The operators here have fewer knobs than the real ones, on purpose.Follow the signal from left to right. Hover over the inlets/outlets to read the names.

Clock keeps time and does nothing else. It sends a pulse on every 1/16 note, so at 120 BPM you get eight pulses a second. Nothing else in the patch has an opinion about tempo. Take the clock away and everything stops.

Step Sequencer advances one step per pulse and puts out two different things on two red ports. The gate is a trigger: on/off. The cd is a level: this step's value, held until the next step. Both are control data, which is why both ports and both cables are red, and why both labels contain "cd".

Oscillator is the only operator making sound, and it never stops. Everything after it decides whether you actually hear anything. The sequencer's cd arrives at its pitch input, where 1.0 means exactly one octave up. That is the modular 1 volt per octave convention, and it is literally how Oscillator MOP works: a pitch of 0 gives you the base frequency, 1 gives an octave, and 1/12 gives a semitone.

Envelope turns a trigger into a shape. When a gate arrives its output rises to 1 over the attack time and falls back to 0 over the decay time, exponentially, the way a plucked string decays. In TouchDesigner this is the Simple Env MOP , which fires whenever an incoming signal rises across its threshold.

Amplitude multiplies the audio coming in by whatever its cd input tells it. This is the reason you hear notes instead of a drone, remove it and experiment.

Lowpass Filter removes the frequencies above its cutoff and leaves the ones below. Sweep the cutoff down and a bright saw turns dark. Its cd input lets a control signal push the cutoff around, and the CD Amount slider decides how far.

Audio Out ends the chain. One per patch, so sum your sounds first and then send. If a MOPs patch is ever silent, this is the documented first place to look. Is it on, and is it turned up?

That is the entire rule set. Red is control data, white is audio, and every control data port has "cd" in its label. You can read any MOPs patch with it.

Same rules, three voices. This patch has no oscillator, no amplitude and no filter, because a drum voice already has all of that packed inside it. What it does have is more of everything else: one clock driving three separate sequencers, each with its own pattern.

One clock, three sequencers. An operator's output can feed as many inputs as you like, so a single clock keeps all three patterns locked together. They each advance on the same pulse. What differs is which steps have gates on.

Two cables per drum. Each sequencer sends two things to its voice. The cd gate triggers the hit. The cd output sets the velocity.

Kick is a short tone whose pitch drops fast. That drop is the entire trick. Start it 70 Hz above 50 Hz and let it fall in 35 milliseconds and your ear hears a kick drum rather than a beep. Pitch Env controls how far above it starts, Amp Decay controls how long it rings, and the waveform switch moves you from a round sine to a grittier triangle to a harder wavetable body.

Snare / Hat is two voices in one operator, since drums are almost always sequenced as a pair. The snare is a short tuned body mixed with a burst of white noise, and the noise is the snares. The hat is the same noise, filtered much brighter and cut off much faster: a few tens of milliseconds is a closed hat, a few hundred is an open one. It takes four control cables and puts out two separate audio signals.

4ch Mixer is the operator that lets a patch have more than one voice. Four audio inputs, four levels, one output. Balance is real work here.

Audio Out. One per patch, as always. This is exactly the case the MOPs documentation is warning about when it says to sum through a mixer first rather than scattering audio outs around a network.

This is the first patch here that sounds like a piece of music rather than a demonstration. The melody chain from the first lesson and the drum network from the second are both running, off the same clock, summed through one mixer.

Stereo Delay repeats the melody, quieter each time, locked to the tempo. Left and Right each hold their own division of the bar: 1/4 is a beat, 1/16 is one sequencer step, and 1/3 and 1/6 are the triplet divisions. Set both sides the same and the echoes sit in the middle. Set them differently, 1/8 against 1/4 is the default here, and the repeats spread out and cross each other. Notice that nothing is patched into it except audio. It follows the clock because it reads the tempo the way every tempo synced thing in TouchDesigner does, from the project's own clock rather than from a cable. Move the BPM and the echoes move with it.

Sidechain ducks whatever passes through it every time a gate arrives, then lets it back up. This is the pumping under almost every dance record, and the thing worth understanding is where its trigger comes from. It is the same gate that fires the kick, not the kick's audio. A real sidechain compressor listens to another signal's loudness and needs a threshold. The trigger version needs neither, and because it is driven by the same red cable as the drum it locks perfectly. Duck sets how far down it goes. Decay sets how long the climb back takes, which is what makes it groove instead of stutter.

Follow the kick sequencer's gate cable. It leaves one red port and arrives in three places: the kick, the melody's sidechain, and the hats' sidechain. One output can feed as many inputs as you like, and this is the patch where that stops being trivia and starts being the arrangement.

Two things about order. The sidechain sits after the delay, so the echoes pump too. Put it before and the delay simply fills back in the gaps the ducking just made. And both sidechains sit before the mixer, because ducking after the sum would duck everything, including the kick that caused it.