What is the output sample rate of the below given code?

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Shubham Singh 2023-7-28

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评论： Shubham Singh 2023-8-1

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Daniel 2023-7-28

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Per the comments, the output sample rate is 4800, but the more important question would be what the upsampling ratio is.

The rctFilt object upsamples the input by a factor of sampsPerSym, which is 4.
The d2 object upsamples that by a factor of the first argument, which is 2.

Between those two stages you get an upsampling factor of 8, so the output frequency is 8x the input frequency.

The output is then truncated to the same length as the input, which corresponds to 1/8 of the timespan represented by the input.

That looks similar to what I see when I plot the spectrum with plot(20*log10(abs(fftshift(fft(y))))). The peaks are a little clearer when you plot in magnitude than when you plot in dB. Since the signal appears to be using the full spectrum and it's flat across the spectrum, you don't get a very obvious delineation between frequency peaks. I'm fairly sure this is by design, though I'm not specifically familiar with C4FM.

Shubham Singh 2023-8-1