Toolame is an open source implementation of MPEG-1/2 Layer II audio coding.
It supports also options to add DAB PAD field on every frame.
Source code: http://sourceforge.net/projects/toolame/files/
A more recent fork called twolame exists. Despite de fact that the code has been cleaned, twolame has lost DAB support that was present in toolame. So be careful to install toolame and not twolame for DAB tests.