Envelope Generators

Figure 9 - a representation of a Volume Envelope

Now that we have explained the Bass MuRF’s filters, let’s proceed with some more definitions to explain the Animation function of the Bass MuRF.

The term “Envelope” is used to describe the changes that occur to a musical sound, from its start to its end. A musical sound can have a rapid onset, like the plucking of a string or the striking

of a drum. It can also have a gradual onset, like a slowly bowed violin. With the term “Envelope”, the shape of the start of a sound is called the “Attack”. The end of a sound can have different shapes as well – it can be abrupt, like on an organ, or it can be very gradual, fading out like a piano note held down. The shape of the end of a musical sound is called “Decay”. Both Attack and Decay are time-related, and can be measured in seconds or milliseconds. Figure 9 illustrates the components of an envelope.

An “Envelope Generator” is a circuit

that creates a shape

that corresponds to the changes in a musical sound. The signal that comes out of an Envelope generator is sent to a control, such as Volume,

and is used to automatically turn up and down that control to shape the start and end of that musical sound. An Envelope Generator is started by a trigger - a signal used to start the envelope shape.

In the Bass MuRF, there are 8 Envelope generators, one for each filter, that shape the Volume of that filter’s signal. The shape of the Envelopes are all determined by the setting of the ENVELOPE Control. When the Envelopes are started is determined by the PATTERN selected. To understand that, let’s continue.