Drum Synthesis

This is a topic which many people have spent endless years working on, but it is always nice to revisit as new sounds become popular and new synthesizers arise. First let’s talk a little bit about drums themselves and what it is that makes them tick…

When you listen to the typical drum beat, the three most common elements are kick drum, snare and hi-hats. What defines the three main elements, and what jobs do they fulfill?

  • The kick is short to medium in decay and low in frequency.
  • The snare is short to medium in decay and midrange/ full-range
  • The hi-hats are short in decay and high frequency.

When we consider the other non hi-hat cymbals (long decay, high end frequencies), toms (medium to long decay, low end frequencies) and other percussion like a cowbell (short decay, high frequencies) we can start to see how the typical drum set is very logically built. Again, each element serves a purpose in time and frequency domain. This relationship is nice to keep in mind when mixing drums too as it can help you determine how to EQ, compress, gate, etc.

Now to the synthesis.

Modern productions use sampling, acoustic drum replacement, true analog style drum synthesis and myriad other ways to create percussive tracks. Basically, anything goes. That is the beauty of synthesizing drum sounds from scratch since you can’t really be wrong. Often intuitively people will hear a sound with the above mentioned characteristics and place it into a category. A person saying “Boom” is a kick drum, saying “Bap” is a snare, “t-t-t-t” is a hi-hat beat.

There are a few ways in which I synthesis drum sounds; Logic Audio’s Ultrabeat, Kontakt, and my Korg ESX. The former are more flexible, but the latter is more fun.

When I synthesize drums I like to think of the big picture and keep in mind the space that each element occupies.

Most analog style, synthesized drums have a pitched tone (often sine waves) and an attack tone. Along with the pitched tone and attack, snares often have a rattly sound which is added by the metal “snare” rattling on the resonant head. Cymbals are more often than not composed mainly of noise which is a combination of many tones without any particular pitch.

Kick drums generally have a nice low end element which is easy enough to create by using a sine wave at around 50-90Hz, and often they have a slow pitch drop. Highly resonant filters can also artificially create 808 like tones. The attack is a little more complex. It can be created by adding a very short 5-30ms static type noise to help create some articulation. With certain styles like Psy-Goa, the zap like sound of a quick pitch drop or resonant filter sweep can add the attack. Toms are almost the same as kicks, yet they are higher in pitch.

Snares usually need some rattle to differentiate them from Tom tones. This can be a simple noise, or very fast pitch modulation. Snares do have an attack tone, but since the attack is often a noise oscillator and snares have a noise component, what we need to think about it the volume envelope of the noise. It should start rapidly at full volume then quickly drop to about half it’s volume in about 5-30ms, then decay over a period of time that you want the snare sound to last for.

Many times for hi-hats I just pitch up a snare sound and put a high pass filter on it. The snare has the noise type properties that hi-hats need, pitching them up shortens them in length and the filter knocks off the low end frequencies.

I would suggest playing around with the decay length of your drums in real time. It can add interest to your static drum loops. One nice way to automate this is to add a random LFO to the decay of the drum. It can also be good to assign the velocity to decay since real drums decay for longer when they are struck harder.

So there you are, some basic synthesis techniques and analysis.

Here is a nice document which explains some of the more well known synth drum’s architecture.
Waldorf Attack Rack

Check out this nice video from dubspot which explains a little bit about using Ultrabeat to synthesize different drums.
http://youtu.be/VYlsOGnAkFc

This Gearslutz thread has some good info plus links to a whole series about drum synthesis from Sound on Sound magazine Here

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