Valve Howler

Valve Howler is a smooth overdrive for guitar and bass that runs on Linux as a mono LV2 plugin, with its own hardware-style interface. It is the classic green screamer-style circuit, modelled from the schematic rather than fitted to a curve or captured from a unit: every stage is derived from the components and their equations, and its coefficients are generated from the netlist.

This is an independent product and is not affiliated with, endorsed by, or connected to any pedal manufacturer. The variant names describe circuit topology, not brands.

Full disclosure: This plugin was vibe-coded.

Valve Howler was developed by a musician/audio engineer (NiLace) directing Claude (Anthropic's AI) through natural language conversation. The author described what the plugin should do, how it should sound, and how it should look. Claude wrote the C++ code, the DSP algorithms, the UI rendering, the build system, and this README.

The author is not a professional programmer, though he can read C++. Every line of code in this project was generated by AI, then tested and validated by the author in real-world audio production with Ardour on Linux.

If AI-generated code is a concern for you, this is your notice. The plugin works and it sounds good — but you should know how it was made.

It's the overdrive that made the sound of a thousand records: a mild, sweet clipping with a strong midrange hump — more a push into the front of an amp than a distortion in its own right. Turn the drive up and it thickens and compresses rather than tearing; back it off and it works as a clean boost with attitude.

The model comes from the circuit, so the controls behave the way the hardware's do rather than the way three independent DSP blocks would. The tone control's corner moves with the drive, the output stage loads the tone stage, the supply rail moves under the signal — none of that is added flavour, it falls out of solving the same network the pedal is. The arbiter throughout development was ngspice running the same netlist: not a listening test, and not a capture of somebody's unit.

The non-linear part runs at 4× internally so its harmonics don't fold back into the audible band. That costs 7 samples of latency at any session rate; the plugin reports it and the host compensates.

Three knobs and a footswitch, like the pedal:

• Drive — how hard the signal is pushed into the clipping stage. At the low end it's a clean boost; at the top it's thick and compressed.
• Tone — the treble tilt after the clipping stage. Turning it up opens the top end; turning it down rolls it off and leaves the midrange hump alone.
• Level — the output volume.
• The footswitch is the bypass. It is wired to the host's standard enabled control, so the host understands it as a bypass and can automate it, rather than it being an invented toggle only this plugin knows about. The name lights up when the pedal is engaged.

Drag a knob up or down to set it. Along the bottom is the variant selector.

Two details worth knowing about the bypass. The dry signal leaves delayed by the same 7 samples the plugin reports — deliberately, so that mixing in parallel with a dry path stays aligned instead of eating a comb filter. And it crossfades over about 10 ms rather than switching hard, because the engine's resting output isn't zero and a hard jump would click.

Four rows, and they are two circuits crossed with two laws for the tone knob:

The two circuits differ in the pair of resistors at the output. It is a subtle difference — a slightly different output level and load — not a different pedal.

W is the taper of the real potentiometer, and it is the default: faithful, but that means the circuit crams most of its tone range into the last part of the sweep. L keeps exactly the same circuit and redistributes the knob's travel so the change per degree of rotation comes out even. It is deliberately not faithful — it is a voicing choice — which is why it lives in its own row instead of replacing the honest one.

Only the rows whose sources are settled are offered. Where two real models differ only in a part this model cannot tell apart, they share one row rather than appear as separate modes that sound identical.

Stated here so it doesn't have to be inferred:

• The pedal's switching system — the JFETs and the CMOS flip-flop that do the bypass in the hardware — is out of scope. The bypass is the host's, as described above. The input and output buffers are modelled in full, and those are the part that actually colours the signal.
• The loading of your guitar's pickups. That happens in the analogue domain before the converter, so no plugin can do it. It isn't a shortcoming of this one.

The easy way — no compiler needed. Grab the prebuilt bundle from the Releases page and drop it into your personal LV2 folder:

mkdir -p ~/.lv2
tar -xzf valvehowler.lv2.tar.gz -C ~/.lv2/

That leaves valvehowler.lv2/ under ~/.lv2/. Restart your host (or rescan plugins) and it shows up as Valve Howler — in Ardour or any other LV2 host (Carla, Qtractor, Zrythm, REAPER with LV2…). Put it on a mono track. To uninstall, delete the folder. If your host scans a different location, extract there instead (the system-wide path is usually /usr/lib/lv2 or /usr/local/lib/lv2).

The bundle is a 64-bit x86 build for Linux. What changed in each version is listed in CHANGELOG.md.

You'll need a C++17 compiler, the LV2 development headers, and Cairo, Xlib and FreeType for the interface. Nothing else is vendored.

make                                           # plugin + interface + fonts
make install                                   # installs to ~/.lv2/valvehowler.lv2/
make install INSTALL_DIR=/usr/local/lib/lv2    # or wherever your host scans

make install is atomic — it writes a temporary directory and renames it over the old one — because copying over a .so while a host has it memory-mapped will corrupt the running process and take the host down with it. make test runs a smoke check over the bundle it just built: that both entry points survived the hidden-visibility build, and that every file the interface loads at run time is actually in it.

• Fonts (assets/fonts/) — Archivo, Barlow Condensed and Space Mono, under the SIL Open Font License 1.1 (full text and copyright notices sit beside them). They stay under the OFL and are not relicensed under the GPL. They travel inside the bundle because the interface loads them directly rather than through the system's font configuration.

This plugin was built mainly with Claude Code (Anthropic's AI coding agent), working from my direction on the DSP, the design, and the testing. I can read C++, but I have not reviewed every line by hand — so please treat it accordingly:

• No warranty. It works in my own testing, but it carries no guarantees of any kind.
• No support. This is a personal project; I can't promise help, fixes, or answers.
• Help is welcome. If you read code, spot bugs, or want to improve it, review and contributions are genuinely appreciated — that's a big part of why it's open.

Released under the GNU General Public License v3.0 or later — see LICENSE.

Made by NL Sounds — https://github.com/NiLace · nilace@nylarea.com