SQUELCRUDE is a monophonic acid bass synthesizer specialized for TB-303 style squelching basslines. It features aggressive resonance and filter envelopes, slides and accents, and a step sequencer with selectable key and scale. In addition to basslines, it can also be used for leads, drones, and special sound effects.

1. Quick Start

1. Load SQUELCRUDE onto an instrument track in your DAW (or launch the standalone app if not using a DAW).
2. Choose a preset using the preset bar at the top of the window. Start with 01 ACID RIFF 303.
3. Play the keyboard to check the sound. The lower range (around C1–C3) is its sweet spot.
4. Try turning CUTOFF and RESO in the FILTER panel. These two controls shape the characteristic acid squelch.
5. Adjusting DECAY in the ACID panel and ENV MOD in the FILTER panel changes the speed and depth of the squelch.
6. To generate a phrase automatically, turn on SEQ ON in the bottom SEQUENCER panel, press RANDOM, and hold down a key on your keyboard.

2. Screen Layout

Header

• The section at the very top of the window. The logo is on the top left (with the version string to the right of the brand line), followed by the preset bar on the right.

OSCILLATOR

• The sound generation section. In addition to two main oscillators (OSC A and OSC B), it includes a SUB oscillator tuned one octave below.
• Waveforms can be selected from SAW / SQR / PLS / TRI. Classic acid character is produced using SAW and SQR.
• SUB is an independent sound source. Even if A and B levels are set to 0, SUB will still sound. Turn it up when you want to reinforce low-end weight.

FILTER

• The heart of this instrument. CUTOFF controls brightness, and RESO determines the intensity of the resonance peak.
• Turning RESO all the way up causes the filter to self-oscillate, producing a tone even without audio input. This is by design. 30 DRONE is a preset that actively utilizes this behavior.
• ENV MOD sets the depth of the filter envelope. At 0 it behaves like a standard bass synthesizer; increasing it brings out the signature acid sound.
• DRIVE adds internal filter saturation, thickening the tone without altering the resonance response.
• The three vertical buttons on the right edge (labeled KEY TRK) choose how closely the filter tracks the played pitch (OFF / 50% / 100%).
• Filter types can be selected from LP24 / LP12 / BP / HP.

ACID

• Shapes the expressive nuances unique to acid bass.
• DECAY controls how quickly the filter squelch falls off, ACCENT controls intensity on hard-struck notes, SLIDE sets the pitch glide time, and VEL>CUT adjusts how much playing velocity affects brightness.
• Accents take effect on hard-played notes (velocity 100 or higher). Hitting accented notes consecutively builds up cumulative intensity.
• SLIDE takes effect when notes are played overlapping (legato). Setting it to ALWAYS glides continuously across all notes.

MASTER

• TONE controls overall brightness tilt, VOLUME controls output level, and PAN sets stereo positioning. You can monitor the output level with the vertical meter on the right edge of the MASTER panel.
• BYPASS is a button located below the MASTER panel that cuts the output. It is also linked to the DAW’s bypass button.

AMP ENVELOPE

• Controls the volume envelope over time. Setting SUSTAIN to 0 creates snappy plucked sounds, while raising it produces sustained notes.

LFO

• Adds periodic modulation. > CUTOFF modulates the filter, and > PITCH modulates pitch.
• Pressing SYNC locks RATE to musical note divisions synchronized to the DAW tempo.
• DELAY sets the time from note strike until modulation begins.

DISTORTION

• Applies distortion post-filter. OD thickens the tone, HARD is aggressive, and FUZZ provides a crushed texture.
• Lowering MIX blends in the dry sound. Use it when you want to add distortion while preserving low-end definition.

SEQUENCER

• A 16-step sequencer. Turn on SEQ ON and hold down a key to loop a phrase rooted at that note.
• Pressing RANDOM automatically generates a phrase strictly within the selected scale. You can edit the steps manually after generation.
• Grid controls: Drag up/down on the top row to adjust pitch, click ACC to toggle accents, click SLD for slides, and click GATE to cycle through Note → Tie → Rest.
• Steps are stored as scale degrees rather than absolute pitches, so playing a different key transposes the entire phrase.
• Knobs from left to right: LENGTH (number of loop steps), SWING (shuffle delay), DENSITY (note density), ACCENT (accent amount), SLIDE (slide amount), and CUT DEPTH (MOD lane modulation depth).
• KEY (C–B) and SCALE are selected via dropdown menus. The ROOT / KEY buttons, RATE (1/8–1/32), and OCT (0 / ±1 / ±2) buttons are arranged on the right side of the SEQUENCER panel.
• The VIEW buttons NOTE / MOD toggle the grid display. The MOD view is a lane for drawing per-step brightness.

