Performing onset detection in audio without the use of an FFT

1. What is onset detection?
2. What is onset in music?

What is onset detection?

Onset detection is concerned with finding the start of a musical note immediately preceding the attack. Onset detection in conjunction with pitch detection are utilized in various processes such as pitch-shifting, synthesis, adaptive filtering and envelope generation, to name a few.

What is onset in music?

Onset refers to the beginning of a musical note or other sound. It is related to (but different from) the concept of a transient: all musical notes have an onset, but do not necessarily include an initial transient.