Problem with a record function in csharp

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C#

C#4.0

Hello

I have a record function which let me to record a vocal message and to save it in my pc. Then it gives us the possibility to hear the recorded message,the problem is that when I install an external sound card the function stops recording sound from my default sound card and it records it from the other audio card,so can you give me an idea to oblige the record function to use only the default sound card. This is the record code:

public partial class RecordingForm : Form
    {
        IWaveIn waveIn;
        WaveFileWriter writer;
        string outputFilename;
        public RecordingForm()
        {
            InitializeComponent();
            //LoadWasapiDevicesCombo();
        }
        private void LoadWasapiDevicesCombo()
        {
            MMDeviceEnumerator deviceEnum = new MMDeviceEnumerator();
            MMDeviceCollection deviceCol = deviceEnum.EnumerateAudioEndPoints(DataFlow.Capture, DeviceState.Active);
            Collection<MMDevice> devices = new Collection<MMDevice>();
            foreach (MMDevice device in deviceCol)
            {
                devices.Add(device);
            }
            this.comboDevices.DataSource = devices;
            this.comboDevices.DisplayMember = "FriendlyName";
        }
        private void buttonStartRecording_Click(object sender, EventArgs e)
        {
            if (waveIn == null)
            {
                if (outputFilename == null)
                {
                    buttonSelectOutputFile_Click(sender, e);
                }
                if (outputFilename == null)
                {
                    return;
                }
                waveIn = new WaveIn();
                waveIn.WaveFormat = new WaveFormat(8000, 1);
                writer = new WaveFileWriter(outputFilename, waveIn.WaveFormat);
                waveIn.DataAvailable += new EventHandler<WaveInEventArgs>(waveIn_DataAvailable);
                waveIn.RecordingStopped += new EventHandler(waveIn_RecordingStopped);
                waveIn.StartRecording();
                buttonStartRecording.Enabled = false;
            }
        }
        void waveIn_RecordingStopped(object sender, EventArgs e)
        {
            if (this.InvokeRequired)
            {
                this.BeginInvoke(new EventHandler(waveIn_RecordingStopped), sender, e);
            }
            else
            {
                waveIn.Dispose();
                waveIn = null;
                writer.Close();
                writer = null;
                buttonStartRecording.Enabled = true;
                progressBar1.Value = 0;
                if (checkBoxAutoPlay.Checked)
                {
                    Process.Start(outputFilename);
                }
            }
        }
        void waveIn_DataAvailable(object sender, WaveInEventArgs e)
        {
            if (this.InvokeRequired)
            {
                this.BeginInvoke(new EventHandler<WaveInEventArgs>(waveIn_DataAvailable), sender, e);
            }
            else
            {
                writer.WriteData(e.Buffer, 0, e.BytesRecorded);
                int secondsRecorded = (int)(writer.Length / writer.WaveFormat.AverageBytesPerSecond);
                if (secondsRecorded >= 30)
                {
                    StopRecording();
                }
                else
                {
                    progressBar1.Value = secondsRecorded;
                }
            }
        }
        void StopRecording()
        {
            Debug.WriteLine("StopRecording");
            waveIn.StopRecording();
        }
        private void buttonStopRecording_Click(object sender, EventArgs e)
        {
            if (waveIn != null)
            {
                StopRecording();
            }
        }
        private void buttonSelectOutputFile_Click(object sender, EventArgs e)
        {
            SaveFileDialog saveFileDialog = new SaveFileDialog();
            saveFileDialog.Title = "Select output file:";
            saveFileDialog.Filter = "WAV Files (*.wav)|*.wav";
            saveFileDialog.FileName = outputFilename;
            if (saveFileDialog.ShowDialog() == DialogResult.OK)
            {
                outputFilename = saveFileDialog.FileName;
            }
        }   
    }
}

Thank you in advance and good day