UI Scaling

• Right-click the background to choose a display scale of 75% / 85% / 100%. Use this if the entire window does not fit on small laptop screens.
• The selected scale is saved with your song (project) and remembered the next time you open a new instance.

MORPH

• Located at the top of the window, to the right of the InfoBar. Allows you to store two patches and smoothly morph from one to the other.
• Press A to save the current sound to A, and B to save to B (A lights up purple, B lights up pink).
• When both indicator lights are lit, you can move the slider from A to B. The knobs on the screen physically move, allowing you to manually tweak any sound you discover along the way.
• Pressing an illuminated button again clears that snapshot. As long as either snapshot is missing, moving the slider produces no sound change.

3. Parameter Details

CUTOFF (FILTER)

Sets the frequency where the filter begins cutting off sound. Lower values sound darker and muffled, while higher values sound brighter. The acid squelch is created when the envelope moves upward starting from this position.

• Setting it lower and then raising ENV MOD increases the sweep range of the squelch.
• Default: 800 Hz

RESO (FILTER)

Emphasizes the frequencies around the cutoff. Higher values produce a sharper, more pronounced acid character.

• At maximum, the filter self-oscillates and continues ringing even without audio input. Lower it if you want to stop the resonance tone.
• Default: 55 %

ENV MOD (FILTER)

The depth of the filter envelope sweep. This is the most crucial parameter defining the character of this instrument.

• At 0 % it behaves like a standard bass synthesizer; increasing it brings out the signature 303 character.
• Default: 60 %

DECAY (ACID)

Controls how quickly the squelch decays. Shorter times sound snappy, while longer times sound sticky and prolonged.

• For 16th-note phrases, roughly 150–300 ms is an easy-to-use range.
• Default: 250 ms

ACCENT (ACID)

Controls how dramatically accented notes stand out. Volume, brightness, and sharpness change simultaneously.

• Playing hard notes consecutively builds up cumulative intensity, becoming more aggressive. Adds dynamic expression to rapid 16th-note runs.
• Default: 60 %

SLIDE (ACID)

The time over which pitch glides from note to note. Takes effect when notes are played overlapping (legato).

• Setting SLIDE MODE to ALWAYS glides across all notes even when not overlapping.
• Default: 60 ms

KEY TRACK (FILTER)

The three vertical buttons on the right edge of the FILTER panel (labeled KEY TRK). Makes the filter cutoff follow the played keyboard pitch. Has three settings: OFF / 50% / 100%.

• If low notes sound harsh or overly piercing in the highs, set this to 100%. Low bass becomes substantially smoother and more settled.
• Default: 50%

CUT DEPTH (SEQUENCER)

The knob located on the far right of the SEQUENCER knob row. Determines how strongly the brightness curves drawn in the MOD lane affect the cutoff.

• If left at 0, drawing in the lane produces no sound change. Higher values produce greater brightness differences across steps.
• Default: 0 %

SCALE / KEY / ROOT & KEY Modes (SEQUENCER)

Determines the musical notes used by phrases. KEY (C–B) and SCALE are chosen via dropdown menus, and the ROOT / KEY buttons toggle the mode. RANDOM picks notes exclusively from the selected scale.

• ROOT: The played note becomes the tonic.
• KEY: Notes are constrained by KEY and SCALE, and the played note sets the phrase starting position. Stays strictly in key.
• Default: MINOR / C / ROOT

SCALE can be selected from 12 types:

• Church Modes: MINOR / MAJOR / DORIAN / PHRYGIAN / MIXOLYDIAN
• Minor Variations: HARM MINOR (Harmonic Minor) / MEL MINOR (Melodic Minor) / PHRYG DOM (Phrygian Dominant: has a Spanish flavor, great for acid and psychedelic riffs)
• Pentatonic & Blues: PENT MIN (Minor Pentatonic) / PENT MAJ (Major Pentatonic) / BLUES
• Unrestricted: CHROMATIC (All 12 semitones; phrases can drift outside conventional keys)

DENSITY / ACCENT / SLIDE (SEQUENCER)

Defines phrase tendencies: note density, accent frequency, and slide frequency.

