Allpassphase -

When you hear a lush, smooth reverb tail that doesn't obscure the original dry signal, you are hearing cascaded allpassphase networks. They randomize the phase of the reflections, making the reverb dense and smooth rather than bouncy and distinct.

Unlike standard high-pass, low-pass, or parametric EQ filters, an all-pass filter has a . It passes all frequencies with unity gain, meaning it does not alter the volume, boost the bass, or cut the treble of an incoming signal.

1st-order digital all-pass with (a = 0.5):

Instead, it manipulates the , introducing a frequency-dependent time delay. allpassphase

In the discrete-time (digital) domain, for a causal and stable all-pass filter:

: Set the center point where the phase shift will be most concentrated.

The most common consumer application of an all-pass phase shift is the used by guitarists and electronic musicians. A phaser splits an audio signal into two paths. One path remains untouched (dry signal). When you hear a lush, smooth reverb tail

If you mix a dry (original) signal with a phase-shifted version of the same signal (e.g., using an all-pass filter on a parallel bus), the resulting interference creates notches and peaks in the frequency spectrum. This is . It sounds hollow, boxy, or metallic. When using allpassphase on parallel channels, always check the polarity and the resulting frequency response.

In a standard low-pass filter, phase shift is a side effect of cutting highs. In an all-pass filter, phase shift is the only effect. As frequency increases, the phase shift progresses. For a first-order all-pass, the phase goes from 0° at DC (0 Hz) to -180° at Nyquist (half the sample rate). The fastest change in phase (peak group delay) occurs right at the filter’s cutoff frequency.

That "whooshing" psychedelic sound from 70s rock? That’s all-pass phase at work. A effect works by placing several all-pass filters in a row. By modulating the frequency where the phase shift occurs, the filter creates "notches" when mixed with the original signal. Because the phase is constantly moving, the notches sweep through the spectrum, creating that iconic sweeping sound. 3. Dispersion and Reverb Design It passes all frequencies with unity gain, meaning

refers to a specialized category of audio processing tools and plugins—most notably the free VST plugin AllPassPhase by enummusic

1. Multi-Microphone Alignment (Drums and Acoustic Instruments)

This precise symmetry ensures that the product of the magnitudes is always 1, confirming the flat magnitude response while still generating a frequency-dependent phase shift.