The mud between the notes.

Why a chord collapses into sludge the moment you drive it — and the old, measurable fix most saturators ignore.

Every producer has felt it. A single note takes saturation like a gift — it gets fat, rich, alive. Stack that note into a chord, push the same drive, and it turns to mud. People blame their monitors, their ears, the preset. It isn't any of those. It's a property of the math, it has a name, and it can be measured. So we measured it.

What actually happens

Any saturator is a nonlinearity: it bends the waveform to add harmonics. Feed it one tone and the new content lands on that tone's own harmonics — octaves, fifths — frequencies that are musically related to the input, so the ear hears "richer," not "wrong."

Feed it two or more tones at once and something else happens. A nonlinearity also produces the sums and differences of every input frequency: f1+f2, f1−f2, 2f1−f2, and so on. These products are not harmonically related to the notes you played. This is intermodulation distortion (IMD), and it is the standard way labs characterise a nonlinear system precisely because it exposes the non-musical content harmonic-distortion tests hide.

A dense chord is many simultaneous tones. The number of intermodulation products grows fast with the number of tones — so the denser and more harmonically rich the chord, the more non-musical energy piles up in the gaps between the notes. That energy is the mud.

The measurement

We ran a Cm9 chord (C, E♭, G, B♭, D) as pure sine tones through a saturator, loudness-matched input to output so level wasn't doing the talking. We then measured the share of output energy sitting on frequencies that are neither the played notes nor their harmonics — literally, the stuff you didn't play. We call it the junk fraction.

Pure sines are deliberate: with no harmonics in the input, every frequency the saturator adds is unambiguously either a harmonic or junk, so the IMD is isolated cleanly. Real instruments carry their own harmonics, so the absolute junk fraction on a finished track sits lower — but the wideband-vs-multiband gap is the same, and that's what the clips below let you hear.

Then we repeated it while changing only one thing: how many frequency bands the signal is split into before saturating. One band = an ordinary wideband saturator — here that's our own engine set to 1 band, the fairest baseline there is (identical curve, no hand-picked weak competitor). The signal is split, each band is saturated alone, and the bands are summed back.

The result

An ordinary wideband saturator put ~30% of its output energy on inharmonic frequencies — neither the notes nor their harmonics, so not the musical saturation you wanted (and ~47% when pushed hard). Split the same signal into 48 bands first and that collapses to ~1% — same chord, same drive, same loudness. Fewer notes share each band, so far fewer intermodulation products are generated in the first place.

This isn't a new trick. Adding distortion to signals before summing them — rather than to the summed mix — is long known to sound consonant and free of intermodulation. The contribution here is simply doing it densely, and showing the curve.

Hear it

Every clip below is rendered straight from the engine and loudness-matched, so you're judging the sound, not the level. Hit play; where a clip has two sources, switch between them mid-playback to A/B the exact same moment.

Test conditions: one Cm9 chord, the same engine, same algorithm, loudness-matched to −16 LUFS. CLARITY is the band count — at the bottom it's 1 band (a normal wideband saturator; we call it "ordinary"), at the top it's 48 bands (NOVA). Unless a clip says otherwise, that band count is the only thing changing.

CLARITY is the band count. Turn it up and the held chord morphs from an ordinary 1-band saturator (gritty, muddy) to NOVA's 48 bands (clean) — one knob, 0 → 100%, then held clean so you hear the result:

"But isn't that just less saturation?" Fair question. Here the ordinary 1-band saturator is turned down until it adds the same harmonic warmth as NOVA-48 — matched saturation, not matched drive. It's still ~15× muddier (~23% junk vs ~1.5%). Switch between them:

And because the mud never piles up, you can push far past where a wideband saturator collapses. Both cranked to 200% drive: ORDINARY turns to pure sludge; NOVA-48 just gets richer and denser and stays a chord:

Why it matters for you

If you saturate tonal material — chords, lead stacks, pads, reese basses with intervals — band count is the difference between "driven and clear" and "driven and muddy." On a single note or a kick it barely matters. On a maj7 pad it's everything. Drive as hard as the track wants; just split first.

Aliasing — and we don't hide it

Any nonlinearity also generates harmonics above the audio band. At a standard sample rate those fold back down as inharmonic alias tones — the brittle, "digital" edge cheap distortion has. NOVA oversamples in HQ mode to push them out of the way. Below is FOLD driven hard, at 1× and in HQ: at 1× it aliases, and we're showing it rather than hiding it.

What it costs

Processing headroom — how many times faster than real time the engine runs on a single core, offline:

Single-threaded, offline, on this build's reference machine. Live DAW CPU depends on your buffer size and host — treat this as relative headroom, not an absolute percentage.

Sources

1. Intermodulation distortion — definition (sum/difference tones): Wikipedia
2. IMD as the lab measure of nonlinearity: Klippel
3. IMD in music / why it muddies a mix: Production Expert
4. Distort-before-sum stays consonant: Elliott Sound Products

Method note: junk fraction = output energy outside ±8 Hz of any played note or its harmonics, Hann-windowed FFT, loudness-matched. Measured on our own engine; figures will be republished with the full dataset.