• Turning these knobs immediately regenerates the phrase in place. There is no need to press RANDOM again. The phrase tendency evolves while you listen, allowing you to fine-tune it by ear.
• As a consequence, any steps manually edited will be overwritten as soon as these three knobs are turned. Perform manual tweaks after settling on the overall tendency.
• Default: 75 % / 30 % / 25 %

MORPH (Header)

Morphs smoothly across two stored sound snapshots, A and B. Moving the slider physically moves the knobs on the screen.

• Only applies to continuous knobs and controls. Switched controls like waveforms and filter types do not move, preventing unwanted intermediate settings from being engaged during transitions.
• SEQUENCER settings are excluded. Only patch tone is morphed, keeping the currently playing phrase intact.
• When stopped at either extreme (0 % or 100 %), tweaking knobs on the interface folds those adjustments directly into that snapshot. There is no need to press A or B again. This folding occurs only during manual slider movements; it is not triggered during DAW automation playback, ensuring saved A / B snapshots are never altered during playback.
• Supports DAW automation. MORPH movement can be recorded and automated. Knobs on the screen animate along with automation playback. However, if individual knobs also have their own automation lanes, both MORPH and individual lanes will compete for control. Since priority depends on the DAW, avoid automating both simultaneously.
• Default: 0 % (Neither A nor B saved)

4. Recommended Settings

Classic Acid Riff

OSC A WAVE: SAW
CUTOFF:     400 Hz
RESO:       75 %
ENV MOD:    70 %
ACID DECAY: 220 ms
ACCENT:     80 %
AMP SUSTAIN: 0 %

Deep Sub Bass

OSC A LEVEL: 60 %
SUB:         90 %
CUTOFF:      200 Hz
RESO:        20 %
ENV MOD:     20 %
KEY TRACK:   100%
DIST TYPE:   OFF

Auto-generating Phrases in Key

SEQ ON:      On
ROOT/KEY:    KEY
KEY:         Song Key
SCALE:       MINOR
RATE:        1/16
DENSITY:     75 %

Blending Two Patches (MORPH)

1. Create a dark patch (lower CUTOFF / lower RESO) -> Save to A
2. Switch presets or tweak toward a bright sound
   (higher CUTOFF / higher RESO / higher DIST AMOUNT) -> Save to B
3. Move the MORPH slider slowly from 0 % to 100 %

In addition to manual movement following song arrangements, you can also stop halfway to use an intermediate hybrid tone of A and B as a new starting point. If you like the intermediate sound, you can save it directly as a preset.

5. Requirements

6. Installation & Uninstallation

Installation (Windows)

1. Extract the downloaded ZIP file.
2. Copy the SQUELCRUDE.vst3 folder to the following location:
   C:\Program Files\Common Files\VST3\
3. Launch your DAW and perform a plugin rescan.
4. To use as standalone, launch SQUELCRUDE.exe directly. On first launch, you will need to configure your audio device and MIDI input settings.

Installation (Mac)

1. Extract the downloaded ZIP file.
2. To use as a plugin, copy SQUELCRUDE.vst3 to ~/Library/Audio/Plug-Ins/VST3/, and copy SQUELCRUDE.component to ~/Library/Audio/Plug-Ins/Components/. To use as standalone, copy SQUELCRUDE.app to your “Applications” folder (where ~ represents your home folder. In Finder, open the “Go” menu, choose “Go to Folder…”, paste the path, and press Return).
3. Open Terminal (Applications → Utilities → Terminal), paste the following lines one by one, and press Return for each. You may skip lines for formats you do not use. If nothing is displayed, the command succeeded:

   cd ~/Library/Audio/Plug-Ins
   xattr -dr com.apple.quarantine VST3/SQUELCRUDE.vst3
   xattr -dr com.apple.quarantine Components/SQUELCRUDE.component
   xattr -dr com.apple.quarantine /Applications/SQUELCRUDE.app

   If you do not run this, macOS will show messages such as “is damaged and cannot be opened” or “cannot be opened because the developer cannot be verified”, preventing the DAW from loading the plugin (and preventing the app from launching). These commands only remove the quarantine attribute that macOS attaches to downloaded files (you must run these commands again if you reinstall or update the plugin).

