Before we can understand "allpassphase," we must understand its parent: the All-Pass Filter.
An all-pass filter is a signal processing block with a unique, almost paradoxical property: It passes all frequencies with equal gain (0 dB). It does not boost or cut any part of the frequency spectrum. If you run white noise through an all-pass filter, the resulting frequency spectrum looks identical.
So, if it doesn't change the volume of any frequency, what does it do? It changes the phase relationship between frequencies. allpassphase
The term "allpassphase" essentially refers to the specific phase-shifting characteristics of these filters. By delaying certain frequencies relative to others (while keeping amplitude flat), an all-pass filter creates a measurable shift in the waveform’s time domain. This is why all-pass filters are also known as "phase equalizers" or "delay networks."
AllpassPhase is a digital audio processing technique/utility that applies an all-pass filter to modify the phase response of a signal without changing its amplitude (magnitude) spectrum. It’s used to correct phase alignment, create phase-based effects, or shape timing without altering perceived loudness or timbre. Before we can understand "allpassphase," we must understand
If you open your standard EQ plugin, what do you see? Usually, you see tools designed to change the volume of specific frequencies. You boost the highs to add air, cut the lows to remove mud, or scoop the mids for a rock tone.
But hidden in the "Special" or "Utility" menu of many advanced plugins lies a tool that defies this logic: the Allpass Filter. Second-order all-pass: H(z) = (b0 + b1 z^-1
Unlike a low-pass or high-pass filter, an Allpass filter does not cut or boost any frequencies. If you looked at its frequency response curve on a graph, it would be a flat line.
So, if it doesn't change the volume, what does it do? It messes with time. And in audio, messing with time changes everything.