Amplitude is the size or strength of a sound wave, how far it moves the air back and forth, and it is what we mostly hear as loudness. A bigger amplitude means a louder sound and a smaller amplitude a quieter one. On a waveform it is the height, the size of the peaks above and below the centre line. It is one of the three things that describe any sound, sitting alongside how fast the wave repeats and the shape of the wave.
This is true of any sound in any tool, a synth, a plugin, a DAW or a browser instrument. Amplitude and loudness are related but not identical, because human hearing is not linear, which is why level is measured in decibels and loudness in units like LUFS rather than in raw amplitude. The figures here are rounded, since our ears and our meters do not all draw the lines in the same place.
Amplitude is the size or strength of a sound wave, a measure of how far it moves the air away from rest, and it is what we mostly hear as loudness. Sound travels as fast, tiny changes in air pressure. Amplitude is how big those changes are, how far the pressure swings above and below the resting level on each cycle. Push the air harder and the swing is larger; nudge it gently and the swing is smaller.
On a waveform display, amplitude is the height. It is the distance from the centre line, the flat line of silence, up to the top of a peak and down to the bottom of a trough. A tall waveform is a big amplitude and a loud sound; a short one is a small amplitude and a quiet sound; a flat line is zero amplitude and no sound at all. Turning a track up or down is, at heart, making that height larger or smaller.
Amplitude is not the same as pitch or character. Amplitude, or level, is how big the wave is, heard as loudness and put on a scale of decibels. Frequency is how fast the wave repeats, heard as pitch and measured in hertz, which our guide on frequency covers. The waveform shape is the form of each cycle, heard as character or timbre. A sound can change one without the others: turn a note up and it gets louder while its pitch stays exactly the same.
Not quite. Amplitude is the physical size of the wave, while loudness is how loud that size actually seems to a person, and the two do not line up in a straight line. A bigger amplitude does sound louder, so they move in the same direction, but doubling the amplitude does not make a sound seem twice as loud. Our ears respond to ratios between levels rather than to flat differences, so equal changes in raw amplitude do not feel like equal changes in loudness.
This is why raw amplitude is an awkward number to read directly, and why level is placed on the decibel scale instead. The decibel is logarithmic, which roughly matches the way hearing works, so it turns a huge range of amplitudes into small, readable numbers. The decibel is the scale we put amplitude on; it does not replace amplitude, it just makes it easier to reason about.
Perceived loudness goes a step further again. When people talk about how loud a finished track is, especially for streaming, they usually mean a measurement in LUFS, a unit that tries to model how loud something seems to a listener by weighting the signal across time and across frequency, rather than reading its raw size. So it is worth keeping three ideas apart: amplitude is the raw physical size of the wave, decibels are the scale we place that level on, and LUFS is an attempt to measure the loudness a person actually experiences.
A bigger amplitude is a louder sound, but the relationship is not a straight line, because hearing is not linear. That is the whole reason level is quoted in decibels and loudness in units like LUFS rather than in raw amplitude. When a number needs to reflect what a listener hears, it is almost never the plain amplitude value.
Amplitude is usually described in two ways, peak and average, and on a meter it is shown in decibels below the top of the scale rather than as a raw figure. The two readings answer different questions, and most meters show both because neither tells the whole story on its own.
Peak amplitude is the single highest point the wave reaches, the tallest peak in the signal. It matters for staying clean, since a peak that goes over the top of the digital range clips and distorts, so engineers watch the peak to keep a signal under that ceiling. On its own, though, a peak does not tell you how loud something feels, because a signal can have one brief, tall spike and otherwise be fairly quiet. Average amplitude, often measured as RMS (root mean square), sums up the size of the wave over a short window instead of catching a single instant, so it follows the sustained energy in a signal and lines up better with how loud it seems.
| Measure | What it captures | What it is good for |
|---|---|---|
| Peak | the single highest point the wave reaches | catching clipping and keeping a signal under the ceiling |
| RMS or average | the size of the wave averaged over a short window | a rough guide to how loud a part actually feels |
| Loudness (LUFS) | perceived loudness modelled over time and frequency | matching levels between tracks and preparing for streaming |
Because raw amplitude values are hard to read, meters put them on a decibel scale, where the top of the digital range is zero and everything else sits below it as a negative number. A peak that reads a few decibels below the top has a little room left before it would clip. So the number on the meter is still amplitude; it has simply been placed on a scale that is easier to work with, and split into a peak reading and an average one so you can see both the loudest instant and the general level at a glance.
Amplitude is the size of the wave, heard as loudness, while frequency is how fast the wave repeats, heard as pitch, and they are completely separate properties of a sound. On a waveform they even sit on different axes: amplitude is the vertical size, the height of the peaks, and frequency is how tightly the cycles are packed along the horizontal, how many of them fit into each second.
Because they are separate, you can change one without touching the other. Turn a note up and its amplitude grows while its frequency, its pitch, stays exactly the same. Play a higher note at the same level and the frequency changes while the amplitude does not. A third property, the shape of the waveform, decides the character or timbre, which is why two instruments playing the same note at the same loudness still sound like different instruments. In short, amplitude answers how loud, frequency answers which note, and the shape answers what it sounds like.
Picture a waveform on screen. Amplitude is the up and down, the height of the peaks, heard as loudness. Frequency is the left to right, how closely the cycles are spaced, heard as pitch. Making a sound louder stretches it taller without changing how tightly the cycles are packed, so the loudness moves while the note stays put.
Getting amplitude right is far easier when the sound arrives at a sensible level to begin with. You can rescue a signal that is too hot or too weak later, but it is less work, and cleaner, when it was healthy in the first place. Good level control starts before the meter, with sources that were not fighting you from the start.
The Collection is our three instruments together, ARGISH, SILT and REHEAT, with three separate licence keys. Getting levels right starts with sources that arrive at a sensible amplitude, and these instruments output at clean, healthy levels, so you are not fighting a signal that is too hot or too weak before you have even started. 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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