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A sound is air being pushed. How fast you push decides the pitch; how hard you push decides the loudness; the shape of the push decides the timbre. Every sensation music can describe comes back to these three things.
How vibration becomes sound
An object vibrates, air is squeezed and released again and again, and that ripple reaches the eardrum, where it is heard as sound. The number of back-and-forth cycles per second is the frequency, measured in hertz. Human hearing spans roughly 20 Hz to 20 kHz, with the upper limit falling as we age.
Being audible is not the same as being usable as musical material. A musical tone must also satisfy three conditions: its pitch can be identified, held, and repeated. A scrap of sheet metal struck once is perfectly audible, but it never sounds the same twice — so it cannot be notated, rehearsed, or played in tune with anyone else.
Tones and noise
| Musical tone | Noise | |
|---|---|---|
| Vibration | Regular, periodic | Irregular, aperiodic |
| Perception | A definite pitch | Pitch is blurred; only timbre and loudness remain |
| Typical sources | Strings, pipes, reeds, the voice | Drums, cymbals, shakers, clapping |
"Noise" here is not a value judgement. An entire family of instruments is built on it, and the blurred pitch of a drum is exactly why it works as a timekeeper: an instrument with a strong, definite pitch would smear the melody instead.
A third category sits in between. Wood blocks, triangles and gongs have a pitch of sorts, but not a stable one, so notation for them usually records rhythm and leaves pitch out.
Diagram: two kinds of vibration
The four properties of a tone
| Property | Determined by | How we describe it |
|---|---|---|
| Pitch | Frequency | High / low |
| Duration | How long it lasts | Long / short |
| Loudness | Amplitude of vibration | Strong / weak |
| Timbre | Harmonic content and attack envelope | Bright / dark, thick / thin |
These four are independent. The same pitch can be struck gently or hammered; it can be held for bars or clipped short. Ear training feels hard precisely because in real playing all four move at once. Notation and solfège exist to separate the variables: staff position tracks pitch, note shape tracks duration, dynamic marks track loudness, and instrument and playing-technique labels track timbre.
Listen: a row of musical tones
The five tones below are separate, sharply bounded, and each one can be reproduced exactly. That is what makes them tones rather than mere sounds.
Common misconceptions
- "Louder means higher." No. Loudness comes from amplitude, pitch from frequency; they do not interact. Turn the volume up and the pitch does not move by a single hertz.
- "Noise means an ugly sound." It is a classification of vibration, not an aesthetic verdict. A snare drum plays noise for an entire movement.
- "Bass sounds like it is just louder." Bass means low frequency, which has nothing to do with loudness. Low instruments need a larger amplitude to be heard clearly — a different matter entirely.
- "If it has a pitch, it can be notated." Notation also demands that the pitch be stable enough to repeat, which is why gongs and wood blocks usually get rhythm only.
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Listen in the library
All tracks from midicn-lib — inline badge is the license tier (C1 commercial / C2 non-commercial / C3 study only).
Sources
- 声音由振动产生、人耳可听频率范围、乐音与噪音的区分，属声学与音乐声学通则
- 音的四项属性（音高 / 音长 / 力度 / 音色）为通行表述，本文行文为原创
Used for fact-checking only; all prose is original.