There’s a lot more to drum grooves than you may realise. Bruce Aisher investigates the psychoacoustics of rhythm programming.

When programmable drum machines became a commercial reality in the early 1980s, two opposing arguments became popular. The first suggested that these early digital drum machines (such as the Linn LM-1 and Oberheim DMX) sounded nothing like a real drummer – in other words, they sounded like machines. The second argument claimed that drum machines would put human drummers out of work.

The reality is that drummers are still very much around, and that the metronomic timekeeping of drum machines and their DAW-based counterparts helped foster whole new genres of music. The convergence continues with tools to make human recordings sound tighter and techniques to make machine-based rhythms less metronomic.

Clearly, a quick and useful way to turn a drum beat into a groove is to apply swing in order to push and pull the placement of drums in a bar. We examined the effects of DAW and drum machine swing in a previous Attack article. Varying swing for different rhythm elements enhances the usefulness of this approach.

Here we can compare a simple beat with straight timing:

1a

And the same beat with moderate swing applied:

1b

 

Swing is predominantly about timing, but in this article we’re going to look at how an understanding of certain psychoacoustic principles can affect our perception of the groove and timing of the beat. In other words, how changes in the level, length, tonality and pitch of parts of a rhythm alter the feel.

Randomisation

Some basic algorithms for creating a more ‘human’ programmed beat rely on randomising the velocity and timing of individual hits. To hear the effects, let’s start with totally rigid velocity and timing:

2a

If we randomise the velocity, we get this kind of effect:

2b

Randomising the timing instead of the velocity gives us this kind of effect:

2c

Randomising both the velocity and timing gives us this kind of effect:

2d

 

This is fine as far as it goes, but in many cases it simply sounds untidy. However, it’s easy to forget that technology itself often far from perfect. Jitter (an irregularity in clocking) is inherent in MIDI, which is only capable of transmitting one note at a time. This means that no drum sounds triggered over the MIDI protocol will ever play simultaneously. Faster interfacing such as USB may also have issues is this department. Research published by the AES as far back as 1994 showed that even the internal clocks on hardware drum machines were wildly variable as far as accuracy was concerned. We’ll revisit this shortly.

15th May, 2015

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