draft: true
Name: ESP
short-description: A MS-20-style External Signal Processor that includes a preamp, bandpass filter, envelope follower, gate, and 1v/oct pitch outs.
Language: C++ (Pico SDK + ComputerCard)
Creator: Ben Regnier
Version: 1.0
Status: Released
date-created: 2025-12-01
date-updated: 2026-02-09

tags:
  - external-signal-processor
  - envelope-follower
  - pitch-tracker
  - gate-extractor
  - filter

summary: |
  ESP processes incoming audio through a gain stage and bandpass section, then derives envelope, gate, trigger, and pitch control signals.
  Main controls preamp gain, X sets lower cutoff, and Y sets upper cutoff.
  In switch middle, pitch updates are held unless gate is high; otherwise pitch tracks continuously.
  Audio Out 1 is post-gain signal and Audio Out 2 is bandpassed output.

panel:
  inputs:
    - id: AudioIn1
      name: Audio Input
      description: Source signal for all ESP analysis/processing stages
  outputs:
    - id: AudioOut1
      name: Post-Gain Monitor
      description: Preamped signal after soft clipping
    - id: AudioOut2
      name: Bandpass Monitor
      description: Band-passed signal used by envelope and pitch detector
    - id: CVOut1
      name: Pitch CV (1V/Oct)
      description: Pitch estimate converted to calibrated 1V/oct-style output # certainty: medium (algorithmic approximation in code)
    - id: CVOut2
      name: Envelope CV
      description: Envelope follower output derived from bandpassed signal
    - id: PulseOut1
      name: Gate Out
      description: Schmitt gate derived from envelope thresholding
    - id: PulseOut2
      name: Trigger Out
      description: Short trigger on gate rising edge

controls:
  knobs:
    - when: { z: up }
      main:
        name: Preamp Gain
        description: Exponential gain from low boost to high drive
      x:
        name: Bandpass Low Cut
        description: Lower cutoff index for high-pass stage
      y:
        name: Bandpass High Cut
        description: Upper cutoff index for low-pass stage
    - when: { z: middle }
      main:
        name: Pitch Hold Mode
        description: Pitch updates only while gate is active; helps stabilize tracking
  leds:
    - when: { mode: activity }
      display: list
      items:
        - id: LED0
          name: Bandpass Activity
          description: Brightness follows bandpassed signal level
        - id: LED2
          name: Pitch CV Level
          description: Brightness follows pitch CV output level
        - id: LED3
          name: Envelope Level
          description: Brightness follows envelope CV output level
        - id: LED4
          name: Gate State
          description: Lit while gate output is high