Mixing 2 Audio Mono in 1 Stereo

Hi all

I'm trying to mix 2 audios mono in one audio stereo.
I want to develope a DirectShow filter to do the mixing cause I have 2 PCM MONO audio streams (the inputs of my filter) and I want 1 PCM Stereo (The Output)

Do anyone know an existing filter that do this?
If not, I would like the way to develope this filter.

Thanks to all people