Every number in Loopex's MEQ_DEF table, where it came from, and how far it can be
trusted. Written so that a future change can tell a documented figure from a judgement
call without re-doing the research.
Read the tags strictly:
| Tag | Meaning |
|---|---|
| DOC | Manufacturer manual, service manual, spec sheet or patent |
| DOC-REISSUE | Manufacturer documentation, but for a modern reissue standing in for vintage hardware |
| MEASURED | Independent bench measurement or peer-reviewed analysis |
| COMM | Forum, blog, dealer copy, magazine editorial |
| CHOICE | Our decision. Not a fact. Never present it as one. |
| GAP | Not findable. Deliberately left unmodelled rather than estimated. |
Plugin-emulation marketing is not hardware documentation. Where a figure exists only in a plugin manual it is tagged COMM and named as such.
Char is the output machine — what the loops reach the world through. It is the last coloured stage before the converter:
… → PUNCH FX → Drift → Pump → [ gSat → LoCut → HiCut → CHARACTER → Glue → Out → Limit ] → dither → hardware
Input Tape is the complementary stage: media formats, printed into the loop at record time. Char is named machines, applied live at playback. Formats in, machines out.
loHz loDb · midHz midDb midQ · hiHz hiDb · sat · crushHz · makeupDb · grit · bits · clip · asym · compand · bwHz · poles · glueAtk glueRel glueKnee glueDist · limCeil · thrust
Notable ones: grit morphs the loop reader Hermite → linear → drop-sample. bwHz is the reconstruction-filter ceiling. poles sets LoCut/HiCut order. glueDist is distortion that rises with gain reduction. thrust is API's sidechain tilt.
Bypassed. master_character returns before touching anything.
Service manual supplied directly; the EQ was fitted by digitising the printed curve family at 600 dpi and least-squares fitting RBJ shelves against it.
- Response +0.5 / −1 dB; −3 dB at 4.5 Hz and 45 kHz; THD <0.03 % at +6 dBu; EIN ≤ −125 dBu — DOC (§1.7.2)
- Channel EQ is a Fächerentzerrer (fan equaliser). The published "20 Hz ±15 dB" and "20 kHz ±15 dB" are measurement frequencies — the gain reached at the edge of the band — not shelf corners. Reading them as corners is what made Bass and Treble inaudible for a year — DOC
- Fitted: low shelf 100 Hz S=0.64 (0.43 dB RMS), high shelf 4750 Hz S=0.50 (0.32 dB RMS) — MEASURED (our fit to their plot)
- Presence filter Q = 1, 150 Hz–7 kHz, ±11 dB — DOC
- Master limiter: ratio to 1:20, threshold +6 dBu, stereo LINK, PDM/VCA — DOC
- Voiced as near-nothing, because the desk is transparent by design.
The EQ Rupert Neve designed in 1985 for the Focusrite Studio Console at AIR Studios Montserrat — hence the name, and hence the nickname its top end still carries.
- Parametric bands 40–400 Hz and 600 Hz–6 kHz (×3 ranges) — DOC
- HPF 36/60/105/185/330 Hz and LPF 3.9/5.6/8.2/12/16 kHz, both 18 dB/oct — DOC
- THD 0.003 % line, 0.0008 % mic — DOC
- Transformer-coupled mic in, line in and output — DOC
- Shelf frequency points never published by Focusrite. Mix and SOS reviews give LF 33/56/95/160/270 and HF 3.3/4.7/6.8/10/15/18 kHz and disagree with each other — COMM. Our 95 Hz / 15 kHz carry that caveat.
- Correction: we first used 16 kHz for the HF shelf, having confused the unit's low-pass positions with its shelf.
