The transfer function of a first-order digital all-pass filter takes the form: [ A(z) = \fraca + z^-11 + a z^-1, \quad |a| < 1 ]
for (int i = 0; i < samples; i++) x0 = input[i]; y0 = -c * x0 + (d - d c) * x1 + x2 - (d - d c) * y1 + c * y2;
By cascading multiple stages of these filters, AllPassPhase can "rotate" the phase of a signal, which is essential for creating phasers or aligning complex layers. Key Applications in Audio Production
Instead of aggressively EQing both instruments—which can thin out the mix—inserting an allpass filter on the bass track allows you to shift its low-end phase relative to the kick. This allows both instruments to occupy the same frequencies simultaneously while locking together perfectly in time, creating a massive, cohesive low end. Creative Audio Effects Born from Allpass Phase allpassphase
It introduces frequency-dependent time delays (phase shifts).
: It is frequently cited as a free, lightweight alternative to commercial plugins like Kilohearts Disperser Technical Details AllPassPhase - enummusic - Gumroad
An is a signal processing network that passes all frequency components with equal gain (unity gain) but changes the phase relationship between them [1, 2]. Mathematically, the frequency response The transfer function of a first-order digital all-pass
In live sound or high-end home theaters, sound travels from different drivers (woofers and tweeters). Because these drivers are physically located in different spots, their waves can reach your ear at slightly different times, causing "phase cancellation" where certain frequencies disappear. Engineers use all-pass filters to "bend" the phase of one driver to match the other, ensuring they add together perfectly. 2. The Foundation of Phasers and Flangers
): Experiences a shift of exactly -90 degrees (for a 1st-order filter) or -180 degrees (for a 2nd-order filter).
: By blending the processed wet signal at 50% with your clean dry track, the phase cancellations will instantly create a notch-filtering phaser effect. Creative Audio Effects Born from Allpass Phase It
Since "AllPassPhase" is specifically a software plugin created by , there isn't a single formal academic "white paper" written just for it. However, its core functionality is based on classic digital signal processing (DSP) principles. 📄 Relevant Research & Documentation
The all-pass filter also serves as a fundamental building block for synthesizing other filter types. A band-reject (notch) filter can be obtained by adding the output of an all-pass to the input signal and multiplying by (1/2). Conversely, a band-pass filter results from subtracting the all-pass output from the input. By varying a gain factor that multiplies the all-pass output from (-1) to (+1), one can smoothly transition from band-pass to band-reject behavior—a powerful technique used in audio phaser effects.
Second-order filters provide more complex, resonant phase shifts, often used in phaser effects to create sharp phase cancellations when summed with the original signal. 3. Applications of AllpassPhase in Audio and Engineering