Melicum

Turn up your HDMI and DisplayPort display from the keyboard, like the built-in speakers. Then shape the sound.

Download for macOS Source on GitHub

macOS 14.2+
Apple silicon & Intel
Free · GPL-3.0
Audio stays on your Mac

Melicum main window: audio output set to a Dell monitor over HDMI, volume at 42 percent, balance, boost, output spectrum and the equalizer

The problem

macOS greys out the volume for most displays.

HDMI and DisplayPort outputs usually have no hardware volume control, so the slider is disabled and the volume keys show a crossed-out speaker. You end up reaching for the monitor's buttons.

BeforeVolume slider disabledKeys do nothing on an HDMI display. Volume lives in the monitor's on-screen menu.

With MelicumNative slider and volume keysSoftware gain on the digital stream, kept in sync with the macOS volume and mute controls.

Features

A volume knob first. A full audio desk when you want one.

HDMI & DisplayPort volume

Volume, mute, balance and up to 12 dB of boost for any output, even when the display has no volume of its own.

0–100% · ±balance · 0–12 dB boost

Native volume keys

An optional system component enables the macOS volume slider and keys, with volume and mute synchronized both ways.

Optional HAL component

Parametric equalizer

Basic tone controls, ten fixed bands, or an expert mode with bell, shelf, pass, notch and band-pass filters.

Up to 64 filters · AutoEQ import

Per-app mixer

Give each application its own level, grouped by bundle, so a video call and music no longer fight.

Separate tap per app

Spatial audio

An original stereo reverb with five spaces, from a small room to a cathedral, plus soundstage width.

5 rooms · mid/side width

Audio Units & presets

Chain installed effects, then save everything as a super preset that follows an output or an app.

12 effects · JSON import/export

How it works

One tap, one callback, one clock.

Melicum captures system audio with Core Audio process taps, processes it in a realtime C engine and plays it on the display, sharing the display's clock to avoid drift.

Your appsMusic, video and calls play to the Melicum output.
Process tapCore Audio captures them, excluding Melicum itself to prevent feedback. The macOS slider and volume keys control this output.
Melicum engineRealtime C with no allocations: volume, EQ, mixer, reverb, Audio Units and peak protection.
DisplayThe HDMI or DisplayPort output plays the result and provides the clock.

Gain applied once

The optional virtual output exposes standard volume and mute to macOS. Its loopback is unused; Melicum applies the gain in its own engine, never twice.

Safe to stop

Disabling or quitting closes the taps and restores the previous output. If Melicum exits unexpectedly, the virtual output disappears within five seconds.

Local only

Audio is processed in memory on your Mac. Nothing is recorded to disk or sent over the network.

Screenshots

Graphite, cream and one red needle.

The interface takes its colors from the icon: a graphite audio console, cream controls and restrained red indicators. Master controls stay visible as you move between panels. The original logo is unchanged.

Native SwiftUI views shown with example device, meter and preset data. Select an image to view it at full size.

Redesigned master console and expert equalizer — **Main window**Persistent output, volume, balance, boost and spectrum above the EQ editor.

Independent application volume and mute controls — **App mixer**Keep music, a browser and calls at independent levels.

Spatial audio switch, room selector, reverb mix and stereo width — **Spatial audio**Five rooms, a reverb mix and stereo width.

Audio Unit effects panel with Add effect action — **Audio Units**Add compatible installed effects and edit their parameters.

Saved presets, language, startup and automatic update preferences — **Presets and settings**Save setups and configure language, startup and update checks.

Compact menu bar panel with master volume and Open panel action — **Quick menu**Volume, mute, power and update checks from the menu bar.

Settings

Your setup, ready when you need it.

Audio presets and application preferences are independent, so recalling an EQ setup does not change your language or startup choices.

Save the whole sound

Super presets include volume, EQ, app levels, reverb and Audio Unit parameters. Link one to an output or an application, or import and export settings as JSON.

Choose how it starts

Launch at login opens Melicum when you sign in. Enable audio on launch separately activates the saved output; it is off by default. If that output is unavailable, processing stays off.

Five languages

Switch immediately between English, Italian, French, German and Spanish under Presets. Read the full guide for every control and preset setting.

Signed updates

Automatic checks. Installation with your approval.

Melicum checks for stable releases approximately once a day by default. Turn automatic checks on or off under Presets → Updates, or check manually from the app or quick menu.

A verified download

Sparkle verifies the signed feed, archive signature and Apple code signing. Drafts and prereleases are excluded from the stable update feed.

Your settings stay

The app asks before downloading and installing. It restores the physical output before quitting, retains presets and preferences, and follows your startup choice after relaunch.

The audio component

App updates do not silently replace the optional HAL component. When a release includes a component update, run its included Enable system volume… installer separately.

Install

Four steps to a working volume key.

Download and open
Get the latest .dmg from Releases and drag Melicum to Applications. Builds are signed and notarized by Apple.
Pick your display
Choose the monitor or audio device under Audio output.
Enable audio
Click Enable audio and allow system audio recording when macOS asks.
Unlock the volume keys
Click Enable system volume… and authorize the installer. The macOS slider and keys now control your display.

Build from source

Swift, Core Audio and C.

Requires Xcode. The system volume component builds on BlackHole, included as a submodule.

# clone with the BlackHole submodule
git clone --recurse-submodules \
  https://github.com/debba/melicum.git
cd melicum

# test, then build the driver and the app
swift test
./scripts/build-system-volume.sh
./scripts/build.sh
open build/Melicum.app

The name

melicusLatin · "lyrical, for singing"

Melic poetry was sung to the lyre. The icon draws one as an equalizer: the yoke is an EQ curve with three hollow nodes, each string ends on that curve like a frequency band, and the sound box has the profile of an HDMI receptacle.

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