Mod Envelopes let you control a specific parameter in Atom, by a pre-determined amount. By adjusting the Attack, Decay, Sustain and Release values you can decide how your modulation is applied, which helps immensely in making a wide variety of sounds.
The Mod Envelopes are found on the top right of Atom, and the two envelopes work independently from one another:
To turn on a Mod Envelope simply click the grey light in the top right of the desired Envelope section to turn it pink (which means its on):
Clicking the light again will turn the Envelope effect off.
Each mod envelope has it's own ADSR section. The "A," value sets the envelope's Attack, or how quickly the modulation will begin. Higher A values mean the modulation will take longer to get started.
The "D," value sets the envelope's decay, or how quickly it will reach the sustain. The higher the D value the longer it will take to reach sustain.
The "S," value sets the envelope's sustain amount, or what setting the modulation will have once it's reached its sustained value.
The "R," value determines how quickly the modulation stops once the process ends. Higher R values mean longer release times for the modulation process once it ends.
Each Modulation Envelope has 3 destinations you can select, which tell Atom where you want the modulation to apply to. To select a modulation destination click the grey box and select a parameter from the dropdown menu:
In the above example we've chosen to have Mod Envelope 1 affect filter cutoff.
The amount of modulation that gets applied is controlled by the destination knob to the right of the destination source. The more this knob is turned to the right the more aggressively the modulation you've created will be applied to that parameter:
To bring the modulation back to 0 double click the destination knob, which will bring it to 0 (essentially pointing straight up).
Each modulation envelope can have 3 destinations applied to it, meaning three different parameters in Atom can be modulated by a single mod envelope.