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Upward compression effect

Upward Compression Effect

Thinking about different pedal ideas. I recently stumbled upon some sort of precision pedal that would have the filters (focus) sweepable to find the sweet spot, and then an upward compression on the resonant peaks to give extra punch and attack. So basically we could zero in on the body of the guitar pick attack and the pick attack and then have an upward compression to add dynamic punch. This is a sophisticated concept. We’re essentially describing a Dynamic Resonant Processor. By combining sweepable "Search" filters with upward compression, we’re moving away from a standard "set-and-forget" EQ and into the realm of active frequency-dependent transients.[^1]

1. The "Focus" Stage: Sweepable Filters

To "zero in" on the pick attack or the body, you'll need high-\(Q\) (narrow bandwidth) filters.

  • The "Search" Mode: You’ll want a parametric filter where you can sweep the frequency (\(f_c\)) to find the resonant "honk" of the guitar body (usually 400Hz–800Hz) or the "click" of the pick (2kHz–4kHz).
  • The Sweet Spot: Once found, the "Focus" control narrows the \(Q\) so the compressor only "sees" that specific frequency range.

2. The "Punch" Stage: Upward Compression

Standard downward compression squashes peaks above a threshold. Upward compression does the opposite: it boosts signals below a threshold, or in your case, it "pushes" the resonant peak higher when it's detected.

  • Why it works for Pick Attack: A pick attack is a very fast, high-amplitude transient. By applying upward gain specifically to that peak, you’re not just making the guitar louder; you’re making the initial hit feel more explosive.
  • The "Precision" Element: Because it's frequency-selective, you won't get the "pumping" effect of a full-band compressor. The low strings stay steady while the "click" of your pick gets an extra \(6\text{dB}\) of "shove."

3. Implementation Ideas for your "Bloodhoney" Project

Since you’re already using the Daisy Seed (STM32), you have the DSP horsepower to do this in the digital domain, which is much easier than doing it with analog op-amps.

  • The Filter: Implement a Biquad Filter in C++ or JAX. You can make the frequency and \(Q\) controllable via external potentiometers.
  • The Detector: Use an Envelope Follower specifically on the output of that filter.
  • The Logic: If the envelope of the "Focus" band exceeds a certain level, apply a dynamic gain multiplier to that band before mixing it back with the dry signal.
\[Output = \text{Dry} + (\text{Focused_Signal} \times \text{Dynamic_Gain})\]

4. Why This is Novel

Most "attack" pedals (like the Boss Slow Gear or various compressors) look at the entire signal. Your idea is a Surgical Transient Shaper.

Wit's End: It's essentially a "magnifying glass" for your guitar tone—it finds the bit you like and puts a spotlight on it. It’s like a Bayesian update where you’ve found high-density evidence of a "good note" and decided to weight it more heavily in the final mix.

A Potential Challenge

The "ringing" of a high-\(Q\) filter can sometimes smear the transient you're trying to sharpen. You might need to look into Finite Impulse Response (FIR) filters or specific Phase-Linear designs in your DSP code to keep that pick attack feeling "immediate" and not "blurry."

[^1]: In the context of my Bayesian Data Science background, you can think of the "Focus" filters as defining the Region of Interest, and the upward compression as a way to increase the Signal-to-Noise Ratio of the specific "pick attack" events I want to highlight.