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[Discuss-gnuradio] Reducing the samples from ADC

From: pratik hetamsaria
Subject: [Discuss-gnuradio] Reducing the samples from ADC
Date: Wed, 11 Jul 2007 17:01:48 +0100 (BST)

i am working on tx_voice.py and rx_voice.py. I have to capture data directly from usrp and write onto a file and process that. The problem is that the file which is made by the data coming from usrp is very big so basically i am not able to process that. Is there any way by which i can reduce the size of the file without affecting my audio quality much.

The rates which i am presently using on the tx_voice.py are:
Bitrate- 50,000
samples per symbol - 5
interpolation - 512

Rates which i am using on the rx_voice.py are:
Bitrate- 50,000
samples per symbol - 5
decimation - 256.

Moreover, i have tried using gr.fir_filter_ccf (for decimatio in software)in the following fashion

        chan_coeffs = gr.firdes.low_pass (1.0,                  # gain
                                          self._samples_per_symbol, #     sampling rate
                                          1.0,                  # midpoint of trans. band
                                          0.1,                  # width of trans. band
                                          gr.firdes.WIN_HANN)   # filter type

        self.chan_filt = gr.fir_filter_ccc(sw_decim, chan_coeffs)

and making a connection as
    fg.connect(self.u,  self.chan_filt, self.packet_receiver)

where destination refers to the file onto which i want to write.Now, this works fine as long as sw_decim =1. But, if i change the value to 2,4 ,8 or any other then i dont receive any packet. The file size does change as required (i am able to observe that as the usrp is always sending data). what i have understood is that because of the decimation i am missing samples and thus not able to receive packets.So, can somebody please explain how to get around the situation.

Thanks for all the help.
Pratik Hetamsaria


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