How do I properly remove Acoustic Echo Cancellation using Speex?

Question

UPDATED: Overall code that I use

For this, you really have to look at Mark Heath article here: how to play and record at the sametime. With that, you can really directly understood the problem right? Which is, the played sound from mic, will be recorded back to mic .. in a loop. Hence, echo effect.

I start the record and play action within a btnRecord event:

private void btnRecord_Click(object sender, EventArgs e)
        {

            // set up the recorder
            btnRecord.Enabled = false;
            btnStop.Enabled = true;
            

            recorder = new WaveIn();
            recorder.DataAvailable += RecorderOnDataAvailable;

            // set up our signal chain
            bufferedWaveProvider = new BufferedWaveProvider(recorder.WaveFormat);
            savingWaveProvider = new SavingWaveProvider(bufferedWaveProvider, "tempx.wav");

            // set up playback
            player = new WaveOut();
            player.Volume = 1;
            player.Init(savingWaveProvider);

            // begin playback & record
            player.Play();
            recorder.StartRecording();

            
        }

And here is the code that get called when recoreded data available:

 private void RecorderOnDataAvailable(object sender, WaveInEventArgs waveInEventArgs)
        {
            //incoming data, process it
            //TODO: AEC should be done here
            IntPtr unmanagedPointer = Marshal.AllocHGlobal(waveInEventArgs.Buffer.Length);
            Marshal.Copy(waveInEventArgs.Buffer, 0, unmanagedPointer, waveInEventArgs.Buffer.Length);
            speex_preprocess_run(speex_state, unmanagedPointer);
            
            byte[] b = new byte[waveInEventArgs.Buffer.Length];
            Marshal.Copy(unmanagedPointer, b, 0, waveInEventArgs.Buffer.Length);

            // play it back
            bufferedWaveProvider.AddSamples(b, 0, waveInEventArgs.BytesRecorded);
        }

In the last line you can see that I put the resultant buffer from speex processing to be played again in the bufferedWaveProvider. Unfortunately, it is still the same: still the same echo effect.