mbp15-1-audio-dsp/mb-compressor-params.md

LSP mb_compressor_stereo — parameter reference

Every key in the multiband_compressor node of graph.json, with the LSP port name in bold and the JSON symbol in code. Values shown are the ones currently in the graph (8-band split, split-limiting branch).

Source of truth: mb_compressor_stereo.ttl from lsp-plugins 25.08.

Global (once, not per band)

Key	LSP name	Value	Meaning
enabled	Enabled	1	plugin active
mode	Compressor mode	1 = Modern	band-split topology. 0 Classic = analog-style tree of crossovers; 1 Modern = flat per-band summation (cleaner, used here); 2 Linear Phase = FIR, high latency
g_in / g_out	Input / Output gain	1.0 / 1.4	linear. g_out 1.4 ≈ +3 dB — where the EQ's g_in 0.5 pad is restored, after the band detectors
g_dry / g_wet	Dry / Wet gain	0.0001 / 1.0	parallel mix — effectively 100 % wet

Crossover (index 1–7)

Key	LSP name	Meaning
cbe_N	Compression band enable N	turns split point N on → creates that band boundary. All 7 = 1 → 8 bands
sf_N	Split frequency N (Hz)	the crossover frequency. Currently 60 / 80 / 100 / 130 / 160 / 200 / 500

Per band (index 0–7)

Key	LSP name	Units	Meaning
ce_N	Compressor enable N	toggle	band compresses (0 = passes flat)
al_N	Attack threshold N	linear gain (0.001–1.0)	the threshold — level above this is compressed. dB = 20·log₁₀(g); 0.093 ≈ −21 dB
at_N	Attack time N	ms	how fast gain reduction engages once over threshold
rt_N	Release time N	ms	how fast gain recovers once back under threshold
cr_N	Ratio N	x:1 (1–100)	dB in per dB out above threshold. 1 = off, 2 = gentle, 50 ≈ brick-wall limiter
kn_N	Knee N	linear gain (0.063–1.0)	width of the soft transition around the threshold. 1.0 = hard corner; lower = wider / softer (0.063 ≈ ±24 dB — ratio ramps in over a huge range). Plugin default 0.5 (−6 dB)
mk_N	Makeup gain N	linear (0.001–1000)	post-compression level trim for the band. 1.5 ≈ +3.5 dB, 2.0 = +6 dB
scm_N	Sidechain mode N	enum	detector: 0 = Peak, 1 RMS, 2 LPF, 3 SMA. Peak is used on every band (right for limiting; plugin default is RMS)
bth_N	Boost threshold N	linear gain (1e-6–1e-3)	only used when band compression mode = Up / Boost. Inert here — see note below
bsa_N	Boost signal amount N	linear gain (2.5e-4–3981)	ditto — inert

Other per-band ports exist in the plugin but are left at default and not written to the graph: cm_N (compression mode: Down/Up/Boost — default Down), bs_N/bm_N (band solo/mute), rrl_N/rl_N (release threshold/level — 0 = track the attack threshold), and the sc*_N sidechain family (sce_/scs_/sscs_/sla_/scr_/scp_/sclc_…).

Current bands, in plain English

Band	Range	al (thr)	at / rt	cr	kn	mk	reads as
0	< 60 Hz	0.093 (−21 dB)	2 / 120 ms	50	0.10 (−20 dB)	1.5 (+3.5 dB)	fast brick-wall; near-empty behind the 60 Hz EQ high-pass
1	60–80 Hz	0.078 (−22 dB)	5 / 120 ms	50	0.06 (−24 dB, clamped)	1.5 (+3.5 dB)	lowest ceiling, 50:1, softest knee → heavy but gradual
2	80–100 Hz	0.095 (−20 dB)	6 / 130 ms	30	0.12 (−18 dB)	1.7 (+4.6 dB)	one notch gentler than band 1
3	100–130 Hz	0.120 (−18 dB)	8 / 150 ms	20	0.20 (−14 dB)	2.0 (+6 dB)	old "90–200" midbass character
4	130–160 Hz	0.130 (−18 dB)	8 / 150 ms	18	0.24 (−12 dB)	2.0 (+6 dB)	"
5	160–200 Hz	0.140 (−17 dB)	9 / 150 ms	16	0.28 (−11 dB)	2.0 (+6 dB)	eases toward the body band
6	200–500 Hz	0.159 (−16 dB)	10 / 150 ms	15	0.30 (−10 dB)	2.0 (+6 dB)	low-mid body (snare / male vocal)
7	500 Hz+	0.284 (−11 dB)	8 / 150 ms	5	0.40 (−8 dB)	1.3 (+2.3 dB)	single gentle catch-all above 500 Hz

Notes / gotchas

• Knee direction. Lower kn = wider / softer knee, not harder. kn_1 = 0.06 on the 60–80 Hz band is the softest the plugin allows (it clamps 0.06 → 0.063). That band still pulls peaks down hard because of the low threshold

  • 50:1 ratio; the wide knee just means the ratio ramps in gradually starting well below −22 dB (so there is some low-level gain reduction too). To clamp those octaves only near the ceiling and keep them cleaner below it, raise kn_1 / kn_2 toward 0.3–0.5.

• bth_N / bsa_N are dead config. Set to 1.0 in the graph (inherited from upstream) but their valid ranges are ~1e-6–1e-3 and 2.5e-4–3981 — the host clamps them. They only apply to upward / boost compression, which is not enabled (cm_N is never set, so every band is downward), so it is harmless.

• al_N is linear, not dB. Same for kn_N, mk_N, g_*. Convert with dB = 20·log₁₀(value).