slackbuilds_ponce/libraries/alsa-plugins

These plugins are used to create virtual devices that can be used like
normal hardware devices but cause extra processing of the sound stream to
take place.  They are used while configuring ALSA in the .asoundrc file.

ffmpeg, speex, jack-audio-connection-kit, and pulseaudio are optional
dependencies.
If you want to build modules for them, you need them installed in advance.