Procedural Audio in 3D

I'm generating audio procedurally by using the OnAudioFilterRead but the output or the spatial blend is 2D. If I change it to 3D in the AudioSource it just won’t sound.

Does somebody knows how can I set this to have 3D sound properties?

     void OnAudioFilterRead(float[] data, int channels)
     {
         // update increment in case frequency has changed
         increment = frequency * 2 * Math.PI / sampling_frequency;
         for (int i = 0; i < data.Length; i = i + channels)
         {
             phase = phase + increment;
             // this is where we copy audio data to make them “available” to Unity
             data[i] = (float)(gain*Math.Sin(phase));
             // if we have stereo, we copy the mono data to each channel
             if (channels == 2) data[i + 1] = data[i];
             if (phase > 2 * Math.PI) phase = 0;
         }
     }