Making Music
  Computer Music Software and Hardware

Multi envelopes

As digital technology progressed, the multi-segment envelope appeared. This let you specify both time and volume levels for each stage of the envelope and as most processing was done in cheap software rather more expensive hardware, it was easy to dial up six, eight or more segments according to your desire for complexity.

One feature of multi-segments envelopes is that they allow you to create a contour that rises, falls and then rises again in volume.

Envelopes and amplifiers

Whatever shape the envelope might be, you won't hear any sound at all until it's fed to an amplifier. In a synthesiser, the envelope controls the amplifier so the greater the envelope's amplitude during any phase, the more the amplifier opens and the louder the output will be.

Modular machinations

Although envelopes are primarily used to shape the volume of a sound, in a modular synthesizer you can connect it to other modules, too.

Let's assume we're using the archetypal ADSR envelope.  Let's see what happens if you apply it to the cutoff control of a low pass filter.

We usually don't want an envelope to control the harmonics of a sound in such a severe way so filters usually have a control to determine how much of the modulating signal is used. This is a very useful feature because it's common for the harmonics of an acoustic instrument to change as its volume changes. Brass instruments, for example, generally become brighter as they are played louder.

You can also plug an envelope generator into an oscillator. If you look at the ADSR illustration, you can probably work out what sort of pitch changes the envelope is likely to make. As with filters, an Amount control will reduce the effect from a mad siren to a blip. It can be used to add a slight pitch lift that occurs at the start of many notes in wind and brass instruments, particularly in jazz.

With our Quick Guide series on Oscillators, EQ and Filters and now volume shaping with envelopes, we have covered the essentials of the three basic synthesis building blocks. Putting them all together is the art of the game.