Ubuntu Manpage: libpipewire-module-filter-chain

Provided by: libpipewire-0.3-modules_1.2.7-1_amd64

NAME

       libpipewire-module-filter-chain - Filter-Chain

DESCRIPTION

       The filter-chain allows you to create an arbitrary processing graph from LADSPA, LV2 and
       builtin filters.

       This filter can be made into a virtual sink/source or between any 2 nodes in the graph.

       The filter chain is built with 2 streams, a capture stream providing the input to the
       filter chain and a playback stream sending out the filtered stream to the next nodes in
       the graph.

       Because both ends of the filter-chain are built with streams, the session manager can
       manage the configuration and connection with the sinks and sources automatically.

MODULE NAME

       libpipewire-module-filter-chain

MODULE OPTIONS

       • node.description: a human readable name for the filter chain

       • filter.graph = []: a description of the filter graph to run, see below

       • capture.props = {}: properties to be passed to the input stream

       • playback.props = {}: properties to be passed to the output stream

FILTER GRAPH DESCRIPTION

       The general structure of the graph description is as follows:

        filter.graph = {
            nodes = [
                {
                    type = <ladspa | lv2 | builtin | sofa>
                    name = <name>
                    plugin = <plugin>
                    label = <label>
                    config = {
                        <configkey> = <value> ...
                    }
                    control = {
                        <controlname|controlindex> = <value> ...
                    }
                }
                ...
            ]
            links = [
                { output = <portname> input = <portname> }
                ...
            ]
            inputs = [ <portname> ... ]
            outputs = [ <portname> ... ]
            capture.volumes = [
                { control = <portname>  min = <value>  max = <value>  scale = <scale> } ...
            ]
            playback.volumes = [
                { control = <portname>  min = <value>  max = <value>  scale = <scale> } ...
            ]
       }

   Nodes
       Nodes describe the processing filters in the graph. Use a tool like lv2ls or listplugins
       to get a list of available plugins, labels and the port names.

       • type is one of ladspa, lv2, builtin or sofa.

       • name is the name for this node, you might need this later to refer to this node and its
         ports when setting controls or making links.

       • plugin is the type specific plugin name.

         • For LADSPA plugins it will append .so to find the shared object with that name in the
           LADSPA plugin path.

         • For LV2, this is the plugin URI obtained with lv2ls.

         • For builtin and sofa this is ignored

       • label is the type specific filter inside the plugin.

         • For LADSPA this is the label

         • For LV2 this is unused

         • For builtin and sofa this is the name of the filter to use

       • config contains a filter specific configuration section. Some plugins need this.
         (convolver, sofa, delay, ...)

       • control contains the initial values for the control ports of the filter. normally these
         are given with the port name but it is also possible to give the control index as the
         key.

   Links
       Links can be made between ports of nodes. The portname is given as
       <node_name>:<port_name>.

       You can tee the output of filters to multiple other filters. You need to use a mixer if
       you want the output of multiple filters to go into one filter input port.

       links can be omitted when the graph has just 1 filter.

   Inputs and Outputs
       These are the entry and exit ports into the graph definition. Their number defines the
       number of channels used by the filter-chain.

       The <portname> can be null when a channel is to be ignored.

       Each input/output in the graph can only be linked to one filter input/output. You need to
       use the copy builtin filter if the stream signal needs to be routed to multiple filters.
       You need to use the mixer builtin plugin if multiple graph outputs need to go to one
       output stream.

       inputs and outputs can be omitted, in which case the filter-chain will use all inputs from
       the first filter and all outputs from the last filter node. The graph will then be
       duplicated as many times to match the number of input/output channels of the streams.

   Volumes
       Normally the volume of the sink/source is handled by the stream software volume. With the
       capture.volumes and playback.volumes properties this can be handled by a control port in
       the graph instead. Use capture.volumes for the volume of the input of the filter (when for
       example used as a sink). Use playback,volumes for the volume of the output of the filter
       (when for example used as a source).

       The min and max values (defaults 0.0 and 1.0) respectively can be used to scale and
       translate the volume min and max values.

       Normally the control values are linear and it is assumed that the plugin does not perform
       any scaling to the values. This can be changed with the scale property. By default this is
       linear but it can be set to cubic when the control applies a cubic transformation.

