Hi,

I've been wondering about the technology used for so-called virtual surround circuits that seem to be in all the new stereo TVs. Does anyone know where I can find technical information or design diagrams, etc. online? I'm looking for such information as what part phase shifting filters play, what about impulse responses, HRTF, etc. Anyone with some ideas?

Maes

Hey.. they are all classified informations.. Corporate top secrets..

I'm not talking about individual company designs but rather scientific papers, etc. I've found lots of interesting references to this kind of stuff for real surround sound, expanded stereo, etc., but nothing concerning the technology used to take the sounds from a 2-channel TV stereo signal appear to come from behind.

An added thought came to mind so I thought I'd throw this in too. What about DirectSound3D. I'm not a programmer but I'm wondering about the basic concepts behind this. Is a card with a DSP required, or can it be emulated in software? Can directionality be introduced by phase shift? I've Googled DirectSound3D but the results so far haven't provide any conclusive answers.

If you're interested in directional audio APIs, OpenAL (the aural equivalent of OpenGL) has a free specification that might help.

Thanks for the reply. OpenAL looks interesting but I'm afraid it's a little too programming-centric for what I need. I'm looking more for conceptual or theoretical information related to spacialization. For example, if an airplane flies overhead, what auditory information tells the brain that the sound source is overhead? Obviously for moving objects, Doppler plays a part. But what for stationary sound sources? Is it phase, frequency, or something else? Are there any formulas available around the internet that don't require a Doctorate in Engineering to understand?

Then there's the challenge of placing virtual sound sources in places where no speakers exist. Based on some info I found after reading a thread on Doom9, I implemented some calculations in a program called Plogue Bidule (amazing software. check it out at www.plogue.com). I'm able to place sounds horizontally with sometimes uncanny accuracy (in other words a lot more than just a 50-50 phantom speaker between two stereo speakers). This is obviously a function of frequency and phase relationships. Now I'm wondering if the same can be done to position virtual sound sources vertically. I know that dedicated DSPs combined with EAX, DirectSound 3D, etc., are able to simulate vertical virtual sound sources, but I'm wondering if this can also be done through a series of calculations in software. The first step is to find some calculations and theoretical descriptions and try them out. So that's why I've started this thread.

Maes