- E vs G is a documented behavioural difference: E holds bandwidth constant with gain; G varies it (more boost/cut → more selectivity) — DOC (X-Rack manual)
- '242 vs '02: ±18 dB vs ±15 dB, 18 dB/oct HPF — DOC, though SSL's own documents conflict on shelf slope (6 vs 12 dB/oct)
- Original-console band ranges exist only in licensed plugin manuals — COMM
- G-series bus compressor: 3 ms / 0.3 s / 4:1 — DOC
- No original-console THD or transformer data exists anywhere — GAP
- LF shelf 35/60/110/220 Hz ±16 dB; mid bell 360/700/1.6k/3.2k/4.8k/7.2 kHz ±18 dB; HF shelf fixed 12 kHz ±16 dB; HPF 50/80/160/300 Hz, 18 dB/oct — DOC
- THD ≤0.07 % at +20 dBu — DOC
- Third-harmonic dominant, bench-measured — MEASURED (Sound On Sound, 1073N)
- Mid-band Q: AMS Neve state only "fixed Q". No number exists — GAP
- Dynamics from the 33609 (the 2254 diode bridge as a stereo bus box): comp attack 3/6 ms, release 100–1500 ms plus Auto1 100 ms/2 s and Auto2 50 ms/5 s, ratio 1.5–6:1, soft knee reaching full ratio ~6 dB above threshold — DOC-REISSUE
- THD per mode: <0.075 % bypassed, <0.2 % compressing, <0.45 % limiting — DOC.
The only unit in this entire table whose maker publishes distortion under gain
reduction, and the sole basis for
glueDist.
Trap: a "0.3 % THD at 6 dB GR, third-harmonic dominant" figure circulates near 2254 discussions. It is from an SOS review of the Rupert Neve Designs 5254, a different modern unit. Do not apply it here.
Weakest-documented row in the table. Treat every figure with suspicion.
- LF shelf 50/80/100/150 Hz; low-mid 250/500/1k/2k; high-mid 3k/5k/7k/9k; HF shelf 8k/10k/12k/15k; ±15 dB; Q 1.3 — DOC for the reissue; Trident's own handbook for the original console prints no dB range and no Q
- The two sources disagree on the lowest LF point (50 vs 80 Hz)
- Transformer-coupled in and out; inductor mid bands — DOC
- Harmonic order: GAP. Do not assume 2nd or 3rd. Our asym is a CHOICE.
- Dynamics from the CB9146 (FET): attack 20 µs–200 ms, release 25–500 ms, ratio to 20:1 — COMM only, and specifically a forum user reading a photograph of a front panel. No manufacturer documentation for this unit exists.
- Correction: the CB9066 is an equaliser, not a compressor. That pairing was wrong.
Distinct from the 962 desk. Different machine, different character.
- 60 Hz–18 kHz ±1 dB at 15 ips; 60 Hz–20 kHz at 30 ips — DOC
- W&F 0.04 % DIN peak weighted; operating level 510 nWb/m; bias 240 kHz — DOC
- THD specified explicitly as 3rd harmonic, 1 % max at operating level. Studer publish no even-order figure at all — DOC
- Head bump: not documented by Studer. The word does not appear in 1.1 MB of service text — GAP. Our ~60 Hz comes from Jack Endino's measured A80 MkII and A827 siblings (+1 to +1.8 dB, 30–62 Hz at 15 ips) — MEASURED, third party
- The structurally useful law: the bump is a damped ripple, not one peak, and it shifts one octave up per speed doubling — MEASURED
- LF 30/40/50/100/200/300/400 Hz; MF 200/400/600/800/1500/3000/5000; HF 2500/5000/7000/10k/12.5k/15k/20k; ±12 dB stepped; 12 dB/oct — DOC
- Proportional Q published only as a graph. The two community figures disagree by ~2× — GAP, deliberately not modelled
- Correction: we first used 900 Hz and 6 kHz. Neither is on either switch.
- Dynamics from the 2500: attack .03/.1/.3/1/3/10/30 ms; release .05–2 s plus variable 50 ms–3 s, no auto; ratio 1.5–∞; HARD/MED/SOFT knee; TYPE OLD = feed-back, NEW = feed-forward; THAT 2180 VCAs with a 2252 RMS detector — DOC
- THRUST (US Patent 5,170,437): a sidechain filter before the RMS detector, +10 dB/decade, −15 dB at 20 Hz to +15 dB at 20 kHz, pivot ≈ 632 Hz, inverse of the pink-noise curve. Bass therefore stops driving the gain reduction — DOC, with a plotted curve in API's manual and a five-stage RC ladder in the patent. We implement a first-order tilt, an approximation of that ladder.
