Mr Corvest has become a somewhat prolific developer in the iOS world since he first appeared. His latest creation is FAC Envolver.

The app is an envelope follower, this implies that it tracks the contour of the input signal and builds a corresponding envelope. Think of the envelope as the outline of the graphical representation of a rectified version of your input signal. By its very essence, it’s exactly what you get. But the process does not stop there and gives you the ability to modify the shape according to a set of provided parameters.

So it’s possible to define the rise and fall time as well as the depth of the envelope or also to invert it. Those parameters are the key to ensure the flexibility of the effect, and to meet the goal you are looking for.

The previous lines are more a general presentation of what an envelope follower does, but the particularity of FAC Envolver, which makes it an outstanding and versatile tool, is that it delivers the envelope via MIDI control change messages or commonly referred to as CC.

The key is to map the CC number parameter to the volume, cutoff, resonance control of your synthesizer or effect units. By doing so you will get instant additional hands to tweak your parameters automatically depending on what you are currently playing.

The internal signal path is built around two independant channels, having one envelope circuit detection per input signal. So the left input signal is wired to the envelope one, and the right input signal is wired to the envelope two.

FAC Envolver will breathe life into your sound, providing interesting natural modulation that will always be different by nature. Following the diagram below, the sound flows from the left to right or from the input to the output.


  • Gain (up to 15db) Use it carefully
  • Audio output activated or mute
  • Monoize input signal for detection
  • [ON] Mono for each env
  • [OFF] Left for first env and Right for second env

Output envelope 1 (L) and 2 (R)

  • Mute – left buttons (|1/ or |2/) are toggleable (gray muted/yellow activated)
  • Rise – defines the time the envelope takes to rise. Set to minimum to catch the transient.
  • Fall – defines the time the envelope takes to fall. Set to maximum for more slew between peaks
  • Depth – provides attenuation or amplification of the envelope
  • Multi-waveform graph – envelope contour layered over input signal. Touch the graph to freeze the display temporarily.
  • Invert – invert the envelope
  • CC# – number of the control change messages where the envelope is sent (channel 1). Only one CC can be used at time per output.

FAC Envolver costs $6.99 on the app store now