Like Harmonic content, the envelope helps the listener distinguish one instrument or voice from the other. The envelope contains four distinct characteristics: attack, decay, sustain, and release.
The attack is the first point of a note or sounds envelope. It is identified as the area that rises from silence to its peak volume. Decay is the next area of the envelope that goes from the peak to a medium level of decline. Sustain identifies the portion of the envelope that is constant in the declining stage. The release identifies the last point in the envelope where the sound returns back to silence. A percussive instrument has a very quick attack, reaching the note instantly upon striking. With woodwinds, brass, and reed instruments, no matter how quickly the note is played, it will never reach the note as fast as striking a drum.
Other Periodic Waveform Types
Waveform defines the size and shape of a sound wave. Up to this point, a simple sine wave has been used to illustrate sound. Sound can come in different waveforms, other than a sine wave. Other common waveforms include triangle, square, and sawtooth waves. Each waveform has its own sound and characteristics and each may be used for different applications.A triangle wave looks like a triangle when viewed on an oscilloscope, a square wave appears as a square, and a sawtooth wave appears as a sawtooth.
A square wave is typically associated with digital audio. A square wave’s sound is often described as hollow and contains the fundamental note plus the odd harmonics. These harmonics gradually decrease in amplitude as we go higher in the frequency range.A triangle wave is similar to a square wave in that it also contains only the fundamental plus the odd harmonics. It is a kind of a cross between a sine wave and a square wave. One main difference is that the higher frequencies harmonics are even lower in amplitude than those of square waves. This results in a less harsh sound and is often used in synthesis.A sawtooth wave contains both the even and the odd harmonics of the fundamental. Its sound is harsh and clear. Sawtooth waveforms are best known for their use in synthesizers and are often used for bowed string sounds.