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Re: [Discuss-gnuradio] Off-line signal processing (GR in slow motion)

From: Monahan-Mitchell, Tim
Subject: Re: [Discuss-gnuradio] Off-line signal processing (GR in slow motion)
Date: Thu, 29 Aug 2013 15:53:46 +0000

>> Off-line example (3 separate flowgraphs, run one at a time):
>> 1. USRP --> File
>> 2. File --> AM Radio Demodulation, produces audio data --> File
>> 3. File --> Throttle @ audio rate --> Audio Sink

As Tim O pointed out, #3 would just be File --> Audio Sink, since the Audio 
Sink consumes at a fixed rate.

>> Note that #2 can take as long as needed to complete, no issues with loss of 
>> data.
>> If so, how would I set up flowgraph #2 above?

> Hm, I'm not quite sure if I understand your problem. You can simply connect a 
> file source to the am demod and then to a file sink.

Yes, #2 was meant to depict whatever processing blocks are needed to go from RF 
samples to audio samples.

>> This flowgraph will then run unlimited ('cause no throttle). But that's OK 
>> if the input file is limited in size. Your CPU will be running full power 
>> until there's nothing left to process.

Yes, I understand that part. What I was not sure about was whether the real 
time rate of data passing through the system was required to be able to do 
proper signal processing? Or whether some of the processing blocks are simply 
told what the rate is?

Here is another example: suppose I have a file of audio samples. To determine 
the spectrum of the data , isn't the sampling rate of the data a factor? Or 
must a scalar be applied somewhere (related to the sampling rate) to convert 
relative values to energy per Hz?

If the latter is true, then I'm still unclear on whether something like the 
rx_ofdm example under gr-digital can work, just given a file of samples and no 
throttle block (CPU limitations aside)?

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