Crossfade between songs
- Input
- Dois arquivos sobrepostos por 3 segundos
- Expected output
- Equal-power, potência constante na transição
Default curve for DJ mixes and podcast mixdowns.
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what is equal-power fade audio
The Weber-Fechner law describes human perception of sound intensity as logarithmic: a linear reduction in amplitude does not translate into a linear drop in perceived volume. The equal-power fade compensates for this by using the sine function for fade in and cosine for fade out, which keeps the combined power of two complementary curves constant throughout the transition.
Default curve for DJ mixes and podcast mixdowns.
For very short fades, the difference between linear and equal-power is imperceptible.
The 3 dB difference in the middle explains the linear fade's volume "hole".
A linear fade reduces amplitude proportionally over time, simple, but can sound abrupt at the midpoint. Equal-power uses a sinusoidal curve that maintains a more constant perceived volume, ideal for professional mixdowns and crossfades.
In long fades, 5 seconds or more, the difference is clearly audible: equal-power sounds more uniform, while linear has a roughly 3 dB drop that is noticeable in the middle of the transition. In very short fades, under 1 second, the difference is minimal or imperceptible.
Because sin(0) = 0 and sin(π/2) = 1, so sine starts at silence and ends at full gain, the right behavior for an entry. Cosine does the opposite, cos(0) = 1 and cos(π/2) = 0, ending in silence, the right behavior for an exit. Together, the two functions add up to power 1 at any point in the transition.
Equal-power. Of the five available curves (linear, equal-power, logarithmic, exponential, and s-curve), it is the one least likely to surprise on a crossfade or a generic fade, because it avoids both the linear fade's volume hole and the abrupt perceptual cut a poorly chosen curve can cause.
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