Properties of sound

The pressure fluctuation that makes the sound can be periodical or non-periodical. In the first case the fundamental frequency determines the pitch (about 16-20000 Hz for a human ear). Non-periodical sound is called noise.
In music acoustics sounds can be classified in the following ways:

Harmonic sounds whose overtones are multiples of the fundamental frequency
Non-harmonic sounds whose overtones are NOT multiples of the fundamental frequency
Noise that contains sound with a wide frequency range

Traditionally the sounds called “tones” or “notes” belong to categories 1 and 2: wind instruments to 1, string instruments very close to 1 and most percussion instruments to 2. Real instruments always contain some sound from category 3 as well, but mostly the players try to minimize that (for example wind instruments´ sizzling or hissing sounds). In addition to that noise the relationships between the partials (overtones) determine the characteristic tone colour of a musical instrument

The distribution of the partials and noise relationship is best described by the sound spectrum, which is like a snapshot of sound at a certain moment. For example, a well controlled musical instrument’s sound spectrum shows very small changes with time. Intonation changes, noise and other instability means continuous and remarkable changes in the sound spectrum.

Fundamental properties of notes

In music theory the fundamental properties of notes are: the pitch, the volume, the duration, the attack and the timbre. This site focuses on the first two, which are roughly the same as frequency and loudness in terms of acoustics.

Graphs of different sound categories in time-amplitude coordinates