Oh, I see what you mean. First of all, it’s important to understand that there’s two types of multichannel (more than one stereo pair) soundcards:
Some cards provide a separate virtual device for each stereo output. For example, imagine a four channel (two stereo output) card of that type. In the configuration, you will see entries like this:
My Soundcard (Output 1 and 2) - default
My Soundcard (Output 1 and 2) - front (1/2)
My Soundcard (Output 3 and 4) - default
My Soundcard (Output 3 and 4) - front (1/2)
If I remember correctly, the M-Audio Delta cards work like this.
From the perspective of the software, it appears that there’s two separate stereo sound cards in your system “My Soundcard (Output 1 and 2)” and “My Soundcard (Output 3 and 4)”, but it’s actually only one, with two stereo outputs. The advantage is that even old applications that cannot handle multichannel sound cards can access the outputs separately.
For this type of sound card, it doesn’t really matter whether you choose “default” or “1/2”, because both refers to the first (and only) channel pair of the particular virtual device.
Other sound cards provide a single audio device, with multiple channel pairs. This approach is used by most onboard or cheap 5.1 PCI or USB cards designed for home theater DVD playback. For example, for a 5.1 card, you see something like this in the audio devices list:
My Soundcard - default
My Soundcard - front (1/2)
My Soundcard - rear (3/4)
My Soundcard - center/sub (5/6)
So there’s only a single device here, but three stereo pairs. (For most cards, you need to set the type of speakers in the Windows Control Panel to “5.1” or similar to see all channel pairs. If it still doesn’t work, there’s an option named “force multichannel output” on the WDM Devices page in mAirListConfig.)
Technically, “default” means “use the first available channels” - for stereo files, that’s 1/2, so it doesn’t matter if you choose default or 1/2. (Mono files are mixed up to stereo, so they’re also being played on 1/2.) It’s even possible to play multichannel audio files (e.g. 5.1 Ogg Vorbis files) using the “default” setting on a 5.1 card.
With a card of the second type, you should always pick the particular channel pair entries (1/2, 3/4, etc.) to ensure correct routing. Don’t use the “default” entry unless you’re only going to use the first output anyway. Mixing the “default” entry with specific “3/4” etc. entries might screw up the audio output.
