The first cut will be using Jitsi as the engine, albeit with more appropriate UI, which gives you AEC (echo cancellation) from WebRTC and some level of AGC (normalisation). But we have plans to go far beyond that, and are very aware it’s hard work. However, pre-Matrix, the core team professionally built VoIP stacks, so we have some experience here (and our own WebRTC implementation should we need it :)