Hi Bruce, Thanks for reading codec2.pdf, and your kind comments.
Actually I think you've found an error. For that section I was working back from the source code, sine.c, est_voicing_mbe() function. Looking at the source, the "offset" variable has a negative sign before the "mr" term you suggested in your analysis. Note the source uses different variable names to codec2.pdf, we haven't gotten around to aligning the source code with the document nomenclature yet. I'm travelling at the moment, but will take a closer look when I return home in a week or so. Thanks, David On Thu, 2024-04-18 at 11:19 -0400, Bruce MacKinnon wrote: > Hi: > > What you all are working on is very interesting. Keep up the great > work! > > I greatly appreciate the creation of the detailed description of > codec2 (https://github.com/drowe67/codec2/blob/main/doc/codec2.pdf). > With that document, the code becomes easier to follow. But I have a > question about the math. I’m not that sharp on DSP stuff, so this > may be an obvious question to you all. If this is the wrong place to > ask, feel free to redirect me. > > Page 14, equation 18 makes sense to me - you’re trying to > characterize the relationship between Sw() and W() within each band > of Sw(). And the W*(k - ROUND(mr)) also makes sense, since you need > to remove the “repeating” concept from W() - a spectral copy of W() > is present across the bands of Sw() in the voiced case. It’s like a > modulo w0. > > And the fact that the W* becomes W in equation 19 also makes sense - > real/even in the time domain gives you real in the frequency domain. > > But I can’t figure out how (k - ROUND(mr)) becomes (k + ROUND(mr)) in > equation 19. Certainly W(k - ROUND(mr)) and W(-k + ROUND(mr)) are > the same (even function in frequency domain), but how does W(k - > ROUND(mr)) equal W(k + ROUND(mr))? > > I’m probably missing some property of the FFT that makes this true. > > Thanks in advance, > > Bruce KC1FSZ > > > > > _______________________________________________ > Freetel-codec2 mailing list > Freetel-codec2@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 _______________________________________________ Freetel-codec2 mailing list Freetel-codec2@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freetel-codec2
