A sampled drum kit is a set of recordings. Each hit is a fixed piece of audio, and when you change its pitch or its length, you are stretching or trimming that recording. An analog drum machine has no recordings in it at all. Every hit is a small circuit being kicked into motion, and the sound is whatever that circuit does next.
That difference is not nostalgia. It changes what the controls can do. When the sound comes from a circuit, turning a knob changes the circuit, so the drum itself changes shape rather than a playback of it being bent. What follows is how the three families of circuit in an analog drum machine work, using the voices and control names of Rhyth-O-Matic, a sixteen-rhythm analog drum machine with eleven drum voices and nothing sampled.
Three circuits, eleven voices
Rhyth-O-Matic's eleven voices are bass drum, snare, rim shot, closed and open hats, cymbal, cowbell, claves, maracas and two congas. They are not eleven unrelated sounds. Most of them come from one of three kinds of circuit, and once you know which, you can predict what each one will do when you touch it.
Resonators: the drums and congas. A resonator is a circuit that rings when it is struck, the way a drumhead or a tuning fork does. Give it a short pulse and it swings back and forth at its own frequency, losing a little energy on each swing until it dies away. In Rhyth-O-Matic the drums and congas are resonators that ring and fall in pitch: the note starts slightly high and sags as it decays, which is a large part of what makes a kick sound like a kick rather than a beep. Two things define a resonator's sound, how high it rings and how quickly it stops, and those are exactly the two things a drum voice needs to be adjustable.
Filtered noise: the snare rattle and maracas. Noise is every frequency at once, with no pitch. On its own it is hiss. Pass it through a filter and give it a short envelope and it becomes the rattle of snare wires or the shake of a maraca: a burst of texture rather than a note. In Rhyth-O-Matic the snare rattle and the maracas are filtered noise, which is why they sit in the kit as grain and air rather than as pitched hits.
Square waves through band-pass filters: the metal. Cymbals and hats are hard to make from a single tone because real metal rings at many frequencies that are not neatly related to one another. The analog answer is to stack several square-wave oscillators, each at its own pitch, so their harmonics pile up into a dense, clangy cluster, then carve that cluster with band-pass filters to pick out the part that sounds like a hat, a cymbal or a cowbell. Rhyth-O-Matic's hats, cymbal and cowbell come from six square-wave oscillators through band-pass filters. The metallic, slightly synthetic edge of those voices comes straight from that construction.
Why TUNE and DECAY behave differently here
On a sample, a pitch control usually speeds the recording up or slows it down, and a length control cuts the tail off or fades it. Push either far enough and you hear the process: chipmunk transients, a tail that ends abruptly. On a circuit voice, the same controls act on the thing that is generating the sound.
Rhyth-O-Matic's EFFECTS panel has TUNE and DECAY for every voice. TUNE changes where a resonator rings, so a bass drum pitched down is still a bass drum with a clean attack, not a slowed recording of one. DECAY changes how fast the circuit loses its energy, so a longer decay is a drum that genuinely rings on, and a shorter one is a drum that is damped, not a tail that has been clipped. As the product page puts it, that is why TUNE and DECAY "reshape every sound continuously instead of stretching a recording."
A practical way to hear this: take the bass drum, pull DECAY long and sweep TUNE down. The note keeps its falling-pitch shape all the way, because that fall is part of the resonator's behaviour rather than something baked into a file. Then do the same to a hat or the cowbell and listen to the band-pass filters move through the oscillator cluster instead.
After the voices, the same panel has processing for the whole kit: FUZZ, CRUSH, TONE, REVERSE, a tempo-synced DELAY with TIME and FEEDBACK, and a spring reverb, with a dry/wet MIX and an ON key. CRUSH with a dark TONE takes the kit toward lo-fi; REVERSE with a long DELAY takes it somewhere stranger. Because the voices underneath are circuits, those effects are working on sounds you have already shaped at the source.
Where the feel comes from
A circuit makes the sound; the rhythm and feel controls decide how it is played. The front panel has VOLUME, BALANCE, SWING, ACCENT and WEAR alongside the TEMPO dial (40 to 240 BPM) and its beat lamp. BALANCE trades the drums against the percussion. SWING drags the off-beats toward a shuffle. ACCENT sets how hard the marked hits push. WEAR makes the unit play like a well-used box, loose and tired rather than tight and clean.
The sixteen rhythm keys can also play two patterns at once, each on its own grid against the same bar clock, so a 16-step rock can run under a 12-step shuffle. That is a subject of its own; the short version is that the lopsided results are exactly why these boxes were loved.
It is an instrument, not an effect, so load it on an instrument or MIDI track. With HOST SYNC on it follows your DAW's tempo and bar, and every voice also plays from MIDI on the General MIDI drum map (36 kick, 38 snare, 42 hat and so on), so you can program your own parts on the same circuits. It runs as AU, VST3 and AAX on Mac and VST3 on Windows.
To hear the circuits for yourself, start a 14-day free trial of the full version and put Rhyth-O-Matic on an instrument track. Load the Dusty Break preset, open the EFFECTS panel, and sweep the bass drum's TUNE with a long DECAY, then the cowbell's, and listen for the difference between a ringing resonator and a filtered cluster of square waves.