Envelope follower smoothing
  • Hey, does anyone have any tips for smoothing the output from the envelope follower? I'm trying to use it with my guitar to to have an envelope driven filter cutoff but the envelope is too jagged. I've tried a slew limiter but that didn't do it for me. How would I go about generating an RMS envelope or something like that?

  • Yes a slew limiter or the 1-pole LP node.
  • The best method is to use a threshold detection to trigger an envelope - you could never smooth the envelope follower node enough to get an accurate sounding envelope follower pedal. I'm making one for you right now :)
  • Here it is! Will post sound demos later. Look inside for the tutorial.
    Envelope Follower Tutorial.audulus
  • 1st loop: LPF mode
    2nd loop: LPF mode + inverted envelope
    3rd loop: HPF mode
    4th loop: HPF mode + inverted envelope

  • Thanks @biminiroad! Real fun to play with, and close to what I want. What do you think about adding some kind of velocity sensitivity so the envelope height responds to your playing dynamics?

    ps just spent a bit of time trying to get use the RMS module inside the RMS compressor to work for me but you're right, not enough smoothing. An envelope probably is the way to go.
  • How would you add velocity to envelope response?
  • I guess I'm talking about Envelope Amount. The amount that you allowed the envelope to affect the cutoff, and tying that to the guitar volume. With the auto-wah example, the ADSR envelope that you're triggering goes to a max of 1, and then you scale that with a knob, but if I was able to smooth the output from the Envelope Follower node as I'd originally thought, the envelope max would depend on the note volume from the guitar. If you play a loud note, the Envelope Follow traces a bigger curve; if you play a softer note, it traces a smaller curve. So if I have to use a triggered ADSR envelope, then I want to have some kind of peak detection or something to bring that volume tracking back to the envelope.

    The effect I'm trying to build is based off this pedal. They call it a low pass gate. Listening to it I think it's basically a volume controlled low pass filter with no resonance, though I could be wrong.

  • So I've been thinking about this for a while and have come up with another way to do the envelope following, @biminiroad based on what you told me about the waveform node drawing the min and max lines when the waveform changes too quickly for it to draw the whole audio signal.

    This module basically takes the RMS of the audio input, samples and holds the max amplitude over a small time window (the grain size in milliseconds) then passes it through a slew limiter to smooth it out a bit. It's a bit coarse but it seems to work fairly well for guitar. See what you think.

    It occurs to me though that the waveform node is already doing this, and doing it better than me. If it can draw the max line of an audio signal then its already calculating that max envelope. Is there any way that you can recreate the max calculation that it's doing in Audulus? Or, would it be possible in a future update to have outputs from the waveform node of the min/max envelopes to use as mod sources? :)
    Max Envelope.audulus
  • Ah yes, I have a min-max module here that might work for you - you can retrigger the calculations too!
    High-Low Detector.audulus
  • Hi @zilch42, did you ever put this thing together? The Shallow Water pedal? Would love to try it out :) Or if you got any further with the envelope follower module?
  • If you stack envelope follower nodes and then attenuate the signal a little bit you get a pretty usable smoothed envelope. One of the broken preview links below will show you what I mean.

    I don't know for sure what little DSP touches the shallow waters pedal has under the hood, but here is my attempt at combining random pitch modulation with a low pass gate on an envelope follower. I'm calling it "wakes."
    Screen Shot 2018-04-21 at 11.04.17 PM.png
    1407 x 909 - 199K
    Screen Shot 2018-04-21 at 11.04.07 PM.png
    586 x 456 - 46K
  • I thought this was going to be audio based :)