I believe that 'Point B' would officially be called 'Zero-Crossing' in most musical software. And most musical software has a choice to "snap to Zero Crossing".
I've just noticed that Audacity and WaveLab both use the 'Z' key to do this.
It is the point where there is 'no sound' on the left or right channel and if done as Devo has explained you should have points of 'no sound' at the beginning and end of your sample.

I must have done well, I got a sound card and an optical cable for my last kidney