如何改变录制声音的音调？

Question

I am creating an app which record sound. I am able to record and save the sound but i have to change the pitch of the recorded sound through slider. How can I do that? I am playing the recorded sound through media element. Here is the function to save the temporary audio file:

    private void SaveTempAudio(MemoryStream buffer)
    {
        // Be defensive ... trust no one & nothing
        if (buffer == null)
            throw new ArgumentNullException("Attempting to save an empty sound buffer.");

        // Clean out the AudioPlayer's hold on our audioStream
         if (_audioStream != null)
        {
            AudioPlayer.Stop();
            AudioPlayer.Source = null;

            _audioStream.Dispose();
        }

        using (IsolatedStorageFile isoStore = IsolatedStorageFile.GetUserStoreForApplication()) 
        {

            if (isoStore.FileExists(_tempFileName))
                isoStore.DeleteFile(_tempFileName);

            _tempFileName = string.Format("{0}.wav", DateTime.Now.ToFileTime());

            var bytes = buffer.GetWavAsByteArray(_recorder.SampleRate);

            _audioStream = isoStore.CreateFile(_tempFileName);
            _audioStream.Write(bytes, 0, bytes.Length);

            AudioPlayer.SetSource(_audioStream);
        }
    }

    private void PlayAudioClick(object sender, RoutedEventArgs e)
    {
        AudioPlayer.Play();
    }

Answer 1

Unless you find a library with the capability built in, you will have to get access to the individual sound bytes, convert them to frames, and cursor through the frames at the rate corresponding to the desired pitch. For example, if you want to play back at 150% speed, you would use linear interpolation to cursor through the data and provide the new values. Example: four frames with the values 0, 0.2, 0.4, 0.6. Cursor through at 150% means you get the first (0) then calculate halfway between the second and third (0.3), then get the fourth (0.6), etc. Then you take that frame data and convert that back to the audio bytes.