HQ 1 · Stereo Cleanup

If you've listened to a few AI-generated songs and something felt cheap without you being able to name it, it was probably the top end. AI renders put a lot of energy up high, and they spread it wide - a hissy, unstable stereo fringe that real recordings don't have. HQ 1 · Stereo Cleanup exists to clean exactly that, and it's the one Audio HQ stage that's on by default in every Plenio template. That's not an accident: it's the cheapest quality win in the pack.

The trick: leave the middle alone

Most de-hiss tools treat both channels equally and end up dulling the vocal. This one works in mid/side instead. It splits the song into the mid (what both channels share - voice, kick, snare, bass) and the side (the difference - width, room, and that shimmer at the edge), then only touches the side. The mid is never filtered, which is why you can run it on a finished master and still recognise the singer.

Three things happen to the side. A zero-phase high-cut above a chosen frequency, blended in by how hard you've set the cleanup. A spectral cleanup above 2 kHz, where the side is no louder than its diffuse surroundings, turned down smoothly by up to 12 dB. And a little warmth: 2x oversampled, slightly asymmetric saturation above 400 Hz that adds 2nd and 3rd harmonics. At the stock setting that's density, not distortion - the 3rd harmonic of a -6 dBFS tone sits around 53 dB down.

Inputs and outputs

You set audio - the song, every item of a batch processed - and preset. The preset list is the same five choices across all three HQ stages: auto, standard, gentle, strong, wide, plus custom.

• auto reads the genre off brief and picks a profile; no brief, and it falls back to standard.
• standard (pop, hip-hop, soul, world): side high-cut 10.5 kHz, cleanup 65%, warmth 0.18.
• gentle (classical, jazz, folk): 11.5 kHz, 55%, 0.14.
• strong (rock, metal, punk): 9.5 kHz, 80%, 0.25.
• wide (electronic, dance, ambient): 14 kHz, 40%, 0.12.
• custom opens the three numbers behind whichever profile you had, so you can dial between them.

brief is the optional one: Song Brief or Cover Brief, and its genre is all that's read. If you're running the node standalone, leave it off and use auto or pick a profile by hand.

Outputs are audio - the cleaned song, same sample rate, same length, not normalised - and report, a Plenio report carrying profile, settings and how much the side moved above 10.5 kHz. The report wires into Export Release's record input, so the choice ends up documented in the .plenio.json, which is the kind of thing you appreciate three weeks later.

What it measures out to

Across nine YuE2 takes, the audible band barely moves: ±0.4 dB below 6 kHz. The side above 10.5 kHz drops 10 to 13 dB. That's the whole pitch - the music untouched, the shimmer gone.

Which means one honest caveat: this narrows your stereo image on purpose. If you're making ambient or electronic music where wide airy highs are the aesthetic, wide keeps far more of the side (14 kHz cut, 40% cleanup), and the manual will tell you those non-standard profiles are provisional - reasoned starting points, not listening-tested ones. The summary line on the node literally says so.

Installing it

You get it with the pack, so there's nothing node-specific to fetch:

cd ComfyUI/custom_nodes
git clone https://github.com/jplenio/Plenio-Music-Production-System

Or search Plenio Music Production System in Manager. Restart, then run template 0 · System Check to confirm your install. No Python packages, no model files, no VRAM - this stage is pure DSP and runs on the CPU in a few seconds per minute of music. In the templates it lives inside the Plenio · Master block (open it with the icon at the top right of the node); in 4 · Enhance & Master it's a plain node on the canvas.

Where people get burned

Two things trip people up. First, a mono input gets the warmth only - no side signal exists, so there's nothing to clean. Second, if the song already sounds dull before it gets here, this will make it duller, and stacking HQ 3 · De-Reverb on top makes it duller still. Clean the shimmer; don't sterilise the song.