Changing the Pitch of a Sound

I got a tweet earlier today from some one asking me how to change the pitch of a wave file. The person asking was aware that SoundEffectInstance has a setting to alter pitch but it wasn’t sufficient for his needs. He needed to be able to save the modified WAV to a file. It’s something that is easy to do. So I made a quick example

Video Example

I used a technique that comes close to matching linear interpolation. It get’s the job done but isn’t the best technique because of the opportunity for certain types of distortion to introduced. Methods with less distortion are available at the cost of potentially more CPU cycles. For the example I made no matter what the original sample rate was I am playing back at 44KHz and adjusting my interpolation accordingly so that no unintentional changes in pitch are introduced.

To do the work I’ve created a class named AdjustedSoundEffect. It has a Play() method that takes as it’s argument the factor by which the pitch should be adjusted where 1 plays the sound at the original pitch, 2 plays it at twice its pitch, and 0.5 plays it at half its pitch.

If you are interested the code I used is below.

using System;
using System.IO;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using Microsoft.Xna.Framework.Audio;

namespace J2i.Net.VoiceRecorder.Utility
    public class AdjustedSoundEffect
        //I will always playback at 44KHz regardless of the original sample rate. 
        //I'm making appropriate adjustments to prevent this from resulting in the
        //pitch being shifted. 
        private const int PlaybackSampleRate = 16000;
        private const int BufferSize = PlaybackSampleRate*2;

        private int _channelCount = 1;
        private int _sampleRate;
        private int _bytesPerSample = 16;
        private int _byteCount = 0;
        private float _baseStepRate = 1;
        private float _adjustedStepRate;
        private float _index = 0;
        private int playbackBufferIndex = 0;
        private int _sampleStep = 2;

        private bool _timeToStop = false;

        private byte[][] _playbackBuffers;

        public bool IsPlaying { get; set;  }

        public object SyncRoot = new object();

        private DynamicSoundEffectInstance _dse;

        public static AdjustedSoundEffect FromStream(Stream source)
            var retVal = new AdjustedSoundEffect(source);
            return retVal;

        public AdjustedSoundEffect()
            _playbackBuffers = new byte[3][];
            for (var i = 0; i < _playbackBuffers.Length;++i )
                _playbackBuffers[i] = new byte[BufferSize];
                _dse = new DynamicSoundEffectInstance(PlaybackSampleRate, AudioChannels.Stereo);
            _dse.BufferNeeded += new EventHandler<EventArgs>(_dse_BufferNeeded);

        void SubmitNextBuffer()
            lock (SyncRoot)
                byte[] nextBuffer = _playbackBuffers[playbackBufferIndex];
                playbackBufferIndex = (playbackBufferIndex + 1)%_playbackBuffers.Length;
                int i_step = 0;
                int i = 0;

                int endOfBufferMargin = 2*_channelCount;
                for (;
                    i < (nextBuffer.Length / 4) && (_index < (_sourceBuffer.Length - endOfBufferMargin));
                    ++i, i_step += 4)

                    int k = _sampleStep*(int) _index;
                    if (k > _sourceBuffer.Length - endOfBufferMargin)
                        k = _sourceBuffer.Length -endOfBufferMargin ;
                    nextBuffer[i_step + 0] = _sourceBuffer[k + 0];
                    nextBuffer[i_step + 1] = _sourceBuffer[k + 1];
                    if (_channelCount == 2)
                        nextBuffer[i_step + 2] = _sourceBuffer[k + 2];
                        nextBuffer[i_step + 3] = _sourceBuffer[k + 3];
                        nextBuffer[i_step + 2] = _sourceBuffer[k + 0];
                        nextBuffer[i_step + 3] = _sourceBuffer[k + 1];

                    _index += _adjustedStepRate;

                if ((_index >= _sourceBuffer.Length - endOfBufferMargin))
                    _timeToStop = true;
                for (; i < (nextBuffer.Length/4); ++i, i_step += 4)
                    nextBuffer[i_step + 0] = 0;
                    nextBuffer[i_step + 1] = 0;
                    if (_channelCount == 2)
                        nextBuffer[i_step + 2] = 0;
                        nextBuffer[i_step + 3] = 0;

        void _dse_BufferNeeded(object sender, EventArgs e)

        private byte[] _sourceBuffer;

        public AdjustedSoundEffect(Stream source): this()
            byte[] header = new byte[44];
            source.Read(header, 0, 44);

            // I'm assuming you passed a proper wave file so I won't bother 
            // verifying  that  the  header  is properly formatted and will 
            // accept it on faith :-)

