• Properties of sound

• The harmonic spectrum and the formants
• The envelope
• Sine wave graphs
• The pitch as a hertz value
• The Doppler effect

The envelope

(a.k.a. spectral envelope, contour, wave envelope, etc.)

When the same individual tone is produced using a cello and a piano, recorded and edited so that the beginning and the end of the tone are removed, they will be found to resemble each other considerably. In both cases, the string vibrates in a similar manner but something essential is missing from the timbre. Attack is the very short period of time that elapses before the sound has formed its spectrum. How instruments are identified usually depends on attack, while the pitch is generally detected from the timbral part of the sound and the sense of space determined by the sound's cadence. These successive parts of the sound are collectively referred to as the envelope. The attack spectrum of many instruments is inharmonic (noise), and its amplitude it stronger than the stationary part of the envelope (timbre). Despite its very short duration (often less than 0.1 seconds), attack is a significant factor that influences our identification of the instrument. The sound of a guitar, for example, could sound like a bell without the guitar's distinctive attack.