alt Hacker NewsOverwhelmingly, there's no such thing as a zero crossing. Your closest real world case is a point in time (between samples) where the previous sample is positive and next one is negative (or vice versa). However, by truncating the next sample to zero, you create distortion (and if the absolute value of the preceding sample is large, very significant distortion.
Zero crossings were an early myth in digital audio promulgated by people who didn't know enough.
Fades are always the best solution in terms of limiting distortion (though even then, they can fail in pathological situations).
There's definitely such thing as a zero crossing, it's where sign(x[n-1]) != sign(x[n]) (or rather, there's "no such thing as a zero crossing" in the same way there's no such thing as a peak). Picking a suitable `n` as a start/end point for sample editing is a judgement call, because what you're trying to minimize is the difference between two samples since it's conceptually a unit impulse in the sequence.
I don't think people who talk about zero crossings were totally misguided. It's a legitimate technique for picking start/end points of your samples and tracks. Even as a first step before BLEP or fades.