"Amber" is a new decoder method that's available in Rapture3D on headphones and speakers in Rapture3D 2.4.11. This uses the free IRCAM AKG "Listen" HRTF data set (like "Orange"), but is processed with new and improved algorithms.
This works best on headphones - you'll need to put your computer into "Headphone" mode through Control Panel, or select "Headphone Stereo" or "Headphone Stereo (Compat.)" in the Rapture3D Speaker Layout program. Then on the "Decoder" tab, select "HRTF (Amber)" if it isn't selected already.
This way of listening to sound relies on HRTF processing - depending on the direction from which sounds are coming, we filter the sound differently to take into account how sound would curve around your head and ears in the real world. As heads are quite varied, HRTFs are a bit of a "black art", and different HRTFs work better for different people. Which is why we provide a range of different HRTFs to try - find one that's okay, and you'll probably find you get more used to it too. If you can find a good match, HRTFs allow Rapture3D to put sounds to the sides, behind, above and below, using just your headphones - which is particularly good when someone is creeping up on you in a game. If you're interested in this sort of thing, have a really careful listen - Rapture3D has the smoothest and cleanest HRTF behaviour that we've heard.
The IRCAM AKG "Listen" HRTF data contains measured HRTFs from about 50 different people - this must have taken a lot of effort and we're very grateful to the good folk of IRCAM for doing the work and making the results available to the world! What we've done is analyse this data and come up with an 'average' HRTF that is a sensible compromise, using some new work. As it's an average, it wouldn't be perfect for any of the people actually measured, but hopefully not awful for any of them either! It's certainly much better than conventional "panning" techniques.
As well as headphones, we've also used Amber in other decoders. In particular, the HCTC decoders can use it for 'cross-talk cancelled stereo' with stereo speakers. This technique is extremely sensitive to where you're sitting, but if you're in just the right place, and your speakers are separated by 50 degrees, you may be able to hear sounds all around, not just between the speakers. To try this, you need to be using a "Stereo" layout and the "HCTC (Amber)" decoder. We don't select this by default because of the sensitivity to position, but it might work for you!
The HRTF and HCTC decoders use a little more CPU than the "Panner" decoders. Try them and see if you can hear the difference!