x42 / phaserotate.lv2

Phase Rotation LV2 plugin

phaserotate.lv2

phaserotate.lv2 is an audio phase rotation plugin.

Phase shift vs. time shift

Time shifting delays a signal by an absolute value in seconds (or samples). While phase shift uses a relative value, a fraction of the wave-length.

When phase shifting a signal, different components of the signal are delayed differently depending on their frequency.

The following figure shows an oscilloscope display of two sine-waves with different frequencies that play concurrently (green and blue) and respective shifted versions of each signal (red, violet).

The left images shows a phase shift by 90deg (1/4 wave-length). Note that the time-delay differs: The sine-wave with the lower frequency (top, red) is delayed further compared to the higher pitched sine-wave (bottom, violet).

In the right image both sine-waves are delayed by the same time. Note how this results in a different phase shift, as both waves differ in their wavelength.

Due to the periodic nature of the signal, a phase shift of +180 deg is equivalent to a shift of -180 deg. The signal is rotated around the unit circle on the complex plane.

Phase rotation

The interesting aspect is that phase rotation does not alter the sound of the signal nor the loudness. However changing the phase vs. frequency relationship between lower and upper harmonics changes the waveform and can affect where the digital peak occurs.

For this reason phase rotation is commonly used by radio stations to reduce the signal peak and make the signal more symmetrical. Phase rotation circuits are also used during mastering to increase headroom. This allows to increase gain and further compress the signal.

Caveat

By nature of the process phase-rotation affects transient response. Similar to a linear-phase EQ, there is also pre-ringing. Use this effect with caution because you are about to become a casualty in the loudness-war against quality. You have been warned.

CLI

In addition to the plugin, there is a command-line tool that can analyze an audio file, and find the phase shift which will result in a minimum peak.

This is for offline analysis and offline processing only, and not installed by default.

Install

Compiling phaserotate.lv2 requires the LV2 SDK, fftw, gnu-make, and a c-compiler.

git clone https://github.com/x42/phaserotate.lv2.git
cd phaserotate.lv2
make

ln -s `pwd`/build ~/.lv2/phaserotate.lv2
#sudo make install PREFIX=/usr

cd cli
make
#sudo make install PREFIX=/usr
./phase-rotate --help

Note to packagers: The Makefile honors PREFIX and DESTDIR variables as well as CFLAGS, LDFLAGS and OPTIMIZATIONS (additions to CFLAGS), also see the first 10 lines of the Makefile.

phaserotate.lv2's Issues

Man page not being built leads to failing install of x42-plugins 20220913

Hi! When trying to install x42-plugins 20220913 I ran into an issue where the man page of this project is not built and therefore fails the installation of the plugins.

install -d /build/x42-plugins/pkg/x42-plugins/
make[1]: [Makefile:233: submodule_check] Error 1 (ignored)
install -d /build/x42-plugins/pkg/x42-plugins//usr/share/man/man1
install -m644 x42-spectr.1 /build/x42-plugins/pkg/x42-plugins//usr/share/man/man1
install -d /build/x42-plugins/pkg/x42-plugins//usr/lib/lv2/mixtri.lv2
make[1]: [Makefile:244: submodule_check] Error 1 (ignored)
install -d /build/x42-plugins/pkg/x42-plugins//usr/lib/lv2/fil4.lv2
install -d /build/x42-plugins/pkg/x42-plugins//usr/share/man/man1
install -d /build/x42-plugins/pkg/x42-plugins//usr/bin
install -m755 build/matrixmixerUI_gl.so /build/x42-plugins/pkg/x42-plugins//usr/lib/lv2/matrixmixer.lv2
install -m644 x42-phaserotate.1 /build/x42-plugins/pkg/x42-plugins/
install -m644 x42-fat1.1 /build/x42-plugins/pkg/x42-plugins//usr/share/man/man1
install -m755 build/sisco.so /build/x42-plugins/pkg/x42-plugins//usr/lib/lv2/sisco.lv2
install -d /build/x42-plugins/pkg/x42-plugins//usr/lib/lv2/spectra.lv2
install -m644 build/manifest.ttl build/mixtri.ttl /build/x42-plugins/pkg/x42-plugins//usr/lib/lv2/mixtri.lv2
install -m644 x42-tuna.1 /build/x42-plugins/pkg/x42-plugins//usr/share/man/man1
install: cannot stat 'x42-phaserotate.1': No such file or directory
install -m755 x42/x42-darc /build/x42-plugins/pkg/x42-plugins//usr/bin
install -m644 build/manifest.ttl build/fil4.ttl /build/x42-plugins/pkg/x42-plugins//usr/lib/lv2/fil4.lv2
make[1]: *** [Makefile:290: install-man] Error 1
make[1]: Leaving directory '/build/x42-plugins/src/x42-plugins-20220913/phaserotate.lv2'
install -d /build/x42-plugins/pkg/x42-plugins//usr/bin
install -m644 build/manifest.ttl build/spectra.ttl /build/x42-plugins/pkg/x42-plugins//usr/lib/lv2/spectra.lv2
install -d /build/x42-plugins/pkg/x42-plugins//usr/lib/lv2/fat1.lv2
make: *** [Makefile:40: phaserotate.lv2] Error 2
make: *** Waiting for unfinished jobs....

Makefile does not set BINDIR and MANDIR

The Makefile currently does not set BINDIR or MANDIR which leads to the jack application and man page being installed to root (/).

How to build for Windows

Hi, thank you for your great work in x42 plugins.

I need some help in how to build the static binaries to be used on Windows (specially the CLI). I am using Windows 11, with Arch Linux via WSL2 and mingw64 for crosscompile. But with the instructions provided I can only build for Linux.

I am trying to use this code:
git clone https://github.com/x42/phaserotate.lv2.git
cd phaserotate.lv2
make submodules
make XWIN=x86_64-w64-mingw32

But it never compiles the Windows static binaries. Any help on how I could do it would be very appreciated.