Implemented Filter Block Envelope Filter -- additional tools requested

austinbuddy

austinbuddy

Axe-Master
Vendor
@FractalAudio also @Admin M@

For the ENV FILTER FILTER1 Block type, it would be useful and great to also have an EQ Bias Detector select tool, that prevents bass strings from dominating the envelope filter detector and equalizes response across strings.

Put another way: "A detector-side frequency weighting (HPF/LPF or tilt) would allow envelope behavior to be normalized across string fundamentals without altering the audible filter response, solving a long-standing envelope imbalance issue at the correct DSP stage." (Thanks ChatGPT)


Right now I have to use two channels /settings- one for Mutron-style enveloper playing on lower four strings, and a second set of settings for the upper 3 strings (especially high register playing).

Since I am NOT a technical person, I worked with ChatGPT to get this extra info if it helps. I did find Chat GPT helpful dialing in tow Mutron-style Jerry Garcia type sounds, but it had to do two separate ones because of the absence of the feature rather than one setting.

Feature Request: Envelope Filter – Detector Frequency Bias​


Context:
The Envelope Filter currently derives its control signal from a broadband amplitude detector. While this works well in general, it produces predictable imbalances with guitar signals where string fundamentals vary widely in frequency and energy (e.g., low E vs D/G/B), requiring audible compromises in sensitivity or sweep range.



Proposed Enhancement: Detector-Side Frequency Weighting​


Add frequency conditioning within the envelope detector path, independent of the audible filter path.


This would affect only the control signal feeding the envelope follower, not the audio signal being filtered.



Suggested Parameters (Fractal-style)​


Detector Low Cut​


  • Type: High-pass filter (detector path only)
  • Range: ~20 Hz – 500 Hz
  • Default: Off (20 Hz)
  • Purpose:
    • Reduce dominance of low-frequency fundamentals
    • Allow envelope to respond more consistently to harmonic content
    • Improve low-string triggering without over-opening higher strings


Detector High Cut​


  • Type: Low-pass filter (detector path only)
  • Range: ~500 Hz – 8 kHz
  • Default: Off (full bandwidth)
  • Purpose:
    • Optional suppression of high-frequency transient bias
    • Fine control over envelope sensitivity to pick attack


(Optional Alternative)​


Detector Tilt​


  • Type: Spectral weighting (shelving-style)
  • Range: −100% (LF emphasis) to +100% (HF emphasis)
  • Default: 0%
  • Purpose:
    • Single-parameter control for detector frequency bias
    • Simplifies UI while providing musically useful normalization


Technical Rationale​


Envelope followers respond to signal energy, not perceptual loudness. Guitar signals exhibit:


  • Strong low-frequency fundamentals on lower strings
  • Higher transient and harmonic energy on upper strings

Without detector weighting, users must compensate using:


  • Global Sensitivity
  • Sweep range limits
  • Multiple scenes or blocks

Detector-side frequency bias resolves this at the correct DSP stage, preserving:


  • Sweep character
  • Resonance behavior
  • Authentic analog envelope response (Mu-Tron / Q-Tron style)


Musical Benefits​


  • More uniform envelope response across strings
  • Improved consistency between humbuckers and single coils
  • Reduced need for scene switching
  • Better low-string articulation without high-string over-triggering
 
That's a great idea, and a useful request.
I have a bunch of G&L guitars, most of which have the PTB system, which gives you a bass cut knob in addition to the treble cut (regular tone) knob. Playing around with that bass cut has been educational- those bass strings carry a lot of signal when they vibrate, and cutting them out really changes the way that some effects behave. For example, cutting bass on the guitar totally changes the response of a fuzz, making it clean up because the bass strings aren't throwing that huge and hard to replicate signal as much, and anything using the envelope could benefit from this. Autowah or an envelope controlled filter would be the perfect application for this.
 
DLC86 said:
Isn't this what the emphasis control does (pretty much)?
Click to expand...
If I m not mistaken, the Filter Block's "Emphasis" control works Post-detection, not pre-detection...but I could be wrong! We need pre-detection control to equalize the EQ ... But I would defer to the Fractal God for any definitive answer!
 
Okay. Emphasis should work.

Just add, it may be good down the line to add separate (both)low and hi frequency controls for emphasis for super fine tuning is my next thought?

Does anyone know if the emphasis control we have now in Env Filter is a Tilt type into detector, Or just hi frequency detector?

Thanks for the correct info. I will keep tweaking.
 
austinbuddy said:
Okay. Emphasis should work.

Just add, it may be good down the line to add separate (both)low and hi frequency controls for emphasis for super fine tuning is my next thought?

Does anyone know if the emphasis control we have now in Env Filter is a Tilt type into detector, Or just hi frequency detector?

Thanks for the correct info. I will keep tweaking.
Click to expand...
I don't know but I guess it might be the same as the one in the compressor (you can see the frequency response graph there)
 
My 2 cents FWIW. With bass, using a split chain ( either via crossover block or hi-pass/lo-pass filters, x-over point +/-250Hz) and with the hi-pass path ONLY sent to the Envelope Filter (and Drives and other various effects), it's a whole different ballgame in terms of having less struggle getting the effect(s) to behave.

@austinbuddy I don't know if you've delved into this for bass tone creations, but for me it's made a world of difference.

Only downside, possibly, is that when only utlizing the hi-pass effected path, the dry lo-pass path is still audible, which may or may not be desirable if you want an effect on the entire broadband sound.
 
jimfist said:
My 2 cents FWIW. With bass, using a split chain ( either via crossover block or hi-pass/lo-pass filters, x-over point +/-250Hz) and with the hi-pass path ONLY sent to the Envelope Filter (and Drives and other various effects), it's a whole different ballgame in terms of having less struggle getting the effect(s) to behave.

@austinbuddy I don't know if you've delved into this for bass tone creations, but for me it's made a world of difference.

Only downside, possibly, is that when only utlizing the hi-pass effected path, the dry lo-pass path is still audible, which may or may not be desirable if you want an effect on the entire broadband sound.
Click to expand...
Yep, have struggled with it for bass application. have a Bootsy Collins one that is pretty good — but with the above and some better grasp of what parameters do with different inputs after experimenting from last few days, I can improve it further….I was making a Jerry Garcia type one and I could not get one Fliter channel to do both the low notes and high notes evenly, so made two channels. Will revisit with Emphasis tool again soon.
 
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