The LADSPA Software Development Kit and the LADSPA plugin API itself are licensed under LGPL version 2.1.
Please note that this is not intended to be the final license for LADSPA. In the long term it is hoped that LADSPA will have a public license that is even less restrictive, so that commercial applications can use it without having to use a derived LGPL library (in a way that still protects the open-source community). It may be that LGPL is already free enough for this, but we aren't sure. Does anyone want to pay for a lawyer? In the meantime, please mail me if this is an issue for you.