Adaptive Notch

Parameters

Width — Bandwidth of each notch in Hz, 1–200. Narrow widths (1–10 Hz) target a single tone surgically — useful for hum, whistles, or tuning resonances. Wider notches (50–200 Hz) catch a band rather than a tone — useful when the offending frequency drifts or smears. Same width applies to all active notches.

Depth — How deeply the notch attenuates the targeted frequency, in dB, −60 to 0. −40 to −60 dB is full surgical removal; −10 to −20 dB tames a resonance without making it disappear. Pair with a small width for clean removal of single tones, or a wider width with shallower depth for natural-feeling resonance control.

Speed — How quickly each notch tracks a moving frequency, 0.01–1. Slow tracking (0.01–0.2) handles slowly-drifting hums (mains hum, HVAC tones) without chasing harmless brief tones. Fast tracking (0.5–1) catches quickly-changing feedback or whistles in real-time, but can over-react to legitimate musical content. For static hum, use slow; for feedback hunting on live material, use fast.

Mix — Wet/dry blend, 0–100%. 100% is full notching; lower values blend the original signal back in for a more transparent effect. Useful when full notching removes too much body — bring the dry signal back to taste.

Gain — Output makeup gain in dB, −24 to +24. Notching usually reduces overall level slightly; this brings it back up.

Additional controls

Notches — Number of independent adaptive notches, 1–4. Each tracks its own frequency. Use 1 for a single hum or whistle; use 4 to chase multiple tones simultaneously (e.g. mains hum at 50 Hz with its harmonics at 100, 150, 200 Hz).

Detection Threshold (dB) — Minimum signal level (in dB) required for a candidate frequency to be tracked. Below this, the notch holds its current frequency rather than searching. Higher values prevent the notch from chasing quiet noise; lower values let it react to subtler tones.

Persistence — How long (in frames) a candidate frequency must remain detected before the notch locks onto it. Higher values prevent false locks on transient tones; lower values catch fast-emerging tones quickly.

Min Freq Hz / max Freq (Hz) — Lower and upper search bounds in Hz for adaptive frequency tracking. Constrains where the notch hunts. Set min above your bass content and max below the airy highs to focus the notch on the problematic mid-range. Essential for keeping the notch from grabbing onto musical content.

About Adaptive Notch

A regular notch filter sits at a fixed frequency. An adaptive notch finds the offending frequency on its own — it analyzes the spectrum, locks onto the strongest tonal component within the search range, and tracks it as it drifts. This is the right tool for: 50/60 Hz mains hum (which can drift in pitch with line voltage), feedback whistles in live recordings, and resonances that shift with the source. For surgical removal of fixed frequencies (like a known fan tone at 220 Hz), the Parametric EQ with a narrow Q-notch is more precise.

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