Envelopes controls how the amplitude, the frequency or the filter changes over time.

Amplitude Envelopes

Theese envelopes controls the amplitude of the sound. In ZynAddSubFX, amplitude envelopes can be linear or logarithmic. In the next image, it is shown the differences between theese envelopes.
    Amplitude envelopes

       The amplitude envelope is divided into:

Frequency Envelopes

Theese envelopes controls the frequency (more exactely, the pitch) of the oscillators. The folowing picture draws the stages of theese envelopes.
    Frequency envelopes
The dotted line represents the real pitch of the sound without the envelope.
The frequency envelopes are divided into 3 stages:

Filter Envelopes

Theese envelopes controls the cuttoff frequency of the filters and are divided into:
    Filter envelopes

Freemode envelopes

    For all envelope there is a mode that allows the user to set an arbitrary number of stages and control points. This mode is called Freemode.
    Free mode envelopes
    Only stage that always remains defined is the Sustain, where the envelopes freezes until a Note Off event.

User interface

       All the envelope types has some common controls:

       The parameters for Amplitude Envelopes for ZynAddSubFX are:
        Amplitude envelope
       For Frequency Envelopes the interface has the folowing parameters:
       Frequency envelopes

       Filter Envelopes has the parameters:
       Filter Envelopes

       The Freemode envelopes has a separate window to set the parameters and controls:
       Freemode envelopes