[PD] Crossfade model

Hello,

Basically, I'm having a little internal argument with myself about the correct definition of a crossfade is.  I have two ideas of a crossfade, but which is right?

A) A slider that goes from -1..1. When the slider is at 0 both signals are at 1 (full volume). As you stray from zero in either direction, the corresponding input's (left - less than zero, or right - greater than zero) volume is reduced and the other input's volume stays at a maximum of 1.

or

B) You have a slider that goes from 0..1. The output is equal to Input1 * slider + Input2 * (1-slider)

This may sound confusing in writing, as I've written it quickly, but the corresponding diagram might help: http://defaced.net/buck/misc/xfade.jpg

Hopefully someone will know which is correct. Thanks for any help you can contribute.

-Jordan