Loudness and decibels
Loudness is the one thing every musician controls without thinking. To design sounds, you need it in numbers: decibels, and the strange way the ear hears different frequencies.
- Compare levels in decibels
- Explain why the ear hears some frequencies louder than others
- Hear how your touch changes the loudness
01Amplitude: how big the vibration is
Frequency is how fast a sound vibrates. Amplitude is how far it swings. A bigger swing pushes the air harder, and you hear it as louder.
But the ear doesn’t hear amplitude in a straight line. Doubling the amplitude does not sound twice as loud; it sounds “a bit louder”. Our hearing works in ratios, just as it does for pitch, so sound engineers measure level in decibels (dB), a scale of ratios:
| Change | Amplitude | You hear |
|---|---|---|
| +6 dB | × 2 | Clearly louder |
| −6 dB | × ½ | Clearly softer |
| −10 dB | × 0.32 | About half as loud |
| −20 dB | × 1/10 | Quiet |
| −40 dB | × 1/100 | Very quiet |
| 1 dB | × 1.12 | The smallest change most people notice |
Decibels: each step a fixed ratio
Decibels describe a ratio between two levels, so a dB number always needs a reference: louder than what? In KiMiA’s screens, 0 dB is usually the loudest a signal can be before it distorts, and every level below it is negative.
02The ear hears some frequencies louder
Here is something that surprises most musicians. Five sine waves, all with exactly the same amplitude, do not sound equally loud:
Five tones at the same level, as loud as the ear finds them
The ear is most sensitive in the middle and upper middle, roughly 1 to 5 kHz, which is where speech and the “presence” of instruments live. Low frequencies need much more energy to sound as loud. This sensitivity also changes with level: at quiet levels the ear loses the bass faster still. That is why music played softly can sound thin, and why a bass that sounds full in the studio can vanish on small speakers.
KiMiA uses this ear-weighted measure, called LUFS, to set the level of every sound it ships, including this course’s patches: each one sits at the same loudness, so switching sounds on stage never makes the level jump. The course patches you import are calibrated the same way.
03Your touch is loudness
On a piano, how hard you strike a key sets how loud the note is. A MIDI keyboard measures the speed of each key and sends it as velocity, a number from 1 to 127. KiMiA turns velocity into loudness with Edit›Amplitude envelope›Velocity → level:
How hard you play becomes how loud it is
The span between your softest and your hardest notes is your dynamic range. A dynamic range of about 20 dB between pp and ff feels like a piano. Turn Velocity → level down and every note plays at almost the same level (right for an organ); turn it up past 100% and your touch becomes more dramatic.
Loudness is only half of how a real instrument responds to touch: it also gets brighter. You will meet the other half, Velocity → brightness, in Module 5. Together they make a synth feel played rather than triggered.
04Headroom: leaving room at the top
Every digital system has a ceiling: a level above which the signal can’t go. Push past it and the tops of the waves are cut off, which sounds harsh and crackly. The space between your loudest moment and that ceiling is called headroom.
Notes add up: one note may be quiet, but a ten-note chord with the sustain pedal down can be ten times louder. KiMiA protects you twice. Its sounds are calibrated with room to spare, and its output ends in a limiter that turns the level down for a moment only when a peak would pass full scale, without bending the wave. (It sits at the end of the Sound path on Play, where it can be switched off.) Still, a good habit on stage is to set your sounds so the loudest passage you play reaches the top of the meter only rarely, and to use your mixer, not the synth, to make the whole band louder.
05Try it
- Hear 6 dB. Load 01 · Pure Sine. On the Play screen, move layer A’s volume slider from the top to exactly halfway while you hold a note. That is 6 dB.
- Test your speakers. Play C1 and C6 on the sine at the same velocity, on your laptop speakers and then on headphones. Which one disappears first?
- Measure your touch. Play a scale from your softest to your hardest touch. Then try Velocity → level at 50% and at 150%, and find the setting that feels most natural for your keyboard.
- Find the ceiling. Play a big chord with the sustain pedal down and watch KiMiA’s output meter. How many notes does it take to come close to the top?