How do Drum Synths work

Im curious to know. The Rhythm has an analogue synth engine. Yet it mostly only produces drum sounds. Why not pads like a Prophet for example. If they have oscillators whats going on in the circuitry that stop synth sounds at a few nice synth sounds but not much more. Obviously they are aimed at drum synthesis but how so? Why cant they do more sound design on the synth(trad) part? Just curious.

The oscillator sections are mostly arranged with drum synthesis in mind. They have “built in” decay envelopes so their output falls away, typically quite quickly. Many of the Machines output noise rather than tone, which can be useful in pads but is typically more appropriate for drums (which are often wide-band sounds).

Interestingly, the default amp envelope is full volume for as long as the pad is held, which is much more like a pad envelope. The quick “drum” envelopes come from the oscillator decays.

The 2VCO machine can make pad-like sounds, if you turn the oscillator decays up to’s tuning isn’t as stable as in many synths.

Also, most synths can make drum sounds. People regularly talk about how great the DN and A4 are for drums. I used to make percussion with an MS-10.

The main features of drum sounds are near-instant attack, fast decays and release - ideally exponential, more use of wide-band sound and spectrum or pitch sweeps, rather than steady or slowly-transitioning fundamentals+harmonics.


Thanks for that detailed response. So the envelopes are the main reason due to attack and delays. There seems to be a lot of similarities with the A4. This is one of most interesting drum machines as it can do synth stuff quite well. Plus the sample playback which is a different topic. Are the oscillators the same type in the A4 and AR do you know?

You can get a great insight in drum synth by taking a look at the DFAM’s architecture:

  • Two Oscs that can FM each other

  • A VCF and a VCA

  • Three decay envelopes, one for pitch, one for the VCF and one for the VCA

So yeah, decay envelopes are key to a good drum synth.

I suspect too that the envelopes’ curves are slightly different to the typical curves you would get on a more bread and butter synth made for playing melodies. Envelopes with an exponential curve always sound more natural for percussive sound than linear ones to my ears. An example of a great tool for percussive sounds is the vactrol low pass gate which acts as a combined LPF and VCA that has a very natural (exponential) decay when you ping it. These low pass gates made the famous “buchla bongo” sound. So yeah, envelopes have to be selected and tuned carefully because they are a big part in how your drums will sound. And not all synth make drum sounds, due mainly to the envelope behavior.

Also, another detail is that if you want your sound to be similar everytime it is produced, the VCOs have to be synced to the trigger, otherwise you get some sounds that get duller than others and it sounds super weird on a 4/4 kick that you want to be steady.


Envelope curves.

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A4 has no sample playback, different analog synthesis to AR, AR machines are dedicated mini synths, A4 has waveforms which can then be shaped (arguably to a greater degree than AR).

Typically on AR kicks are made from pitch swept oscillators, usually triangle or sine, some have noise and FM or ring mod too, similar for snares and rimshot, toms are damped sine wave with mixed noise, hats and cymbal are clusters of square waves with band pass filtering to remove low frequency content, clap is bpf noise with a ratcheting type envelope, cowbell is 2 mixed square waves, and so on.

Each has machine specific parameters, such as sweep time and depth, tuning etc, but then you can also use the LFO, envelope, filter etc to further shape the sound.

You also have the dual vco, noise, and impulse engines which can be used on certain tracks instead of the dedicated drum machines. The noise and impulse can be used to make more conventional early drum machine sounds, amongst other things when used with filtering etc. For example a lot of kick sounds are made by an impulse into a filter close to self oscillation, every time the impulse “excites” the filter into ringing out, the frequency of the filter will determine the pitch and the resonance will determine the decay.


Cheers. The A4 has a great kick. What limitations do you know on snares and hi hats or closed hats and others? Are they harder to synthesize on the A4?

It can be done, bending over backwards:


Thats pretty darn good. Nice Curry case too :slight_smile:

The Tempest can be used for pads and other synth sounds, too. Makes quite a nice 6-voice poly:


It probably takes a bit longer becuase the A4 is not a specialised drum machines, but it’s possible to synthesize nearly any drum sound. I don’t bother starting from scratch myself though, I use @taro’s MOD drums and FM drum sounds as starting points. Check out the samples on his pages for an idea of the breadth of sounds possible.


Those sounds are really unique;

Not really, I made a drum pack of most commonly used drum and percussion sounds called Druma:

Floppy disk pirate and Taro have also done drum packs too.


Most important thing if you want to make drum sounds with a synth is a noise generator. If a synth has that, it can be used as a drum synth. If they made an MS20 with multiple voices and a sequencer, it would be the best drum synth ever made. Never mind how impractical a patch bay for each different voice would be, hah.

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The rytm cymbal and hi-hat machine uses six oscillators, so the sound is much richer than the cymbal and hi-hat sounds synthesised on the A4.

However, the A4 is good at creating metallic sounds as it can modulate the amplitude of the oscillators.