A little more than a year ago, VATSIM announced their new audio codec, called ‘Audio for VATSIM’. It promises a realistic VHF and HF radio simulation, including optional realistic distortion and white noise, up to 80% reduction in latency and range simulation (signal strength now decreases with distance).
The update is being pushed to the servers right now. If you haven’t updated your client yet, you should do it now, as the new codec will come live today at 21:00 CET.
Not sure how to update? VATSIM has prepared a simple guide here.