[e-t172]

Originally Posted by mark0077

I'm wondering whats the consensus on the best way to downmix the likes of 5.1 to 2.0 without losing any of the LFE information. I want to send the full range of output to the speakers and decide from there how best to transfer the lower frequency content.

I don't know about the "consensus", but for me personally, I use the LAV Audio mixer with LFE set to 1.58 (=+4 dB, because ITU BS.775 LFE +10dB + two channels -6dB). That's the proper way to do it if you truly have a system that is capable of handling the full LFE output without overloading.

Originally Posted by mark0077

I have windows speaker configuration set to 2.0 and set that I have full range speakers (not that I think it even has any impact).

It doesn't. I have yet to find a scenario in which the "full range" setting in the Windows audio properties has any measurable effect.

Originally Posted by mark0077

I'm not sure which is best, to let windows mix whatever I throw at it, ie 5.1, down to 2.0, or use lav audios mixing to convert the 5.1 to 2.0.

I have measured the downmix coefficients that the Windows audio engine uses to downmix 5.1 to stereo. They are (for the left channel):

L = (L + -3dB*C + -10dB*LFE + -1dB*SL + -8dB*SR) * -10dB

These are weird coefficients that don't match the ITU BS.775 recommendation. I don't know why Microsoft decided to use these coefficients; maybe they're following different advice. As far as I know BS.775 is the standard to follow, which makes these coefficients wrong. This is the main reason why I use the LAV Audio mixer to downmix, not the Windows mixer.

Originally Posted by mark0077

I know a lot of people use wasapi to try to avoid the windows mixer as its so bad.

The Windows mixer is not "bad". Aside from the differences in downmixing coefficients that I've described above, you would be hard-pressed to find any perceivable difference in audio quality. Aside from very specific cases, most people who use WASAPI use it for dubious reasons (typically, an overparanoid obsession about getting "bit-perfect" output).

(The only case I know of where the Windows audio pipeline would degrade quality in perceivable ways is back in the days of Windows XP, where IIRC people had legitimate complains about the resampler not being good enough. The pipeline was completely revamped in Vista.)

Originally Posted by mark0077

Note: Whats throwing me off about bypassing lav audio decoder and just using mpc audio renderer, set to exclusive wasapi, is that the lfe channel in any surround sound test clips I have tried from say Dolby, still seems to be getting mixed into the 2.0.

I'm not sure what the problem is. If your sub is capable of handling it, then LFE should be included in the 2.0 downmix.