4. Launch your DAW and perform a plugin rescan (if AU does not appear in Logic Pro or other DAWs, restart your Mac).

Uninstallation

Windows: Delete the C:\Program Files\Common Files\VST3\SQUELCRUDE.vst3 folder. To completely remove settings and user presets, delete %APPDATA%\Tonecraft Tokyo\SQUELCRUDE\.

Mac: Delete the copied SQUELCRUDE.vst3, SQUELCRUDE.component, and SQUELCRUDE.app files. To also remove settings and user presets, delete ~/Library/Tonecraft Tokyo/SQUELCRUDE/.

7. Troubleshooting

• Plugin does not appear in DAW
  • Check that the destination path is C:\Program Files\Common Files\VST3\ (or under ~/Library/Audio/Plug-Ins/ on Mac), and perform a plugin rescan in your DAW. If you copied files while your DAW was running, changes may not take effect until restarted.
• Warning appears on first launch
  • Because the software is not code-signed, Windows SmartScreen may display a warning. Click “More info” and then choose “Run anyway” to proceed.
  • On Mac, if a message such as “is damaged and cannot be opened” or “cannot be opened because the developer cannot be verified” appears, run the commands in Step 3 of Installation (Mac).
• No sound produced
  • Check whether BYPASS is turned on or MASTER VOLUME is turned all the way down. In standalone mode, also check your audio device and MIDI input settings.
• Sound continues ringing even after releasing keys
  • When RESO is turned all the way up, the filter self-oscillates and continues ringing without audio input. Lower RESO to stop the self-oscillation.
• Sound is produced even with OSC A and OSC B levels set to 0
  • SUB is an independent sound generator. Set SUB level to 0 as well.
• Sequencer phrase does not match song key
  • Switch ROOT/KEY to KEY, and match KEY and SCALE to your song. In ROOT mode, the played note is treated directly as the tonic.
• Sequencer settings do not change when switching presets
  • This is by design. Presets manage tone patches, while the sequencer manages performance parameters. You can switch presets during performance without interrupting the phrase.
• Drawing in the MOD lane produces no sound change
  • CUT DEPTH is set to 0. Raise CUT DEPTH. The lane draws the modulation shape, but this knob determines how strongly it takes effect.
• Moving the MORPH slider does nothing
  • Both A and B indicator lights must be lit. If either snapshot is missing, there is no destination to morph toward and nothing will happen.
• Moving MORPH does not move SEQUENCER knobs or switch waveforms
  • This is by design. MORPH only affects continuous patch tone knobs; SEQUENCER settings and stepped controls (such as waveforms and filter types) are excluded.
• Individual knob automation does not take effect when playing back MORPH automation
  • The same knob is being automated from both MORPH and an individual lane. Because MORPH controls multiple patch knobs simultaneously, layering individual automation lanes causes conflicting control. Use one or the other.

8. Notes

• This product is distributed free of charge (freeware) “AS IS”, without support.
• The source code is proprietary and not public.
• All copyrights to this product belong to Tonecraft Tokyo.
• Modification, reverse engineering, redistribution, and resale of this product are strictly prohibited (please download only from the Tonecraft Tokyo official website or Gumroad).
• Free for both commercial and non-commercial use.
• This product uses JUCE.

9. Disclaimer

• This product is provided “AS IS”, without warranty of any kind, express or implied, including but not limited to merchantability, fitness for a particular purpose, and non-infringement of third-party rights.
• Tonecraft Tokyo is not liable for any damages arising from the use of, or inability to use, this product, including but not limited to loss or corruption of project files or audio data, equipment malfunction, lost working time, or lost profits.
• Operation is not guaranteed for every combination of DAW, operating system, and hardware.
• Specifications may change, and the product may be discontinued, without notice.
• Use this product at your own risk. Back up your projects before important work.