The Mono Hawk

The Mono Hawk is a chromatic tuner for guitar and bass that runs on Linux as an LV2 plugin, with its own hardware-style interface. It tracks a single note to better than a cent, down to a 5/6-string bass low B (~31 Hz), and pairs that precision with a display you can read at a glance while you play.

The front panel

Everything you need while tuning is on one face. From left to right:

• The note window (top left) shows the note you're playing — letter, sharp and octave. Sharps only, so E-flat reads as D#.
• The thin strip along the top edge is an input-level meter, so you can see signal is actually reaching the plugin.
• The chevron meter in the middle is how far off you are. The chevrons light inward from the edges: toward the left and blue when you're flat (tune up), toward the right and amber when you're sharp (tune down). The centre glows white when you land in tune, and a short pointer marks the exact spot. Colours are chosen to stay distinct for colour-blind eyes — flat and sharp are never red-versus-green.
• The string row underneath shows the open strings of the selected tuning, low string on the left. As you tune each string in, its letter latches lit and stays lit — a checklist you can work through in any order.
• The line under the row names the current tuning (Drop D ▾) and is the tuning selector — click it to open the menu.
• Bottom left, 440 Hz ▾ is the A4 reference; click to change it.
• On the right are TONE and MUTE, and the hawk badge. The badge opens the settings window.

How it tunes

Play a string and the note window and chevron meter tell you the note and how far off it is. The string row doubles as a checklist — each string's letter lights up the moment you tune it in and stays lit, so you can work through the whole instrument in any order. When the last one lands, the row and badge glow briefly and then reset for the next instrument.

Precision, and what "in tune" means

The detector works in two stages. A coarse stage picks the right note (and is careful about octaves — low strings have a weak fundamental and overtones that sit slightly sharp, an easy way to misread the pitch an octave too high). A fine stage then tracks the phase of the signal to pull the cents down below a cent. On a steady signal it resolves to about a tenth of a cent — strobe-tuner territory — and it reaches down to a 5/6-string bass low B, around 31 Hz.

"In tune" is a small window around the target, not a single razor-thin point — real strings drift and a perfectly strict tuner would never settle. That window is the In-Tune Tolerance in the settings, two cents by default. Inside it, the meter centre and the string letter read white. The measurement itself is far finer than that window; the band just decides when to call it good.

Settings

Click the hawk badge to open Advanced Settings.

• Dim Amount — how far the MUTE button pulls the output down, in dB. Set it deep if you want near-silence while you tune, or leave it shallow to keep playing quietly.
• In-Tune Tolerance — the half-width of the in-tune window, in cents (default 2.0). Smaller is stricter; larger is more forgiving.
• Sensitivity — how readily the detector trusts a weak or noisy signal. Turn it up for quiet pickups or a soft touch; turn it down if it's picking up room noise between notes.
• Ping — a short confirmation tone when a string lands in tune. Off by default; turn it on here if you like the audible cue.

TONE and MUTE

MUTE dims the output by the Dim Amount, so you can tune without the dry note blasting through your chain. The rest of the time the plugin is a clean passthrough — bit-for-bit identical to the input when it isn't dimming — so it can sit permanently on a track.

TONE plays a steady reference pitch for tuning by ear. With it on, the plugin sounds a sine at the selected string's note; tap the note window to step through the strings, and tap the small REF tag to move the tone up an octave into a comfortable register.

Tunings

Fifty of them, picked from a menu that's grouped by instrument and string count rather than dumped in one long list:

• Guitar, six strings: Standard, the drops, the open (major) tunings, cross-note (minor) tunings, modal and suspended tunings like DADGAD, the whole lowered family from E-flat down to F, and the regular tunings (all-fourths, all-thirds, all-fifths, New Standard, Ostrich).
• Guitar, seven and eight strings: standard and drop.
• Bass, four/five/six strings, with drops.

If you don't know what something is tuned to, pick Detect Tuning… from the menu and play the open strings one at a time — it listens and matches the set against the table.

Why there's no polyphonic mode

A polyphonic (all-strings-at-once) detector was prototyped for this project, using the method described in Zhou, Reiss et al. (2009).¹ It is not included here: polyphonic instrument tuning is covered by active patents — originating with the TC Electronic PolyTune and now held by Music Tribe / Behringer — which makes a freely-licensed, open-source polyphonic tuner untenable until those patents expire (around 2030–2031) or are invalidated. So this release is chromatic only. That, rather than any lack of a working method, is why a free and open polyphonic guitar tuner doesn't exist on Linux today.

The method itself is written up in POLYPHONIC-METHOD.md — the knowledge is free even though the product can't be shipped.

¹ R. Zhou, J. D. Reiss, M. Mattavelli, and G. Zoia, "A Computationally Efficient Method for Polyphonic Pitch Estimation," EURASIP Journal on Advances in Signal Processing, vol. 2009, Article ID 729494. doi:10.1155/2009/729494

Building it

You'll need a C++17 compiler, Meson with Ninja, and the LV2, Cairo and Xlib development headers.

meson setup build
meson test -C build      # the detection test suites
ninja -C build           # core, CLI, and the LV2 plugin + GUI

Installing it

Use the install script. It swaps the libraries in atomically — writes a temp file 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.

./scripts/install.sh     # builds, then installs to ~/.lv2/themonohawk.lv2/

In a host like Ardour it shows up as The Mono Hawk Tuner. Put it on a mono track and open its interface. If you rebuild in a way that changes the plugin's port count, remove and re-add it so the host re-reads the ports.

Without a DAW

There's a command-line tuner that reads raw 32-bit-float mono audio from stdin and prints a live ASCII display:

arecord -f FLOAT_LE -c 1 -r 48000 -t raw | ./build/tools/hawk_cli
# or with PipeWire:
# pw-record --rate 48000 --channels 1 --format f32 - | ./build/tools/hawk_cli

How this was made, and the license

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.

Author

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