What Are Decibels?
The decibel (dB) is a ratio, not a fixed amount. +6 dB means roughly double the amplitude; +20 dB means ten times the amplitude. Our ears perceive loudness logarithmically, so equal dB steps sound like equal loudness steps, even when the raw amplitude changes are wildly different.
Ratios, Not Amounts
Decibels don't measure a fixed quantity of "loudness." They measure the ratio between two levels. The formula is simple: dB = 20 × log10(amplitude), where amplitude 1.0 is our reference point (0 dB).
Double the amplitude and you get +6.02 dB. Ten times the amplitude is +20 dB. Half the amplitude is −6 dB. This means going from 0.5 to 1.0 is exactly the same dB change as going from 1.0 to 2.0. Both are +6 dB, even though the linear distance is different.
Why Logarithmic?
Our ears don't respond linearly to amplitude. Doubling the amplitude doesn't sound "twice as loud." It sounds like one noticeable step louder. The dB scale compresses this huge range into manageable numbers that match our perception: equal dB steps sound like equal loudness steps.
This is why mixer faders are marked in dB, not linear amplitude. A fader move from −12 to −6 sounds the same as −6 to 0: each is a doubling of amplitude, each sounds like one "step" louder.
dB in Synthesis
Decibels appear everywhere in synthesis: master volume, filter gain, oscillator mix levels, envelope depth. When a synth says a filter boosts by 12 dB, it means the signal amplitude quadruples at that frequency. When an envelope's depth is −24 dB, it means the signal drops to 1/16th of its peak.
Try the demo below: drag the amplitude slider and watch how the linear bar, dB readout, and waveform all respond. Notice that the perceptual "halfway point" isn't at amplitude 1.0. It's somewhere around 0.1, where the dB scale reads −20.
Drag the amplitude slider and watch all three views update. Moving from 0.5 to 1.0 and from 1.0 to 2.0 look different on the linear bar but are both +6 dB, the same perceptual change.
Amplitude controls the gain node directly (0.0 to 2.0). The dB readout converts this using 20 × log10(amplitude). Each preset sets a specific amplitude. Notice how equal dB spacing (6 dB per step) means doubling or halving the amplitude each time.