First of all, all of the hardware components we have ordered have arrived and Graham has constructed the current head unit (see his blog for lots of photos). Also (besides exams :-/) I have the audio feedback system implemented (or, at least, the first version).
Before I move on to discuss this, I will talk a little about 3D sound.
The idea is that, through the attenuation, panning and modification of a sounds frequency, sounds can be made to appear to be positioned in 3D space, even though they are merely generated by a pair of stereo headphones. Crude models of 3D sound use only volume and panning to simulate a sounds positional properties. This works for simple left/right localization of sound, but it is extremely difficult (if even possible) for a person to differentiate between sounds coming from in front or behind. Up and down are also exceptionally difficult (or even impossible) to simulate using only volume and panning. FMOD supports this model of 3D sound, but also has a crude software implementation of HRTF, which changes the sounds frequency when the sound is behind the listener, to dampen the sound. This significantly improves the quality of the 3D-ness of the sound.
As an introduction to 3D sound, a number of 3D soundscape audio clips can be found on youtube. Two that I liked are found below (you will need a pair of stereo headphones for the full effect). This demonstrates the goal, in regards to audio, which myself and Graham are hoping to achieve.
Virtual barber shop:
Various 3D sounds:
The HRTF is a powerful means of simulating sounds as they would be heard by humans, if they (the sounds) were positioned in 3D around the user. The basic idea is to alter the sounds frequencies to simulate the sound waves reflecting and refracting off and around the listeners head and into the ear.
The angle at which the sound enters the ear and the speed of hearing the reflected sounds causes a change in the frequency of the sounds actually heard. These changes are used by the brain to position the sound in 3D space.
As everyones heads and ears are different, the HRTF will never be able to simulate 3D sound exactly, but it can come close enough to generate convincing 3D audio (similar to the youtube videos above, though they use binaural recording, which produces vastly superior results, but doesn't work with dynamic sounds, like we require).
3D sound using HRTF is important for high quality sound localization, but simulating 3D sound through HRTF is computationally expensive and not feasible to do in software in a realtime system. Luckily, some mid- and high-end soundcards (Creative X-Fi, for example) support hardware HRTF, which should vastly improve the quality of our 3D sound.
Some resources on 3D sound:
- Localization of sound sources (Michigan State University)
- Audio and 3D sound links
- FMOD Website
- Blog Entry about 3D Sound, HRTF and Sound Cards
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