VCVRackTutorial: Using modulated delay times in VCV Rack

This is a method of patching and modulating delays I find so compelling I felt moved to write about it. This is all done in the software modular system VCVRack, and assumes you have a basic working knowledge of it. It involves the VCV Router plugin, which is non-free plugin from the makers of VCV Rack, but I consider it a mandatory purchase.

As a start, consider this simple patch:

VCV Rack Patch (right click or command click to save)

This is a single voice sequenced by a Fundamental SEQ-3 Module. Clock triggers sequencer, clock sends pitch to oscillator and gate to envelope. Envelope modules volume of oscillator signal via a Fundamental VCA-1. The only remotely complicated part is in the middle where the pitch signal is captured in a Sample & Hold, triggered by the gate from SEQ-3. It’s then quantized by a JW Quantizer and transposed by a Fundamental Octave module.

Now, add a delay. In this case an AS Delayplus:

VCV Rack Patch (right click or command click to save)

This sounds fun, and you can play with delay time and feedback. As it happens this delay module models actual analog delays to the extent that changing the delay time affects the pitch of the delays. If you load this patch you can hear this by turning the delay time knob.

What I’m interested in here is to set up a tempo synced delay. The AS BPM TO Delay Calculator can help out there. Drag the delay time all the way counter-clockwise (it will display 1 MS) and then feed the output of a particular delay time from the BPM Delay/MS Calc:

VCV Rack Patch (right click or command click to save)

Now the delays fall in the rhythmic grid, in this case, a dotted quarter note after the dry signal from the VCA. The fun begins when you modulate the delay time. In this case I use 4 different outputs from the BPM Delay/MS Calc, for dotted half notes, dotted quarter notes, dotted 8th notes, and dotted 16th notes. You can select different delay times by clicking on the ‘Clock’ button on the Fundamental Router 4:1.

VCV Rack Patch (right click or command click to save)

Now comes the fun part. I add a Hetrick Random Gates module, and send it the gate output of the SEQ-3 to trigger it. I also turn down the Max knob on the Random Gates so that only gates 1/4 are triggered. I then feed the first 4 trigger outputs on the Random Gates into the ‘Sel’ inputs on the Router 4:1. What is the result? Every time a new note is triggered by SEQ-3, a different delay time is randomly selected.

VCV Rack Patch (right click or command click to save)

What is the result? Something rhythmically and harmonically interesting — it’s continually changes, and each time the delay time changes, it changes the playback speed and pitch of the delayed signal. Now, since we chose 4 differented dotted note delay times, they each have a relationship that is both harmonically and rhythmically coherent. A dotted 16th note is 1/8th as long as a dotted half note, and if you switch between them, the frequency jumps by a factor of whole octaves. In the case of dotted 16th to dotted half note, the transition drops the pitch by 4 octaves. If you haven’t considered the math involved it’s exponential: Twice the time or frequency, increase by one octave, 4 times the time/frequency, increase by two octaves, etc.

It gets even more interesting if you don’t choose delay times that are multiples of each others. Say, use dotted 1/2, quarter note, dotted 8th note and 16th note. The dotted half note is 3/2 the time of a 1/4 note, a dotted 8th is 3/2 of a 16th note. Now as it happens, the pitch releationship of 3:2 is a major 5th, so when the delay time changes it also changes the pitch by an interval that is musically interesting! I haven’t worked out all the pitch relationships between different note durations, but listening to the output, it always seems to add up harmonically, no matter which note duration you choose.

Here’s an example of the output of this last patch. While recording, I tweaked the sequence a little bit as it played.
Download audio file here (left- or command-click)

Reaktor Effect: Random Multitap Delay/Shuffler

The Random Multitap Delay is a delay effect that randomly, continuously changes the delay time between the input and output. The delay times are based on musical note durations – ¼ note, ? note, ? note triplets, etc.  My goal was to use random processes in a way that preserves rhythmic integrity — the output stays in time with the input and any other rhythmic elements in the music.

Internally there is a multitap delay, whose delay time is a multiple of the current rhythmic division. If you select ? for the tap length then the first will delay ? note, the second 2/8 , the third ? etc.

The effect switches randomly between the delays over time, effectively re-arranging the input signal in time, shuffling it up.  This is particularly effective on drums, because it will generate an endlessly varying rhythmic pattern that will still add up to the ear.

There are two identical delays for the left and right sides of the stereo signal. Since the current delay tap is chosen randomly, the right and left signals will be different even if all the controls are set the same.

It’s actually harder to describe what the effect does clearly than to understand what it does by tweaking the controls, and hearing the results.

In Use

There is a hierarchy of chaos in the controls of the Random Multitap Delay.  I’ll list them from least chaotic to most chaotic:

Sync and Stepped On

With both sync and stepped set, every rhythmic division, one delay is selected.  For example, if 1/8th is selected for tap length and 1/8th is selected for S&H, every eighth note a different delay tap is chosen.

Sync On, Stepped Off

Every rhythmic division a fractional value is chosen, that will select a blend of 2 delay times.  For example, if the tap length is 1/8th and selection value is 3.5, you will hear a 50/50 mix of the 4/8ths and 5/8ths delays.

Sync Off, Stepped On

The delay tap selection varies continuously, based on Rand Speed, but only one delay tap is selected at a time.

Sync Off, Stepped Off

The delay tap varies continuously at Rand Speed, and a mix of two delay taps will be heard all the time.

The meter and numeric display below the stepped button shows you how these controls interact.  They will show you exactly which delay tap is playing at a given time.  The delay taps are numbered 0 to 7, since I’m a computer programmer ;-)


Tap Length

This chooses a base delay time for the multitap delay.  These are standard musical divisions of time — ¼ note, 1/8th note, dotted 1/8th etc.


Controls the rate of change of the delay taps.  Every ¼ note (for example) a new delay tap is selected at random for the output.


When this is on, the delay time is selected based on the setting of S&H.  When it is off, the delays are switched between continuously at the rate specified by Rand Speed.

Rand Speed

Chooses the speed at which the delay selection changes. The numeric value below the knob gives the speed in cycles per second/Herz.


Determines whether the delay selection is stepped (i.e. selecting just one tap at a time 0, 1, 2, 3…) or continous.  If Stepped is off,  you will hear a mix of two adjacent delay taps most of the time ( 0.3, 1.7, 2.1 …)


Controls the level of feedback for both the left and right delays.

Cross FB

Controls the amount of the left delay that is fed into the right delay, and vice versa

L FB Mode/R FB Mode

Selects the filter that is included in the feedback path of the delays. High Pass, Band Pass, Low Pass etc. ‘Bypass’ is also an option, which removes the filter entirely from the feedback path.


The difference between the left and right feedback filter cutoffs.  At 12 O’Clock, L & R filters have the same cutoff. As you rotate left, the left cutoff reduces, and the right cutoff increases.  As you rotate right the left cutoff increases and the right cutoff decreases.


Feedback filter frequency


Feedback filter resonance.