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jgaeddert / liquid-dsp

digital signal processing library for software-defined radios
http://liquidsdr.org
MIT License
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Noise generated during decode of Narrow Band FM #162

Open righthalfplane opened 5 years ago

righthalfplane commented 5 years ago

I modified your program to decode Narrow Band FM. I actually sounds quite good - except for the large noise spikes. I have attached the program, IQ file, wav file and the wav file output from another program decoding 10 seconds of the IQ file - it has a minor DC drift problem, but does not show the noise spikes and it has no noise suppression turned on.

Dale.

righthalfplaneNBFM.c.gz 0nbfm_IQ_162390000_50000_fc.wav.gz righthalfplane.wav.gz 0nbfm_IQ_162390000_50000_fc.gz

jgaeddert commented 5 years ago

Are these noise spikes in the RF signal? or in the FM demod output?

righthalfplane commented 5 years ago 
   I am not quite sure - I thought that it may be in the rresamp_crcf_create_kaiser routine. When I do things slightly different using some of your routines (msresamp_crcf_execute and msresamp_rrrf_execute) and some of mine, I do not see it (unfortunately it runs at half the speed of this method).  When changed the bw on the rresamp_crcf_create_kaiser filter to the correct value - it cut the noise in half.