Analog drums/percussive synthesis

Learn about percussive instrument synthesis using Eurorack modules patched following different audio synthesis techniques.

Percussive instrument synthesis

Percussive synthesis originates from experiments to mimic real drums by breaking them down to different basic layers and playing them using electronic circuits.

Drum machines and Eurorack drum modules

Percussive instrument synthesis became popular in the 80s when electronic music became mainstream with invention of Roland TR-808 and TR-909 drum machines. They contain a pack of sounds for complete percussion needed for the song packaged to a single machine together with a easy to use sequencer to program them.

We have developed two compact percussive Eurorack modules. Compact module with two kick drums based on original 808 and 909 kick circuits, as well as module generating analog snare and hi hat sounds based on original 808 circuits. These drums can be triggered by a simple 5V on-off gates:

Our classic drum modules produce great sounding classic drums and cymbals from original circuits rebuilt using latest high end components  in affordable small 9PH Eurorack module packages.

Synthesizing percussion from scratch using our Eurorack modules

We can synthesize these kicks, snares, hi-hats and other percussive instruments using our oscillator, filter and amplifier Eurorack modules.

Custom percussive instrument synthesis requires more space in Eurorack synthesizer but it offers more control options opening door to unique sonic possibilities.

Analog drum synthesis

Drum type percussive instruments mainly consist of body layer – one or several membranes which when hit resonate at certain frequency with a specific pitch sweep.

Drums often also have initial punch layer – high pitch noise that quicky fades as soon as the drum sound is triggered. Before mixing initial punch layer has to be filtered or equalized to remove low frequencies so they wouldn’t interfere with frequencies present in the body layer.

Highpass filter

To generate drums we firstly need to convert gate input to several fast decaying envelopes that start to decay as soon as the gate is initiated.

This can be done with a ADSR envelope generator module or gate to pulse converter patched to envelope follower that gets triggered with a pulse and starts decaying immediately.

Kick drum synthesis

Bass kick drum is among the easiest to synthesize as it consists of a single membrane.

808 style kick synthesis

To generate 808 type drum we can use a filter with resonance set close to self oscillation level. Original 808 kick uses T shape resonator circuit that is essentially a band pass filter with a high Q level (resonance).

When sending pulse signal to it we initiate the resonation that generates naturally decaying sine wave. Frequency of such kick sound can be controlled with filter pitch knob and its decay with filter resonance knob.

To achieve a click at the beginning of the kick sound we can patch a second very fast decaying envelope to FM control of the filter. For a brief moment it would increase the frequency of the kick generating high pitch click at the beginning of the sound.

Click sound can be improved by sending fast decaying wave form instead of envelope to filter FM input. For this we can use one of the wave forms from the oscillator. Patch it to the VCA together with envelope to get fast decaying tone and patch its output to the filter FM. This would generate frequency modulated kick click that has many different options depending on the waveform used.

Our analog filters

909 style kick synthesis

909 kick uses triangle oscillator wave instead of filter. VCO offers better pitch stability and precise envelope control. We would have to patch triangle wave oscillator output  and envelope to VCA to control sound decay. Second envelope would have to be patched o VCO exponential FM input for initial click sound. In 909 kick triangle wave is rounded up using soft clipping distortion.

Oscillator phase would also have to be reset at the beginning of the kick sound to make sure that wave form would start from the same point with each kick. This can be achieved by patching pulse signal to VCO hard or soft sync inputs.

909 kick also has noise part, we would need a separate envelope for that. We would have to patch white noise or high pitched FM oscillator sound to VCA together with the envelope and mix the resulting signal with boomy part of the kick sound.

Same as in 808 we can modify the kick by sending fast decaying wave form instead of envelope to filter FM input. Different click timbre can also be generated by mixing for example square and sine waves using crossfader controlled by click envelope. This can be done by using voltage controlled crossfader available in our quad VCA module.

Snare drum synthesis

Snare drum is more complex compared to base drum as it has two vibrating membranes on both sides of the drum.

808 snare synthesis

808 snare is generated from a mix of two T shaped resonators pitched at different frequencies and fast decaying white noise layer.

We can mimic that using two separate filter modules set at different cut levels and same amount of resonance. Same pulse wave would have to be sent to both filters to generate the two decaying resonant sine waves. For click sound we would have to patch the same fast decaying envelope to FM inputs of both filters. As in 909 kick synthesis two VCOs can also be used for the same purpose.

Same as in 808 kick we can spice the snare by sending fast decaying tones to filter FM to generate different kinds of frequency modulated snare sounds.

For the punch layer 808 snare uses white noise patched to VCA controlled with fast decaying envelope.

Mixing the 3 snare layers

These 3 elements would have to be mixed to a single output to blend them into a snare sound output. This can be achieved using our mixer module, apart of simple mixer it also offers soft clipping distortion to spice further spice the sound.

Subtractive synthesis

Cymbal synthesis

Cymbal instruments are generated by modulating metallic noise mimicking sound generated by striking metallic plates.

808 hi-hat synthesis

Metallic noise for 808 hi-hats is generated using additive synthesis by mixing 6 crude square wave oscillators set at specific frequencies. Wave sum is then passed through resonant band pass filter and the resulting sound is muted using fast decaying envelope and VCA.

Our 808 hi hat module provides output of this metallic noise to be used for other custom percussion as well as input to override it to create more unique hi hats.

Synthesizing the metallic hi-hat noise

Additive synthesis using 6 high end oscillator modules is impractical. Similar metallic noise can be achieved using FM synthesis. To achieve it you would have to patch sine or different wave output to one of FM inputs of the second oscillator and then filtering its output signal using band pass filter. The resulting signal would have to be muted by patching it to the VCA controlled by fast decaying envelope.

By using FM synthesis for metallic noise we have much more possibilities for different types of metallic sounds as we can patch different wave forms, set oscillators, also set oscillators at different frequencies, control frequencies with envelopes and LFOs etc.

FM audio synthesis

Custom percussive instrument synthesis

By understanding the concept of membrane body and punch sounds you can build all kinds of custom percussive instruments.

All types of synthesis is useful for percussive instruments

Subtractive synthesis can be used to patch envelope to modulate low pass filter so it would quickly remove high frequency content as soon as the percussion starts.

FM synthesis can generate all kinds of membrane click sounds, also a wide range of sweeping and metallic noises that can be made short with fast decaying envelopes and VCA.

We would also recommend trying out complex audio synthesis to generate more interesting tones that can he used for percussion.

Recording generated sounds as samples

If percussive instrument modulation or analog variation is not required – generated sounds can be recorded and cut into samples to free up Eurorack modules for other use.

These sounds can then be organized into sample banks and played using software or hardware sampler using midi.