C# bridge DLL to speex (with example code)

I need a C# DLL (with source code) , to act as a "bridge" to access the speex dll. This dll should be capable of encoding and decoding raw pcm audio bytes delivered through its API. The implementation of a PCM to speex stream class and a speex to PCM stream class would be a plus. One example source code of encoding and decoding should be enough.