Making Music
  Computer Music Software and Hardware

Soft mod

So, we have a natural or manual modulation such as vibrato that can be applied directly to instrument as it is being played, and we have an electronic modulation that is applied to a sound during its creation or during performance.

There is a third type of modulation that involves running audio through a processing unit and modulating it to create an effect such as chorus, flanging and phasing.

There are now so many ways of messing with a sound that it's not always clear or obvious how an effect has been created. In a soft synth or a sequencer's plug-in list you'll often see effects you may not necessarily think of as modulation grouped into the modulation category. It's commonly used as a catchall for effects that don't fit neatly into other categories such as filter, reverb, delay, dynamic and so on.

In practise the category doesn't really matter, but if you know how an effect is produced, you'll know what's happening when you twiddle the controls and be better able to decide what sort of effect you need if you're looking for a particular sound.

All together now

The most common processed modulation effect is chorus so let's see how that's produced. A natural chorus, as mentioned above, is created when several similar, but not identical, sounds are played at the same time.

You can hear a simple chorus effect if you play a sound from two identical oscillators and then slowly detune one of them. The difference in pitch creates an effect known as beating and the 'beats' grow further apart as the distance between the frequencies increases. The result is a cycle during which the two pitches cancel each other out creating a sort of tremolo effect. This beat frequency helps musicians tune instruments to each other.

Even though singers and instrumentalists such as the string section of an orchestra, try to play together and in tune, there are very small differences between them in the tuning, tone and timing and these produce an ensemble or chorus effect.

An electronic chorus effect tries to create a chorus from a solo sound by applying many small, constantly-changing delays, typically around 40-50ms, to the signal and varying their pitch. The result is unlikely to turn a solo singer into a choir or a string line into a string orchestra but the effect is very good for 'thickening' a sound and giving it more substance. The main controls in a chorus unit control the speed and depth of the effect but you may see a whole range of parameters tacked on to a software chorus effect including filter controls to make the sound 'sparkle'.

On the edge

While a chorus unit tries to duplicate a natural effect electronically, other modulation effects such as flanging and phasing are purely electronic.

Flanging, so the story goes, was created when someone played two tape recorders containing the same material and pressed their hand on the flange of one of the tape reels. This slowed down one signal vis a vis the other causing the signals to drift out of phase creating a phase cancellation effect resulting in the characteristic whooshing sound.

To create flanging electronically, you delay the signal by a few milliseconds and mix it back with the original. By varying the delay with an LFO you can control the sweep effect.

Other parameters may include rate which controls the speed, and feedback which may make the sound sharper or more metallic.

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