vca_button->add_events (Gdk::BUTTON_PRESS_MASK|Gdk::BUTTON_RELEASE_MASK);
vca_button->signal_button_release_event().connect (sigc::bind (sigc::mem_fun (*this, &ControlSlaveUI::specific_vca_button_release), vca->number()), false);
vca_button->set_text (PBD::to_string (vca->number(), std::dec));
vca_button->add_events (Gdk::BUTTON_PRESS_MASK|Gdk::BUTTON_RELEASE_MASK);
vca_button->signal_button_release_event().connect (sigc::bind (sigc::mem_fun (*this, &ControlSlaveUI::specific_vca_button_release), vca->number()), false);
vca_button->set_text (PBD::to_string (vca->number(), std::dec));