Decimation in FPGA & Decimation in software

In old GNU Radio versions you will find that decim_rate sets how much decimation is done in the FPGA.  

You can of course perform additional decimation in software.  

You'd probably want to use gr.fir_filter_ccf for that job.  The first argument is the decimation rate.

http://gnuradio.org/doc/sphinx/gr/filter_blk.html