            _channelCount = header[22] + (header[23] << 8);
            _sampleRate = header[24] | (header[25] << 8) | (header[26] << 16) | (header[27] << 24);
            _bytesPerSample = header[34]/8;
            _byteCount = header[40] | (header[41] << 8) | (header[42] << 16) | (header[43] << 24);
            _sampleStep = _bytesPerSample*_channelCount;
            _sourceBuffer = new byte[_byteCount];
            source.Read(_sourceBuffer, 0, _sourceBuffer.Length);

            _baseStepRate = ((float)_sampleRate) / PlaybackSampleRate;

        /// <summary>
        /// </summary>
        /// <param name="pitchFactor">Factor by which pitch will be adjusted. 2 doubles the frequency,
        /// // 1 is normal speed, 0.5 halfs the frequency</param>
        public void Play(float pitchFactor)
            _timeToStop = false;

            _index = 0;
            lock (SyncRoot)
                _adjustedStepRate = _baseStepRate * pitchFactor;
                _index = 0;
                playbackBufferIndex = 0;
                IsPlaying = true;

        public void Stop()


Adding an E-Mail Account to the WP Emulator

For one reason or another you may find that you want to add a real e-mail account to the Windows Phone emulator. Unfortunately the emulator doesn’t directly expose a way for you to do this; the settings area on the phone doesn’t display the tile to access the e-mail settings. You can get to the settings application indirectly though. This path is convoluted, but it works.

You’ll need to make a simple application that does nothing more than show a phone call task. Once the task is displayed accept the phone call then select the option to add another caller. This takes you to the People Hub. Swipe through the People Hub to the &quotWhat’s New" and you will be prompted to add a Facebook or Twitter account. Select the option to do this (even though you are not really adding an account of that type) and when you asked what type of account you want to add you can select one of the e-mail account types.

Setting Custom Ringtones from Code [Mango:Beta 1]

Written against pre-release information

One of the new features coming with the next update to Windows Phone 7 is the ability to set custom ring tones. From within code you can make a ring tone available to a user (it’s up to the user to accept the ring tone, so user settings won’t ever be changed without user permission). I was looking at the new API for doing this, the SaveRingtonTask()

To use the API you first need to get the ringtone of interest into isolated storage. It can be either an MP3 file or a WMA file up to 30 seconds in length. If the file is a part of your application. Just set it’s build type to "Resource".

file settings

Getting the file from being packed in the application to isolated storage is a matter of reading from a resource stream and writing to isolated storage.

s =
    Application.GetResourceStream(new Uri("/MyApplicationName;component/1up.mp3",
    using (var f = IsolatedStorageFile.GetUserStoreForApplication().CreateFile("1up.mp3"))

        var buffer = new byte[2048];
        int bytesRead = 0;

            bytesRead = s.Stream.Read(buffer, 0, 1024);
            f.Write(buffer, 0, bytesRead);
        } while (bytesRead > 0);


Once the file is in isolated storage you must pass the URL to the SaveRingtoneTask(). URIs to isolated storage are preceded with "isostore:" (there is also an "appdata:" prefix, but we won’t be using it here). Give the ringtone a display name and call the show method to present the user with the option to save it. If you don’t set the

SaveRingtoneTask srt = new SaveRingtoneTask();
srt.DisplayName = "1up";
srt.IsoStore= new Uri("isostore:/1up.mp3", UriKind.Absolute);
srt.IsShareable = true;

Peer Communication on Windows Phone 7

Written against pre-release information

One of the new things that we get with Windows Phone 7 is socket support. While I expected to be able to open sockets to other machines with servers running on them one thing caught me by surprised; that you can also send communication from phone to phone using UDP. I’ve got to give credit to Ricky_T for pointint out the presence of this feature and posting a code sample. I wanted to try this out myself. So I made a version of the code sample that would run on both Windows Phone and on the desktop (Silverlight 4 in Out of Browser mode). I was pleasantly surprised to that I was able to open up peer communication between the desktop and phone without a problem. This capability provides a number of solutions for other problems that I’ve been considering, such as automatic discovery and configuration for communicating with services hosted on a user’s local network. 

Most of the code used in the desktop and phone version of this example are identical; I’ve shared some of the same files between projects. From the files that are not shared the counterparts in the phone and desktop version are still similar.  The core of the code is in a class called Peer. Let’s take a look at part of the body of that class. 


