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 Hi Henry, Look up the Discrete Fourier Transform in its Matrix form: You take a vector of samples and multiply it with a matrix to get the discrete Fourier transform of , which I shall denote : , with (i.e. a square matrix, representing the N-point DFT) (i.e. column vectors). Remember how you do matrix-vector multiplication: To get the result's element in its $n$-th result row and the $m$-th result column, you take row $n$ from the left factor (i.e. a row of $W$, which has $N$ rows, so $n\in\{1,\dots,N\}$), and multiply it point-wise with $m$-th column of the right factor ($x$, which only has 1 column, so $m\equiv 1$) and calculate the sum. On 20.03.2016 17:45, Henry Barton wrote: So correlating is digitally mixing something with a predetermined sequence? I’ve been struggling to figure out what correlation means and this seems right. I guess, then, if you have a PSK waveform you might multiply it by something, starting at various offsets in the signal, to try and decode it? Sent from Windows Mail From: madengr Sent: ‎Sunday‎, ‎March‎ ‎20‎, ‎2016 ‎12‎:‎22‎ ‎PM To: address@hidden Yes, pretty much.  With the DFT (and the continuous one) you are correlating the input waveform with harmonically related, complex sinusoids; essentially for each harmonic you mix it down to DC then sum (integrate).  The FFT is different (I actually don't know how it works, other than it operates on 2^n samples), but the output is the same. Lou Henry Barton wrote > I’ve read up on the FFT and DSP and I must say I’m impressed that > multiplying two waveforms is the digital equivalent of heterodyning. Am I > right in my understanding that finding frequency components (FFT-ing) is > simply multiplying a series of known sine waves by your input waveform? -- View this message in context: http://gnuradio.4.n7.nabble.com/Handling-of-IQ-files-tp58915p58935.html Sent from the GnuRadio mailing list archive at Nabble.com. _______________________________________________ Discuss-gnuradio mailing list address@hidden https://lists.gnu.org/mailman/listinfo/discuss-gnuradio _______________________________________________ Discuss-gnuradio mailing list address@hidden https://lists.gnu.org/mailman/listinfo/discuss-gnuradio