjectsAndKeys (values, keys);
			//recorder = new AVAudioRecorder (url, audioSettings, out error);
			var audioSettings = new AudioSettings (NSDictionary.FromObjectsAndKeys (values, keys));
			recorder = AVAudioRecorder.Create(url, audioSettings, out error);
			if (error == null) {
				var session = AVAudioSession.SharedInstance ();
				session.SetCategory (AVAudioSession.CategoryRecord);

				recorder.PrepareToRecord ();
				recorder.MeteringEnabled = true;

				recorder.Record ();

				CADisplayLink displayLink = CADisplayLink.Create (this, new Selector ("UpdateMetersSelector"));
				displayLink.AddToRunLoop (NSRunLoop.Current, NSRunLoop.NSRunLoopCommonModes);
			} else {
				Console.WriteLine ("Error...");
				return;
			}
		}

		[Export ("UpdateMetersSelector")]
		private void UpdateMeters()
		{
			recorder.UpdateMeters();
			Console.WriteLine(recorder.AveragePower (0));
		}
	}
}

gistfile2.txt

//
//  ViewController.m
//  24364-xamarinbug
//
//  Created by Alexander Andronov on 28/11/14.
//  Copyright (c) 2014 Alexander Andronov. All rights reserved.
//

#import "ViewController.h"
#import <AVFoundation/AVFoundation.h>

@interface ViewController ()

@property (nonatomic, strong) AVAudioRecorder *recorder;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    NSURL *url = [NSURL fileURLWithPath:@"/dev/nulasdsl"];
    
    NSDictionary *settings = @{AVSampleRateKey:          [NSNumber numberWithFloat: 44100.0],
                               AVFormatIDKey:            [NSNumber numberWithInt: kAudioFormatAppleLossless],
                               AVNumberOfChannelsKey:    [NSNumber numberWithInt: 2],
                               AVEncoderAudioQualityKey: [NSNumber numberWithInt: AVAudioQualityMin]};
    
    NSError *error;
    self.recorder = [[AVAudioRecorder alloc] initWithURL:url settings:settings error:&error];
    
    if(error) {
        NSLog(@"Ups, could not create recorder %@", error);
        //return;
    }
    
    [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayAndRecord error:&error];
    
    if (error) {
        NSLog(@"Error setting category: %@", [error description]);
    }
    
    [self.recorder prepareToRecord];
    [self.recorder setMeteringEnabled:YES];
    [self.recorder record];
    
    CADisplayLink *displaylink = [CADisplayLink displayLinkWithTarget:self selector:@selector(updateMeters)];
    [displaylink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];
}


- (void)updateMeters
{
    [self.recorder updateMeters];
    
    float power = [self.recorder averagePowerForChannel:0];
    NSLog([NSString stringWithFormat: @"%f", power]);
}

@end