Where a crash belongs
A crash cymbal marks a change: the first beat of a chorus, the drop after a build, the end of a fill. In most arrangements it plays once every eight or sixteen bars, so a single good sample goes a long way. Layer it with the kick on the downbeat so the two read as one hit.
Acoustic crashes carry a lot of low-mid “gong” alongside the shimmer. Cutting below 200 to 400 Hz keeps them from clouding the bass, and a gentle dip around 3 to 5 kHz tames harshness without losing air.
Choosing between them
Drum machine crashes, such as the 909’s, are short and noisy and sit well in dance music. Recorded crashes from free libraries have more natural decay and stereo width, which suits live-sounding productions and film cues. If a crash is too long, fade the tail rather than cutting it, or the end will click.