Function bs1770::reduce_stereo

pub fn reduce_stereo(
    left: Windows100ms<&[Power]>, 
    right: Windows100ms<&[Power]>
) -> Windows100ms<Vec<Power>>

Combine power for multiple channels by taking a weighted sum.

Note that BS.1770-4 defines power for a multi-channel signal as a weighted sum over channels which is not normalized. This means that a stereo signal is inherently louder than a mono signal. For a mono signal played back on stereo speakers, you should therefore still apply reduce_stereo, passing in the same signal for both channels.