The typed messages in v1.5 are a good improvement, but certain situations demand more immediacy. I plan on adding voice communications, both to teammates and to everybody. Only one player can broadcast to everybody at a time and only one player per team can send to the team. I'd like to add a few more special effects to the audio. Right now it features simple stereo panning, Doppler effects, propagation delay, and attenuation with distance.
Ambient sounds are just background noises like music, crashing waves, a howling wind, etc.
I've no idea what kind of ambient sounds I'll have. An HRTF is a head related transfer function. It's a filter that simulates a human head. Right now I use a simple cosine based stereo panning function. I hope to replace this with a function that more accurately attenuates sounds depending of the source's direction.