Figure 1. Attack and decay.
Figure 2. Attack of a piano note.
Attack is the initial period of a typical envelope during which a sound's attribute (such as volume) increases from 0 (silence) to its maximum amount. The length of the attack determines how soft or harsh a sound is. For example, most drum or percussion sounds have a short amplitude attack time and thus have a sudden "harsh" start. A string sound usually has a long amplitude attack and thus has a "soft" start and eases in. See also decay; ADSR.
Attack time may refer to:
Example: attack of a piano note
The start of a note must be heard if it is to be recognized. The graph in Figure 2 shows that a piano note, for example, reaches its peak volume very soon after it has been struck [A]. It then begins to fall away with greater rapidity at first, before tailing away slowly for several seconds. This is what gives the instrument its attack. The same note produced on a gong takes a comparatively long time to build up and, although of the same pitch, sounds completely different. The same piano note played backwards on a tape recording [B] slowly increases in volume and then suddenly stops. Shorn of its start, the sound is totally unlike a piano and more like an organ.