This video is long... But the second half is very much optional expansion and deep dive into some theory of allpass filters.
The first few examples are much quicker, more practical examples of dåpf patched.

Please also check out an amazing series of patch examples from the one and only DivKid:
   • Wow! I didn't know All Pass Filters c...  

Thanks for watching :)
~Jason


Introducing dåpf, the first dedicated effects processor in the Instruō product line. The Instruō dåpf is a set of two analogue allpass filters.

You might be asking yourself, “What is the point of a filter that passes everything?” Allpass filters don’t actually attenuate frequency amplitudes directly, but rather alter the phase relationship of frequencies across the spectrum. Allpass filter stages appear in the vast majority of voltagecontrolled filter topologies as well as serving as a core building block within DSP.

The normalled I/O of dåpf allows for cascaded or independent use of the two allpass filter circuits, offering everything from classic phaseshifting to psychoacoustic stereo enhancement and synthetic Doppler effect.

• Two parallel allpass filters
• Independent attenuverters for voltage control
• 1Pole/2Pole configuration for left channel
• Cascaded normalisation
• Global 1 volt per octave tracking

00:00:00 Instruōduction
00:03:24 Overview | Stereo Enhancement
00:04:19 Stereo Enhancement Subtractive patch sound source
00:04:55 Stereo Enhancement Traditional stereo panning
00:06:13 Stereo Enhancement Spectrally transparent waveshaping
00:07:22 Stereo Enhancement dåpf inputs/outputs
00:09:42 Stereo Enhancement Controls and CV inputs
00:10:14 Stereo Enhancement 6dB/12dB pole switch
00:11:18 Stereo Enhancement Mono to Stereo patching
00:15:41 Stereo Enhancement Static phase shift
00:17:32 Stereo Enhancement Level 1: modulation
00:19:40 Stereo Enhancement Level 2: modulation + waveshaping
00:25:02 Stereo Enhancement Level 3: modulation + timbre
00:27:50 Vibrato Everything
00:28:17 Vibrato Everything What is vibrato?
00:29:35 Vibrato Everything NonFM vibrato
00:30:22 Vibrato Everything (tangent: sine phase)
00:31:34 Vibrato Everything (tangent: sine spatialisation)
00:32:37 Vibrato Everything NonFM vibrato (sine wave)
00:34:11 Vibrato Everything NonFM vibrato (sawtooth wave)
00:38:42 Vibrato Everything NonFM vibrato (complex audio)
00:40:46 Vibrato Everything NonFM... FM? ...PM! (Phase Modulation)
00:43:47 Feedback Processing |"Doppler"
00:44:33 Feedback Processing |"Doppler" Lúbadh feedback patch
00:46:38 Feedback Processing |"Doppler" Doppler shift description
00:48:08 Feedback Processing |"Doppler" Doppler dåpf 1pole/2pole
00:49:20 Feedback Processing |"Doppler" Doppler dåpf 3pole/4pole
00:51:28 Feedback Processing |"Doppler" Doppler dåpf in stereo!
00:52:02 Feedback Processing |"Doppler" Delay feedback
00:54:54 Feedback Processing |"Doppler" Audio rate modulation
00:56:32 Building a phaser Deep dive into allpass filters
00:58:44 Building a phaser Phase shift of a fundamental
00:59:41 Building a phaser Quadrature: sine | cosine
01:00:43 Building a phaser Drawing perfect circles
01:01:41 Building a phaser Drawing (non)perfect circles
01:02:16 Building a phaser Frequency dependent phase shift
01:04:22 Building a phaser 1V/octave tracking
01:07:40 Building a phaser More than one sine wave
01:08:58 Building a phaser The harmonic overtone series
01:10:19 Building a phaser Sawtooth wave lowpass filtered (reference)
01:11:15 Building a phaser Phase shifting harmonic overtones
01:15:42 Building a phaser Inside a phaser
01:18:00 Building a phaser Stereo Phaser
01:22:19 Building a phaser uPhaser Befaco FXBoy
01:23:46 Building filters Anypass filter?
01:25:05 Building filters RC lowpass filter
01:26:03 Building filters Spectral cancellation principles
01:28:35 Building filters APF to LPF
01:30:10 Building filters APF to HPF
01:32:03 Building filters Parallel dual allpass filters
01:37:41 Building filters Resonant filters