- Max output +32 dB, response ±0.5 dB 20 Hz–50 kHz, S/N 120 dB, clips +28 dBu — DOC
- Knee width in dB: GAP. API's HARD/MED/SOFT plot has no scale on either axis and nobody has measured it. Ours is a CHOICE.
- THD under gain reduction of the 2500 as built: GAP. No measurement exists publicly.
But the THAT 2180 VCA inside it (four per channel, per SOS's inspection) publishes
plots — DOC, component-level, not whole-unit:
- 0.005–0.010 % at unity gain → 0.020–0.030 % at ±15 dB gain. Distortion triples to quadruples once the VCA actually pulls gain.
- Datasheet FFT (Fig. 13): 2nd harmonic −80.1 dB, 3rd −104 dB — strongly even-order dominated, third some 24 dB below.
- Second mechanism THAT document: 2252 ripple modulating the VCA, worst at low
frequencies under heavy GR. Their alignment nulls it at 100 Hz / ~20 dB compression.
So API carries a small even-order grit (−0.05) against the Neve's larger odd-order
0.35. In
MEQ_DEFthe sign ofglueDistcarries harmonic order, the magnitude carries amount. The 2510/2520 op-amps and the output transformer remain GAP.
- Caveat on the pairing itself: 550A is 1967, 2500 is 2000s. This is matched by function — the API bus compressor people actually use — not by era, unlike Neve→33609 or ISA 110→ISA 130 which are genuine contemporaries.
- ±0.75 dB 200 Hz–20 kHz at 30 ips; ±2 dB 35 Hz–28 kHz. At 15 ips, ±0.75 dB 100 Hz–15 kHz, ±2 dB 20 Hz–20 kHz — DOC (Table 1-4)
- 3rd harmonic <0.3 % at 370 nWb/m, <3.0 % at 1040 nWb/m (+9 VU). Even-order <0.1 % at reference — DOC. That 1:3 ratio is what sets its asym, and the 0.3 → 3 % progression over +9 dB is why it has the lowest Limit ceiling.
- W&F ±0.03 % peak weighted; bias 432 kHz — DOC
- HF −3 dB point: GAP — Ampex publish only ±0.75 and ±2 dB windows
- Head bump: GAP, same as the A800. Ampex's spec structure implies a bound of ≤±2 dB below 200 Hz, but that is an inference from the table's shape, not a figure.
- Ampex never made a compressor or limiter. Catalogue OCR-searched; two circulating listings ("Ampex 350 + Triad opto", "AM-10 with Fairchild") are third-party racks.
- 40 kHz fixed; response 20 Hz–18 kHz; "12 bit sample resolution, special non-linear format, reduced noise"; tuning +½/−1 octave — DOC (service manual §I)
- 16-bit ADC and DAC with companded 12-bit storage — DOC (operator's manual)
- The companding law is never named. "Special non-linear format" is a deliberate non-disclosure, not an omission — GAP. µ-law (µ=255) is our CHOICE: period- correct and behaves as described.
- It has a real reconstruction filter, unlike the E-mus. Its character is the
companding quantiser, not imaging — hence low
gritandbwHz = 18000. - Service manual parts list uses internal Akai part numbers (
EF-…), so filter component values are not derivable from it — GAP
- Sample rate 7.5–48 kHz; bandwidth 3–19.2 kHz — DOC
fc = fs × 0.4, annotated on the voice block diagram. Rate and bandwidth are locked at 2.5:1 — DOC- 6-pole, 36 dB/oct MF6CN-50 switched-capacitor filter on both record and playback (IC7 + IC109 ×8), plus a fixed 2-pole 18 kHz stage — DOC
- 12-bit linear. No companding — DOC. Do not port the MPC60 assumption across.
- Pitch by variable sample clock — no interpolation, no drop-sample — DOC
- Frequency response, S/N, THD: never published by Akai — GAP
- Correction: independently adjustable bandwidth vs sample rate is a feature of Inphonik's RX950 plugin, not the hardware. We recommended this unit on a feature it does not have.
