I've been looking into XAudio2 and I found on my Creative Soundblaster X-Fi card on Windows XP, XAudio2 reports 6 channels on the master voice, despite my system being set to 7.1. Is this a driver limitation on Windows XP or XAudio2?

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Pete Goodwin

XAudio2 goes through a set of heuristics to figure out the "optimal" output format for a given audio device.  On Xbox it is always 48Khz float 5.1, and on Vista it's a fixed format determined by the user in the audio control panel, but on XP we start from our preferred format (44Khz float 5.1) and work backwards from there until we find something supported by the driver.  It sounds like in this case the X-Fi is claiming to support 5.1 natively (i.e. it lets us create a 5.1 H/W sound buffer to render to), so we go no further.  However, you should be able to use 7.1 by asking for it explicitly when you create the mastering voice.

Does that make sense?
Dugan Porter (XAudio2 dev)

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Dugan Porter [MS]
Game Audio Team

I found out today that I can ask for 8 voices, and the XAudio2 GetDeviceDetails reports 6, yet when I use SetOutputMatrix on the 8 channels, it works just fine.

Seems like the X-Fi is misreporting how many channels it has. I upgraded the drivers to "web update 5", I believe the latest, and now GetDeviceDetails reports 8 channels, and works as before.

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Pete Goodwin