A sound wave is a vibration travelling through air, or another medium, as a moving pattern of pressure changes, and our ears pick that pattern up as sound. Something vibrates, it pushes and pulls on the air around it, and that push and pull spreads outward as a wave. It is the physical thing behind every note, voice and noise you have ever heard.
This is true of any sound from any source, an instrument, a voice, a speaker or a browser synth. The physics is the same wherever you meet it, and none of it is tied to one product. The speed figure further down is rounded, since it shifts a little with temperature and conditions.
A sound wave is a vibration that travels through air, or another medium, as a moving pattern of pressure changes, and your ears read that pattern as sound. It starts with a vibrating source: a plucked string, a speaker cone, a pair of vocal cords, anything that moves back and forth quickly. As that surface pushes outward, it presses the nearby air molecules together into a brief high-pressure squeeze, called a compression. As it pulls back, it leaves a low-pressure gap behind it, called a rarefaction. Repeat that many times a second and you have a train of squeezes and gaps spreading out into the room.
The important part is what actually moves. The pressure pattern travels outward, but the air itself mostly stays put. Each molecule nudges the one next to it and then settles back close to where it began, a little like a shove passing down a packed crowd while each person barely shifts their feet. So what reaches your ear is the pressure pattern, not a stream of air blown across the room. When that pattern arrives, it pushes your eardrum in and out in the same rhythm, and that is the moment a pressure wave becomes something you hear.
It is easy to blur these together, so it helps to keep them apart. The sound wave is the physical thing: the real pressure changes moving through the air. The waveform is its shape drawn out, the same wave plotted as a line on a graph. The frequency is how fast the pattern repeats, and the amplitude is how big it is, how far the pressure swings from its resting point. One is the thing itself; the other three are ways of measuring or picturing it.
A sound wave travels as a longitudinal wave, which means the air moves back and forth along the same direction the wave itself is moving. The compressions and rarefactions march outward from the source, and each little patch of air simply shuffles forward and back along that same line as the pattern passes through it. This is different from ripples on a pond, where the surface bobs up and down across the direction the ripple travels. In a sound wave, the motion and the travel run along the same axis.
A sound wave also needs a medium to travel through, because it works by one molecule passing a push to the next. Air is the usual one, but sound travels through water and through solids too, often faster and further. Where there is nothing to carry the push there is no sound: in the vacuum of space, with no molecules to pass it along, a sound wave cannot travel at all. In ordinary air near room temperature it moves at roughly 343 metres per second, which is why you tend to see a distant event a moment before you hear it. That figure is a round one rather than a fixed constant, since the speed shifts with the medium and with conditions such as temperature.
Roughly 343 metres per second is quick by everyday standards but slow next to light, which is why you see lightning before you hear the thunder, and see a far-off hammer strike before the knock reaches you. The sound is not late; it is simply travelling at the speed of sound. Treat the number as a good working average for air rather than an exact value for every room and every day.
A sound wave has three main properties, and each one maps onto something you hear. Its frequency is how fast the pressure pattern repeats, and that is heard as pitch. Its amplitude is how big the wave is, how far the pressure swings, and that is heard as loudness. And the shape of the wave, its waveform, is heard as timbre, the character that lets you tell one instrument from another. Change one and you change one thing about the sound; the other two can stay exactly as they were.
| Property of the wave | What it is | What we hear |
|---|---|---|
| Frequency | How many times the pressure pattern repeats each second, measured in hertz. | Pitch: faster repeats sound higher, slower repeats sound lower. |
| Amplitude | How big the wave is, how far the pressure swings from its resting point. | Loudness: a bigger swing sounds louder, a smaller one quieter. |
| Waveform shape | The exact shape of one cycle of the pressure pattern. | Timbre: the character that tells a flute from a violin on the same note. |
These three are worth keeping separate because a sound can change one without touching the others. Play the same note louder and its frequency does not move; only the amplitude grows. Two instruments can hold the very same pitch at the very same volume and still sound nothing alike, and that difference is the shape of the wave. If you want to go deeper on any one of them, frequency and the waveform each have a guide of their own.
A sound wave becomes audio when a microphone turns it into an electrical signal, and that signal is then measured many times a second to become a digital one. A microphone has a thin diaphragm that the passing pressure wave pushes back and forth, and that tiny movement is converted into a changing electrical voltage which traces the very same pattern as the pressure. At this stage the sound is no longer in the air; it is a wave of voltage running down a wire, but its shape is unchanged.
To store it on a computer, that voltage is sampled, which means it is measured thousands of times a second and each reading is written down as a number. Line those numbers up and you have the digital signal, a list of values that follows the original wave closely enough for the ear not to notice the joins. A speaker runs the whole thing in reverse: the signal drives a cone back and forth, the cone pushes the air into fresh compressions and rarefactions, and a pressure wave you can actually hear is born again. The shape carries through every stage, and only the thing carrying it changes: air, then electricity, then numbers, then air once more.
What survives every step from a voice to a speaker is the waveform, the shape of the wave. A microphone, a cable, a file and a loudspeaker are just different ways of carrying that shape, and each stage aims to change it as little as possible. When people talk about a recording being clean or faithful, this is what they mean: the wave that comes out of the speaker matches the wave that went into the microphone.
All of this theory has a practical edge. Whatever you play, sing or program, it leaves your speakers as a sound wave, so the cleaner and better shaped that wave is, the more clearly it lands on whatever someone plays it back on.
Every sound you make is a wave in the end, and the ones that translate best on any system, laptop speakers, headphones or a club rig, tend to start out clean and well shaped rather than being rescued later. The Collection is our three instruments together, with three separate licence keys, and they are voiced to give you clear, well-shaped waves from the start. ARGISH is a self-playing chord synth, SILT is a tape-loop instrument, and REHEAT writes acid lines, and whatever you make with them is yours to release. Each one ships as AU, VST3, AAX and a standalone app on macOS, signed and notarized, and a VST3 on Windows.
You can hear one free in your browser first, no install and no account, then decide.
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