omx-dsp

The DSP library of OpenMixer: the building blocks of the console (biquads, one-poles, envelopes, gain computers, delay rings, the oversampler) and the effect kernels built from them. The OpenMixer engine and the omx plugins compile the same kernels from this library, so an effect sounds the same on the console and in any other host.

• Plain C11 and -lm. No allocation, lock or system call on the audio path; every state is owned by the caller, so any number of threads can run the kernels on their own states.
• Pre- and postconditions on every function, compiled in with -DOMX_CONTRACTS for testing and absent from a release build.
• Every kernel is tested against its closed form at 44.1, 48, 88.2, 96, 176.4 and 192 kHz, and its output is held bit for bit by golden digests. The dynamics, balance, rotor, limiter and loudness are also tested at 32, 64 and 128 kHz, the other rates of the oracle set.
• Build time only: headers and a static library. Nothing is installed that a running program loads.

Install

Fedora 44, x86_64 or aarch64:

sudo dnf install https://www.openmixer.org/rpm/openmixer-release.noarch.rpm
sudo dnf install omx-dsp-devel

Debian bookworm and trixie, amd64 or arm64 (also Raspberry Pi OS and Zynthian):

curl -fsSLO https://www.openmixer.org/deb/openmixer-release.deb && sudo apt install ./openmixer-release.deb
sudo apt install libomxdsp-dev

Use

cc $(pkg-config --cflags omxdsp) -c my_plugin.c
cc -shared -o my_plugin.so my_plugin.o $(pkg-config --libs omxdsp)

#include <omxdsp/fx/omx_delay.h>

A consumer's CI can check that it calls the library instead of carrying its own copies of what the library exports. The devel package installs omx-dsp-copy-check and the exports file it reads; from the root of the consumer's checkout:

omx-dsp-copy-check --enforce

It scans the tracked C and TypeScript sources (tests, fakes, fixtures, oracles and generated directories excluded) and names each function that defines an exported name or a twin the library's documentation declares, repeats an export's body, carries two of its distinctive constants with the same maths calls, or writes a short export inline, such as 20 * log10(x) or the mono sum 0.5f * (l[i] + r[i]). Without --enforce it only reports. Copies kept on purpose go in omx-dsp-copies.allow at the root, one per line:

tools/measure.c:main | omx_lin_to_db_d | an independent measurement, kept on purpose | owner#12

An entry that no longer covers a copy, or that has no reason or owner, fails the check, so the list only shrinks. omx-dsp-copy-check --help describes every rule.

The library comes in three flavours, each with its own archive and pkg-config file. A program builds against the one that matches its own build, so that its contract and TSan builds also check the library's compiled code:

The contracts and TSan flavours put -DOMX_CONTRACTS (and -fsanitize=thread) in the cflags. The program defines the violation ledger in one of its files with #define OMX_CONTRACT_STORAGE before including the headers.

Building from source and running the tests: BUILDING.md.

Licence

GPL-3.0-or-later.