Humble Audio — Quad Operator Algo Extension

• Manual PDF

Manual PDF

Humble Audio Quad Operator Cheat Sheet

What it is

A 4-operator digital linear FM oscillator/LFO bank with: - 4 independently usable operators - continuously variable waveshape per operator: sine → triangle → square → saw - full modulation matrix: each operator can modulate any operator, including itself - AR FM external audio-rate mod input with its own modulation sends - optional Algo expander for saving/crossfading FM routing setups

Quick-start patch

For classic, harmonic FM: 1. Set VCO/LFO to VCO 2. Put all 4 operators in LOCK 3. Set all Detune knobs to 12 o’clock 4. Set all Shape knobs fully CCW (sine) 5. Turn all Mod 1–4 knobs fully CCW 6. Patch 1V/Oct and take audio from one or more Op outputs 7. Raise one operator’s Mod send into another operator 8. Use the modulating operator’s Gain CV/level to animate FM depth

Core concept

Each row = one operator.

Each operator has: - a tuning control (Ratio in LOCK, coarse tuning in FREE) - Detune - Shape - Gain - four Mod sends to Operators 1–4

LOCK vs FREE

LOCK - Operator follows master pitch at an integer ratio - Best for classic harmonic FM - Ratio knob selects 1/11 to 11x relative to master tuning, in integer steps

FREE - Operator becomes an independent oscillator/LFO - Ratio knob becomes the operator’s own coarse tuning - Ratio CV becomes 1V/oct for that operator - Better for independent oscillators / inharmonic FM

Master controls

Coarse knob

• Master tuning for all operators in LOCK
• Exponential response across 8 octaves
• Range:
• VCO mode: 16.35 Hz (C0) to 2093 Hz (C7)
• LFO mode: 0.511 Hz (C-5) to 65.41 Hz (C2)

Fine knob

• Master fine tune for all locked operators
• Range: ±6 semitones

VCO / LFO toggle

• Changes base frequency range of the whole module

1V / Oct input

• Master pitch CV for all operators in LOCK
• Voltage range: -1V to +5V
• Normal: 0V
• Sample rate: 6 kHz

LF FM input

• Low-frequency pitch modulation input for all locked operators
• Good for vibrato, bends, pitch envelopes
• Voltage range: -5V to +5V
• Normal: 0V
• Sample rate: 6 kHz

AR FM input

• External audio-rate modulation input
• Lets external audio modulate internal operators
• Especially useful for feedback/complex FM patches
• Voltage range: trimmable for -5V to +5V or -10V to +10V
• Normal: 0V
• Sample rate: 48 kHz

Reset input

• Resets phase of all operators
• Useful in LFO mode / as a modulation source
• Works regardless of lock/free state
• Gate input: 0V / 5V, threshold about 2.5V
• Normal: 0V
• Sample rate: 6 kHz

Per-operator controls

For each operator 1–4:

Lock/Free toggle

• LOCK: ratio-based tuning relative to master pitch
• FREE: independent oscillator/LFO

Ratio knob + Ratio CV

• LOCK: integer multiplier of master pitch
• Range: x1/11 to x11
• FREE: continuous coarse tune for that operator
• VCO mode: 16.35 Hz to 2093 Hz
• LFO mode: 0.511 Hz to 65.41 Hz

Ratio CV input - In FREE, acts as 1V/oct for that operator - Voltage range: -5V to +5V - Normal: 0V - Sample rate: 6 kHz

Detune knob

• Fine tune per operator
• Range: ±6 semitones

Shape knob + Shape CV

• Morphs waveform:
• sine → triangle → square → saw
• Good starting point for clean FM: full CCW = sine

Shape CV input - Voltage range: -5V to +5V - Normal: 0V - Sample rate: 6 kHz

Gain CV

• Controls operator level and how strongly it modulates destinations
• Think of it like a built-in VCA for both audio output and FM send intensity
• Normalled to full gain

Gain CV input - Voltage range: 0V to +5V - Normal: +5V - Sample rate: 6 kHz

Mod 1 / 2 / 3 / 4 knobs

• FM send amounts from this operator to Operators 1–4
• Includes self-modulation
• Effective send level depends on operator Gain

External AR FM section

The external AR FM source behaves like another modulator with its own send row.

AR FM Gain knob

• Sets incoming external modulation level
• Adjust to avoid clipping

AR FM clipping LED

• Red LED = input clipping/distortion
• Reduce AR FM Gain if it lights

Gain AR FM CV input

• VCA for external modulation amount
• Normalled to full gain
• Voltage range: 0V to +5V
• Normal: +5V
• Sample rate: 6 kHz

AR FM Mod 1–4 knobs

• Amount of external audio-rate modulation sent to Operators 1–4

Algo expander

Adds saved FM-routing “algorithms” and crossfading.

What it stores

Only the modulation matrix settings: - all Mod 1–4 knobs for the 4 operators - AR FM Mod 1–4 knobs

Slots

• A
• B
• C
• Live = current actual knob positions

Buttons

• Long press A/B/C: save into that slot
• Short press a slot: select it into the crossfade pair
• Press two slots to define left/right endpoints
• Double-tap Live to use only current knob positions

Crossfade knob / CV

• Crossfades between selected left/right algorithms
• Manual text does not specify CV voltage range for expander crossfade jack

Important behavior

• If using only A/B/C and not Live, the physical Mod knobs on Quad Operator are ignored

Input / output reference

Inputs

Master inputs

Per-operator inputs

Outputs

Full control reference

Knobs

Master

• Coarse — master tuning
• Fine — master fine tuning

Per operator 1–4

• Ratio
• Detune
• Shape
• Mod 1
• Mod 2
• Mod 3
• Mod 4

External AR FM

• AR FM Gain
• AR FM Mod 1
• AR FM Mod 2
• AR FM Mod 3
• AR FM Mod 4

Algo expander

• Crossfade

Toggles

• VCO/LFO
• Operator 1 Lock/Free
• Operator 2 Lock/Free
• Operator 3 Lock/Free
• Operator 4 Lock/Free

Buttons

• Algo A
• Algo B
• Algo C
• Algo Live

Practical patch tips

For clean/harmonic FM

• Keep operators in LOCK
• Use integer ratios
• Keep Detune at noon
• Start with sine waves
• Add modulation slowly

For animated FM

• Patch envelopes/LFOs to Gain 1–4
• This changes both output level and FM depth dynamically

For independent oscillator bank use

• Put operators in FREE
• Use each output separately
• Ratio CV becomes per-operator pitch CV

For gnarlier tones

• Use:
• non-sine shapes
• self-modulation
• FREE mode
• detuning
• external AR FM
• feedback-style patches with locked operators

Calibration

If pitch tracking seems off:

Patch:

• Op 1 → Ratio 1
• Op 2 → Ratio 2
• Op 3 → Ratio 3
• Op 4 → Ratio 4 and 1V/Oct via unbuffered split

Important: - Use Op 4 for the split to 1V/Oct - Use an unbuffered mult/splitter

Trigger calibration:

1. Flip Operator 1 Lock/Free once
2. Flip Operator 2 Lock/Free once
3. Flip Operator 3 Lock/Free once
4. Flip Operator 4 Lock/Free once
5. Flip VCO/LFO switch 5 times quickly

Success indication: - Gain indicator LEDs blink twice

Specs

Quad Operator

• Width: 30 hp
• Depth: 25 mm
• Power: +12V 140 mA, -12V 13 mA

Algo expander

• Width: 4 hp
• Depth: 25 mm
• Power: +12V 5 mA, -12V 0 mA

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