Some examples of those PipeWire modules are the Filter-Chain module, which constructs a “pipeline” filter from a chain of other filters: Both third party filters from other projects such as LADSPA or LV2; built-in PipeWire filters (equalizers, spatializers, mixers, etc...); the Echo-Cancel module which cancels echo from capturing devices by monitoring their respective playback device; and even the Loopback module which does nothing but forward the audio signal as it is, without changing any of its frequencies... this one is mostly useful when the user wants to hide a specific device.