[Discuss-gnuradio] Fun with filterbanks

[Lisa Creer]

I've recently tried out the synthesis_filterbank method provided in
filterbank.py and received unexpected results. I'm trying to use the
filterbank to create one signal from multiple baseband signals. When I
use two signals to create one output, I can see both signals using the
FFT sink. I can extract both of the channels and replay them (FM
stations). However, when I use three or four input signals, the output
is three or four copies(respectively) of one of the input signals.
What's going on here?

class app_flow_graph(gr.flow_graph):
    def __init__(self, options, args):
        gr.flow_graph.__init__(self)
        self.options = options
        self.args = args

        num_files = args[0]
        samp_rate = args[1]
        logfile   = args[2]
        outfile   = args[3]

        ## Sanity
        print "Num files: %d" % int(num_files)
        print "Outfile:   %s" % outfile
        
        ## Create low pass filter
        taps = gr.firdes.low_pass(1.0, int(samp_rate), 20e3, 10e3, gr.firdes.WIN_HANN)
        print "Len taps: %d" % int(len(taps))

        self.OUT = gr.file_sink(gr.sizeof_gr_complex, outfile)
        self.SYN = synthesize(self, num_files, taps)

        ## Set input file streams
        self.STREAM1 = gr.file_source(gr.sizeof_gr_complex, "nws_25kHz",  0)
        self.STREAM2 = gr.file_source(gr.sizeof_gr_complex, "nws_-50kHz", 0)
        self.STREAM3 = gr.file_source(gr.sizeof_gr_complex, "nws_75kHz",  0)

        ## Connect input to synthesis filterbank
        self.connect(self.STREAM1, (self.SYN, 0))
        self.connect(self.STREAM2, (self.SYN, 1))
        self.connect(self.STREAM3, (self.SYN, 2))

        ## Connect output of filterbank to file
        self.connect(self.SYN, self.OUT)

class synthesize(blks.synthesis_filterbank):
    def __init__(self, fg, num_bins, taps):
        blks.synthesis_filterbank.__init__(self, fg, int(num_bins), taps)

def main():
    usage  = "usage: %prog num_input_files logfile outfile"
    
    parser = OptionParser(option_class=eng_option, usage=usage)

    (options, args) = parser.parse_args()

    if(len(args) < 4):
        parser.print_help()
        sys.exit(1)
        
    fg = app_flow_graph(options, args)

    try:
        fg.run()
    except KeyboardInterrupt:
        pass

if __name__ == "__main__":
    main()