SoX Plugins for DAWs

The SoXPlugins software package provides plugins for being used in digital audio workstations (DAW); they implement some of the more prominent audio processing effects from SoX as DAW audio plugins.

SoX is a command line audio processing tool for Unix, Windows and Mac OS that transforms source audio files in several formats into other audio files. It provides several standard audio effects (like e.g. filters or reverb) in good quality and with a transparent, open-source implementation.

This plugin implementation is completely free, open-source, platform-neutral and based on the JUCE audio framework. Currently only plugin versions as VST3 under Windows 10, VST3 and AU under MacOSX (x86_64) and VST3 under Linux (x86_64) are provided, but porting to other targets should be straightforward, since building is supported by a platform-neutral CMAKE build file.

The effects provided here are a complete rewrite in C++ of the SoX algorithms for producing (bit-exact) identical renderings in the DAW. This can easily be checked by rendering some audio externally with SoX and internally with the plugins and subtracting the results. Apart from roundoff errors (SoX often uses 32bit integer processing, while the SoXPlugins always uses double floating point processing) the results cancel out with typically a residual noise of -140dBFS.

The main motivation for this package is to be able to play around with effects in a DAW and be sure that the external rendering by SoX will produce exactly the same results. Although SoX does not always provide the "best" effects, it still is a reliable and well-defined audio tool.

Only a selection of SoX effects has been reimplemented as plugins, but those are the ones that are - in my opinion - the more prominent effects in that suite.

Because SoX very often uses rich command line options for its effects, not every effect configuration from SoX can be fully transported into the slider oriented GUI for a plugin. E.g. the compander of SoX allows the definition of a transfer function having multiple segments. Although the internal engine of the SoXPlugins compander implements exactly the same internal segment logic, the user interface only allows the typical definition of a threshold and a compression ratio (with three segments).

Note also that a spiffy user interface is not at all a priority in this project. Also their parameter ranges are somewhat debatable, but they simply reflect the wide parameter ranges of the SoX command-line effect.

The redesign and restructuring has also been done for easier maintenance, because there is some redundancy and unnecessary complexity in the original sources due to their several contributors. Nevertheless - as pointed out - the effects provided here faithfully model the SoX command-line processing.

The following effects are available in this package:

• allpass: a biquad allpass filter two-poled with filter frequency and the filter bandwith (in several units)

• band: a biquad bandpass filter with center filter frequency and the filter bandwith (in several units) and an option for unpitched audio

• bandpass: a biquad filter for bandpass with center filter frequency and the filter bandwith (in several units)

• bandreject: a biquad filter for bandreject with center filter frequency and the filter bandwith (in several units)

• bass: a biquad filter for boosting or cutting bass with a shelving characteristics with settings for filter frequency and the filter bandwith (in several units)

• biquad: a generic biquad (iir) filter with 6 coefficients b0, b1, b2, a0, a1 and a2

• compand: a compander with attack, release, input gain shift, threshold and compression and soft knee; this is a reduced version of SoX compand with only a simple transfer function

• equalizer: a biquad filter for equalizing with settings for the pole count, the filter frequency and the filter bandwith (in several units)

• gain: a volume changer by exact decibels...

• highpass: a biquad filter for highpass with settings for the pole count, the filter frequency and the filter bandwith (in several units)

• lowpass: a biquad filter for lowpass with settings for the pole count, the filter frequency and the filter bandwith (in several units)

• mcompand: a multiband compander with a Linkwitz-Riley crossover filter and for each band a compander with attack, release, input gain shift, threshold and compression and soft knee; again the companders only allow a simple transfer function

• overdrive: a simple tanh distortion with gain and colour specification

• phaser: a phaser effect with sine or triangle modulation

• reverb: a reverb effect (based on Freeverb) with several parameters for the room (like size and HF damping) as well as a possible predelay

• treble: a biquad filter for boosting or cutting treble with a shelving characteristics with settings for filter frequency and the filter bandwith (in several units)

• tremolo: a tremolo effect with sine modulation using a double-sideband suppressed carrier modulation

The installation is as follows:

1. Expand the appropriate binary archive of the SoXPlugins for your platform from this repository into the directory for VST plugins of your DAW.

2. The distribution also contains a documentation pdf file in subdirectory doc and test files in subdirectory test (for details on the regression test see below).

3. When installing the plugins on MacOSX, note that those are not signed; so you have to explicitly remove the quarantine flag from them (e.g. by applying the command sudo xattr -rd com.apple.quarantine «vstPath»).

4. When installing the plugins on Windows, they require the so-called Microsoft Visual C++ Redistributable library. Very often this is already installed on your system; if not, you have to install it from the Microsoft site.

5. Restart your DAW and rescan the plugins. You should now be able to select the SoXPlugins (they are all prefixed with "SoX").

The above diagram gives an example for one of the plugins: this is the UI for the phaser effect.

Here In Gain is the amplification factor for the input in decibels. Delay gives the delay in milliseconds, Decay a factor for the decay within the phaser and Frequency gives the modulation frequency in Hz. The Waveform of the modulation is either sinusoidal or triangular. Out Gain is the volume of the output.

If you are acquainted with the SoX command-line effects, you can see that this is a direct representation of the parameter list in the phaser effect.

If you want to run the test, you also have to have a SoX installation. The test script "makeTestFiles.bat" or "makeTestFiles.sh" in the test directory assumes that SoX is available in the program search path.

The test script produces several sound and noise files and applies SoX audio effects to produces result audio files.

Since there are so many DAWs available, it is hard to provide a test project for each of those. The distribution contains a Reaper project referencing those audio test files and result files in autonomous tracks. Adaption to other DAW should be straightforward.

The project file "testSoXPlugins.rpp" for the Reaper DAW references those test and result files and applies the corresponding effect plugins. Ideally (because the result files have inverted phase), everything should cancel out as shown here:

The detailed user manual can be found here.

This project is a derivative work based on the foundations laid by the SoX community. Although the algorithms used were modified and redesigned, this project would been much more complicated and tedious without this basis.

Hence my thanks go to Chris Bagwell, Nick Bailey, Daniel Pouzzner, Måns Rullgård, Rob Sewell and all the other contributors of the SoX project: without your effort this would not have been possible!

There are two license models for this project:

• The source code is provided with an MIT license.

• The VST and AU files given in the release are provided with an AGPL v3 license since they contain parts of the JUCE framework.

This means that if you do not use the given binaries and compile the source code by yourself, the MIT license applies. If you do use the binaries, then the AGPL v3 license applies.