Introduction: Rapture3D and Ambisonics

Rapture3D is all about 3D sound. With the march of 3D film and television, immersive virtual reality and Really Good Games, it's about time for a real step forward in the quality of spatial audio.

You've probably been hearing how great commercial 5.1 or 7.1 surround sound systems are. So why would you care about something new? Well, 5.1 and 7.1 are not 3D formats (sounds don't move above and below) and it isn't always easy to convert mixes between the two formats. Or the others being discussed for the future.

In contrast, Blue Ripple Sound is building on an existing body of academic knowledge in the field of "Ambisonics". We've been working in this area for a while. (You can find out a bit more about us.) There's a lot of maths involved, but in our opinion, not only does this approach deal with the issues above, but typically it results in a much more accurate and immersive soundfield than other techniques.

Rapture3D OpenAL Game Engine

The Rapture3D OpenAL Game Engine is an "OpenAL driver". That's a piece of software that can be loaded into a computer game to look after sound placement. The game tells Rapture3D what sounds should be playing where and when, and Rapture3D gets on with the maths to make that happen. It feeds a theoretical Ambisonic "soundfield" representation to the Rapture3D Decoder (see below).

Rapture3D can be used easily with a few OpenAL PC games already, and more if you're prepared to modify your system. If you're a developer working on something that could make use of Rapture3D's superb 3D audio, we have some more information here.

Features include:

• 32bit floating point audio path.
• High quality sample rate conversion (used for various purposes including Doppler shift).
• High quality effects and filters.
• Directional sound sources.
• Support for multi-channel sound sources (including Ambisonic sound sources).
• No limit on the number of sources or effects except CPU power. Able to render hundreds of sound sources and multiple effects on relatively old hardware.
• Higher Order Ambisonic (HOA) bus running at up to fourth order.

The theoretical Ambisonic "soundfield" representation is then passed to the the Rapture3D Decoder.

Rapture3D Decoder

This component takes an Ambisonic feed and plays it back on the speakers available. Features include:

• Support for all the standard DirectSound Windows speaker layouts, including 5.1 and 7.1 and some special variants such as 3D7.1.
• Access to audio hardware via DirectSound.
• 3D sound over headphones. This uses psychoacoustic techniques based on head shape. Five different "HRTFs" are provided.
• Optional patent-pending tinting on multichannel layouts to add psychoacoustic spatial cues.
• HCTC crosstalk cancelled stereo options (also using psychoacoustic cues).
• Surround stereo encoders.

With the "user" version of the software, the decoder synchronises with your Windows settings. With the "advanced" version it doesn't, putting everything under the user's control. Other features in the advanced version are:

• Access to audio hardware via ASIO (this can allow sample synchronised access to large numbers of channels of extremely high quality, low latency audio hardware).
• Decoder generation for custom layouts. You enter where the various speakers have been located into the set up program and the generator will then generate a new decoder optimised for that arrangement. This includes support for irregular rigs (within reason!) and NFC to compensate for wavefront curvature.

Rapture3D Ambisonic Player

This is a self-contained player application that can play back Ambisonic soundfiles. It supports .amb files and .wav files containing "FuMa"-tagged Ambisonic audio and "traditional" B-Format. There's also a DirectShow filter that works with these files in some media players.

The player provides a real-time visualisation of the soundfield being played back and ships with both the "user" and "advanced" versions of Rapture3D.

For more information on Ambisonic playback, click here.