HF Cymbal / Shimmer Repair

If you've run MiniMax Music 3 through FlashSR and thought "why do my cymbals sound like they're underwater," this is the node you were looking for. Bandwidth extension reconstructs high-frequency content, and sometimes what it reconstructs is a smeared, diffuse shimmer that sits on top of every hi-hat and ride. HF Cymbal / Shimmer Repair dynamically shapes only the high-frequency band - it tames sustained, non-transient HF energy while protecting the attack of each hit. Your low/mid band is never touched.

It works on the same principle as a de-esser, but for the whole top end instead of just sibilance: separate a fast envelope and a slow envelope of the HF energy, and attenuate the slow, sustained component that represents tails, reverb and artificial shimmer. When the fast envelope clearly exceeds the slow one, that's a transient - a real cymbal attack - and it gets protected instead of ducked.

Where it sits

Stage 4, right after the FlashSR Hybrid Crossover and before the POST low-pass. Feed it the hybrid output, not the raw MiniMax audio. In the pack's chain it's the last line of defense against FlashSR artifacts before you move on to mastering.

The modes

The mode dropdown gives you a ladder, and the defaults are the right call:

• Gentle (default) - conservative, batch-safe cleanup.
• Cymbal clarity - suppresses smeared sustain more strongly, still protecting attacks.
• Reverb / shimmer control - the heavy one, for diffuse artificial HF tails.
• Custom - uses your exact parameter values.
• Bypass - pass-through, useful for A/B.

Start at Gentle. The tooltip and the README both push the same message: escalate only on material that actually needs it.

Inputs that matter

The important knobs once you leave the presets behind:

• start_frequency_hz (default 8000) - the band above which it works. Lower = more presence/upper harmonics affected; too low dulls instruments and vocals.
• sustain_reduction_db - how much attenuation the sustained HF energy can take.
• fast_envelope_ms / slow_envelope_ms - the attack vs. sustain time constants that separate transients from tails.
• transient_sensitivity - how different the fast and slow envelopes must be before HF energy counts as a transient and gets protected.
• side_hf_reduction_db - the genuinely clever one. It statically reduces the stereo Side channel's HF (M/S processing), which narrows artificial reverb/shimmer when it's excessively wide without touching the mono image.
• mix - parallel wet/dry blend for when a preset is slightly too strong.

Outputs are audio, hf_repair_json (preset, effective parameters, measured processing stats), and info. The JSON plugs into MiniMax Song Metadata.

Installing it

Pack install via ComfyUI Manager (search "MiniMax Music Production Toolkit") or:

cd ComfyUI/custom_nodes
git clone https://github.com/jplenio/ComfyUI-MiniMax-Music-Production-Toolkit.git
cd ComfyUI-MiniMax-Music-Production-Toolkit
python -m pip install -r requirements.txt

Dependencies: scipy, soundfile, imageio-ffmpeg, mutagen, Pillow. Restart ComfyUI and hard-refresh once.

Gotchas

This node reduces artifacts; it doesn't eliminate them. The README is explicit that hybrid mixing + HF repair are meant to reduce, not remove, FlashSR's inventions. If cymbals still sound watery after Gentle, the troubleshooting checklist says to work upstream first - lighter PRE filter, Original SRC only A/B, lower flashsr_hf_mix - before reaching for stronger repair here. And watch start_frequency_hz: pushed too low, you're now shaping vocal presence and instrument harmonics, which is a different (and riskier) surgery than the one the node is named for.