//Define the port and multicast address to be used for communication
private string _channelAddress = "";
private int _channelPort = 3007;

//The event to be raised when a message comes in
public event EventHandler<MessageReceivedEventArgs> MessageReceived; 

//the UDP channel over which communication will occur.
private UdpAnySourceMulticastClient _channel;

//Create tje cjamme;
public void Initialize()
    _channel = new UdpAnySourceMulticastClient(IPAddress.Parse(_channelAddress), _channelPort);

//Open the channel and start listening
public void Open()
    if (_channel == null)
    ClientState = ClientStatesEnum.Opening;

    _openResult = _channel.BeginJoinGroup((result) =>
                                                    ClientState = ClientStatesEnum.Opened;
                                                }, null);   


//The receive method is recursive. At the end of a call to receive it calls itself 
//so that the class can continue listening for incoming requests.
void Receive()
    byte[] _receiveBuffer = new byte[1024];

    _channel.BeginReceiveFromGroup(_receiveBuffer, 0, _receiveBuffer.Length, (r) =>
            IPEndPoint source;
            int size= _channel.EndReceiveFromGroup(r, out source);
            OnMessageReceived(_receiveBuffer, size,  source);                                                                                   
            catch (Exception )
    }, null);
public void Send(byte[] data)
        _channel.BeginSendToGroup(data, 0, data.Length, (r) => _channel.EndSendToGroup(r),null);

This class only sends and receives byte arrays. My only goal here was to see the code work so there are other considerations that I have decided to overlook for now. I made a client to use this code too. The client sends and receives plain text. Before sending a block of text it is necessary to convert the text to a byte array. The encoding classes in .Net will take care of this for me. When a message comes in I can also use an encoder to convert the byte array back to a string.

For this program I am adding the incoming message to a list along with the IP address from which it came

void _peer_MessageReceived(object sender, MessageReceivedEventArgs e)
    Action a = () =>
                        string message = System.Text.UTF8Encoding.Unicode.GetString(e.Data, 0, e.Size);
                        MessageList.Add(String.Format("{0}:{1}", e.Endpoint.Address.ToString(), message));
                        OnIncomingMessageReceived(message, e.Endpoint.Address.ToString());
    if (UIDispatcher == null)

public void SendMessage(string message)
    byte[] encodedMessage= UTF8Encoding.Unicode.GetBytes(message);

When the code is run on any combination of multiply phones or computers a message types on any one of the devices appears on all of them. Nice! Now to start making use of it.

John Conway’s Game of Life part 1 of N

The Game of Life is a refinement of an idea from John von Newman in the 1940’s. The refinement was done by John Conway and appeared in Scientific America in October 1970. I’ll skip over the details of why such a program is of interest. But the program produces some interesting patterns.

The typical version of the game is composed of a grid of cells where some number of cells are initially marked as having life. The grid of cells is evaluated and cells get marked as alive or dead based on a small set of rules based on it’s neighbors. Two cells are neighbors with each other if they touch diagonally or side-by-side.

  1. Any live cell with fewer than two live neighbours dies, as if caused by under-population.
  2. Any live cell with two or three live neighbours lives on to the next generation.
  3. Any live cell with more than three live neighbours dies, as if by overcrowding.
  4. Any dead cell with exactly three live neighbours becomes a live cell, as if by reproduction.

The above algorithm enough and the program is easy to implement. The challenge is more in creating a decent user interface for the program. I decided to make this program myself. The first step in making the program was to implement the algorithm. I wanted to make sure the algorithm worked so I created a simple XNA program that would allow me to see the algorithm work. It’s non-interactive so you can only see the program run but not impact the outcome.

Theres a small amount of data that needs to be tracked for each cell. I need to know if a cell is alive and whether or not it should be alive during the next cycle. The cell will also need to interact with other cells in the community. Some time in the future I plan to allow the cells to express something about the parent from which it came. Though I won’t be doing that for this first version.

public class Cell
     public CellCommunity  Community   { get; set; }
     public bool           IsAlive     { get; set; }
     public bool           WillSurvive { get; set; }
     public Gene           GeneList { get; set; }

The community of cells themselves will be saved in a two dimensional array. The cell community class has two methods that will do the work of calculating whether or not a cell should be alive the next cycle and another for applying the results of those calculations.