BUILTIN FILTERS

There are some useful builtin filters available. You select them with the label of the
filter node.

Mixer
Use the mixer plugin if you have multiple input signals that need to be mixed together.

The mixer plugin has up to 8 input ports labeled 'In 1' to 'In 8' and each with a gain
control labeled 'Gain 1' to 'Gain 8'. There is an output port labeled 'Out'. Unused input
ports will be ignored and not cause overhead.

Copy
Use the copy plugin if you need to copy a stream input signal to multiple filters.

It has one input port 'In' and one output port 'Out'.

Biquads
Biquads can be used to do all kinds of filtering. They are also used when creating
equalizers.

All biquad filters have an input port 'In' and an output port 'Out'. They have a 'Freq',
'Q' and 'Gain' control. Their meaning depends on the particular biquad that is used. The
biquads also have 'b0', 'b1', 'b2', 'a0', 'a1' and 'a2' ports that are read-only except
for the bq_raw biquad, which can configure default values depending on the graph rate and
change those at runtime.

We refer to https://arachnoid.com/BiQuadDesigner/index.html for an explanation of the
controls.

The following labels can be used:

• bq_lowpass a lowpass filter.

• bq_highpass a highpass filter.

• bq_bandpass a bandpass filter.

• bq_lowshelf a low shelf filter.

• bq_highshelf a high shelf filter.

• bq_peaking a peaking filter.

• bq_notch a notch filter.

• bq_allpass an allpass filter.

• bq_raw a raw biquad filter. You need a config section to specify coefficients per sample
rate. The coefficients of the sample rate closest to the graph rate are selected:

filter.graph = {
nodes = [
{
type = builtin
name = ...
label = bq_raw
config = {
coefficients = [
{ rate = 44100, b0=.., b1=.., b2=.., a0=.., a1=.., a2=.. },
{ rate = 48000, b0=.., b1=.., b2=.., a0=.., a1=.., a2=.. },
{ rate = 192000, b0=.., b1=.., b2=.., a0=.., a1=.., a2=.. }
]
}
...
}
}
...
}

Convolver
The convolver can be used to apply an impulse response to a signal. It is usually used for
reverbs or virtual surround. The convolver is implemented with a fast FFT implementation.

The convolver has an input port 'In' and an output port 'Out'. It requires a config
section in the node declaration in this format:

filter.graph = {
nodes = [
{
type = builtin
name = ...
label = convolver
config = {
blocksize = ...
tailsize = ...
gain = ...
delay = ...
filename = ...
offset = ...
length = ...
channel = ...
resample_quality = ...
}
...
}
}
...
}

• blocksize specifies the size of the blocks to use in the FFT. It is a value between 64
and 256. When not specified, this value is computed automatically from the number of
samples in the file.

• tailsize specifies the size of the tail blocks to use in the FFT.

• gain the overall gain to apply to the IR file.

• delay The extra delay (in samples) to add to the IR.

• filename The IR to load or create. Possible values are:

• /hilbert creates a hilbert function that can be used to phase shift the signal by
+/-90 degrees. The length will be used as the number of coefficients.

• /dirac creates a Dirac function that can be used as gain.

• A filename to load as the IR. This needs to be a file format supported by sndfile.

• [ filename, ... ] an array of filenames. The file with the closest samplerate match
with the graph samplerate will be used.

• offset The sample offset in the file as the start of the IR.

• length The number of samples to use as the IR.

• channel The channel to use from the file as the IR.

• resample_quality The resample quality in case the IR does not match the graph
samplerate.

Delay
The delay can be used to delay a signal in time.

The delay has an input port 'In' and an output port 'Out'. It also has a 'Delay (s)'
control port. It requires a config section in the node declaration in this format:

filter.graph = {
nodes = [
{
type = builtin
name = ...
label = delay
config = {
"max-delay" = ...
}
control = {
"Delay (s)" = ...
}
...
}
}
...
}

• max-delay the maximum delay in seconds. The 'Delay (s)' parameter will be clamped to
this value.

Invert
The invert plugin can be used to invert the phase of the signal.

It has an input port 'In' and an output port 'Out'.

Clamp
The clamp plugin can be used to clamp samples between min and max values.