- 26.04 kHz fixed (shared with the Drumulator and SP-12); 12-bit linear, no companding — DOC
- No reconstruction filter. Output is bare zero-order hold; the imaging is the sound — DOC
- Drop-sample pitch shifting: fractional index, truncated, no interpolation. Pitching down repeats samples outright — MEASURED (Yeh, Nolting & Smith, CCRMA/ICMC 2007)
- No dedicated audio ADC — a 12-bit SAR loop around the playback DAC (AD7541) — DOC
- Output channel filters: ch 1–2 dynamic SSM2044, ch 3–6 fixed, ch 7–8 unfiltered — DOC
- Exact fixed-filter cutoffs: GAP
The archive.org SP-1200 service manual scan is image-only; an early automated fetch returned confident "quotes" that were actually SP-12 text. Treat any online claim of quoting it with suspicion.
- Same 26.04 kHz clock, same 12-bit linear format, same absence of a reconstruction filter as the SP-1200. The published "27.5 kHz" is a spec-sheet error; measured at 26 kHz — MEASURED (CCRMA)
- Differentiated from the SP-1200 by its darker fixed output filters, which is what
our
hiHz/hiDbcarries - Anti-alias filter measured as needing an order-11 digital fit, attenuating above ~15 kHz — MEASURED
- The manual's "42 dB per octave" is in a generic tutorial sentence — it is not a spec for this unit and is commonly misquoted
- SSM2044 self-oscillation trim 1.3 kHz — DOC
Most of these consoles have no compressor. Each voicing borrows the unit the same maker built in the same era, rather than being given invented timings.
| Voicing | Unit | Topology | Pairing |
|---|---|---|---|
| Neve | 33609 | diode bridge | Solid — only source publishing THD under GR |
| Air | ISA 130 | VCA | Solid — same ISA rack, full spec table |
| SSL | G-series bus comp | VCA | Solid |
| 962 | its own desk limiter | PDM/VCA | Solid — in-unit |
| API | 2500 | VCA + RMS | By function, not era |
| Trident | CB9146 | FET | Weak — zero manufacturer documentation |
| Studer, Ampex | none exists | — | class-appropriate timings |
| all four samplers | none exists | — | neutral Glue, hard rail on Limit |
- "Transformers and tape mean even harmonics" is false. Contradicted three times
independently: SOS measured the Neve 1073 third-harmonic dominant; Studer specify the
A800's THD as 3rd and publish no even-order figure; Ampex document the ATR-102 at
<0.3 % 3rd against <0.1 % even-order. The
asymcolumn was built on folklore and is no longer used as a differentiator. - "Juno chorus-console" was not a real machine — and the voicing contained no chorus.
- The S950's independent bandwidth control is a plugin feature, not Akai's.
- CB9066 is an EQ, not a compressor.
- Crush-rate corrections were sonically inert.
eqCrushis an integer hold count, so MPC60 never crushed at 30 kHz or 40 kHz, and 22 kHz and 26.04 kHz both give ÷2. - Nobody publishes harmonic order behind a THD figure — Neve's 33609 excepted.
Head bump for both tape machines · Neve mid Q · MPC60 companding law · API knee width · API 2500 THD under GR · S950 frequency response and THD · SP-1200 fixed filter cutoffs · Trident's entire spec · harmonic order for every unit except the Neve.
Studer 961/962 service manual (supplied) · Studer A800 service notes · Ampex ATR-100 manual · MRL equalization fundamentals · Jack Endino, measured recorder curves · AMS Neve 1073 · AMS Neve 33609 · SOS Neve 1073N · Focusrite ISA110 manual · Focusrite ISA 130/131 · SSL X-Rack EQ · SSL Origin · API 550A · API 2500 manual, THRUST + knee plots · US Patent 5,170,437 · THAT 2252 datasheet · Trident A-Range handbook · Akai MPC60 service manual · Akai S950 operator's manual · E-mu SP-12 service manual · Yeh, Nolting & Smith, SP-12 modelling, CCRMA 2007