public void EvaluateNewGeneration()

    for (var cx = 0; cx < CellGrid.GetUpperBound(0); ++cx)
        for (var cy = 0; cy  MAX_NEIGHBOR_COUNT) || (neighborsneighborList.Length < MIN_NEIGHBOR_COUNT))
                    KillCell(cx, cy);
                    KeepCellAlive(cx, cy);
                if ((neighborsneighborList.Length ==3))
                    KeepCellAlive(cx, cy);

public void ApplySurvival()
    for (var cx = 0; cx < CellGrid.GetUpperBound(0); ++cx)
        for (var cy = 0; cy < CellGrid.GetUpperBound(1); ++cy)
            var cell = CellGrid[cx, cy];
            if (cell != null)
                cell.IsAlive = cell.WillSurvive;

I decided to make the UI in XNA. I have an idea on how to visualize a cell changing state and I can more easily implement it using a 3D API. Since the "world" of the Game of Life is in a grid I’m going to represent the state of a cell with a square that is either black (if the cell is not alive) or some other color (if the cell is alive). I’m drawing the squares by rendering vertices instead of writing sprites. This give me greater liberty in changing the color or shape of a cell. The following will draw one of the squares.

const int _squareWidth = 5;
const int _squareHeight = 5;
private const int _offsetX = -_squareWidth*30;
private const int _offsetY = -_squareHeight*18;

void DrawSquare(int x, int y, Color c)
    _vertices[0].Color = c;
    _vertices[1].Color = c;
    _vertices[2].Color = c;
    _vertices[3].Color = c;

    _vertices[0].Position.X = _offsetX + _squareWidth * x + _squareWidth;
    _vertices[0].Position.Y = _offsetY + _squareHeight * y;

    _vertices[1].Position.X = _offsetX + _squareWidth*x;
    _vertices[1].Position.Y = _offsetY + _squareHeight*y;

    _vertices[2].Position.X = _offsetX + _squareWidth * x + _squareWidth;
    _vertices[2].Position.Y = _offsetY + _squareHeight * y + _squareHeight;

    _vertices[3].Position.X = _offsetX + _squareWidth * x;
    _vertices[3].Position.Y = _offsetY + _squareHeight * y +_squareHeight;

    graphics.GraphicsDevice.DrawUserPrimitives(PrimitiveType.TriangleStrip, _vertices, 0, _vertices.Length-2);     

With the ability to draw the square completed it’s easy to iterate through the collection of cells and render them to the screen according to whether or not they are alive.

protected override void Draw(GameTime gameTime)

    var effect = new BasicEffect(GraphicsDevice);
    effect.World = _world;
    effect.Projection = _projection;
    effect.View = _view;
    effect.VertexColorEnabled = true;
    effect.TextureEnabled = false;
    effect.LightingEnabled = false;

    foreach(var effectPass in effect.CurrentTechnique.Passes)
        for (int cx = 0; cx < 60;++cx )
            for(int cy=0;cy<36;++cy)
                Color c = _community.IsAlive(cx, cy) ? Color.Red : Color.Black;

I manually populated the grid and let it run. I’m happy to say it seems to be working. Now onto designing and making the user interface.

Screen Shot

What’s Coming to Windows Phone in 2011?

With more that 13,000 applications in their Marketplace Microsoft came out on stage today to make some new announcements about what’s coming to Windows Phone 7. We’ll see a major upgrade on all Windows Phone devices by the end of the year and developers are getting access to a lot of new APIs enabling new application scenarios.

Here is a summary list of the new features.

  • Multitasking – in addition to faster application switching multitasking will allow applications to continue processing in the background.
  • Live Tile Functionality Enhancements
  • Sensor Library Enhancements – You’ll have enhanced access to the sensor library and
      Access to the camera and compass-! Reality augmentation is possible!
    • Sockets – This needs no explanation
    • Database
    • IE9 – with hardware acceleration
    • Silverlight+XNA – you can use Silverlight and XNA in the same application
    • Twitter in the People Hub
    • Background Transfers
    • Profile
    • Silverlight 4 Runtime

    Several new countries are being added to the Marketplace. This brings up the total count from 17 to 35. The new countries are listed below with *.

    • Australia
    • Austria
    • Belgium
    • Brazil*
    • Canada
    • Chile*
    • Columbia*
    • Czech Republic*
    • Denmark*
    • Finland*
    • France
    • Germany
    • Greece*
    • Hong Kong
    • Hungary*
    • India*
    • Ireland
    • Italy
    • Japan*
    • Mexico
    • Netherlands*
    • New Zealand
    • Norway*
    • Poland*
    • Portugal*
    • Russia*
    • Singapore
    • South Africa*
    • South Korea*
    • Spain
    • Sweden*
    • Switzerland
    • Taiwan*
    • UK
    • USA /