Hi Liam, Anish The first tap in the chain is having the most recent taps worth of data being applied to it. We therefore multiply this with the coefficients for the last tap in the FIR chain.
Note that in our pipelines in Simulink data flows from left to right, so that more recent samples are to the left of older ones on the right. In diagrams time is often depicted the other way i.e samples in the past are to the left and future ones are to the right. This may have been a source of confusion. Please see https://github.com/telegraphic/pfb_introduction/blob/master/pfb_introduction.ipynb for a good explanation (and where time is depicted in the same way as it appears in our pipelines). Regards Andrew On Sat, May 17, 2025 at 5:33 PM Anish Roshi <anish.ro...@gmail.com> wrote: > Thanks, Liam, for sharing this. I simulated in Matlab the 'flipped > coefficient' response and compared it with the desired FIR response (see > attached figures). The 'flipped coefficient' implementation works like a > low-pass filter, but with significant degradation > i > > > > > > > > > > > > > > > > > > > > > > > > > > > <https://report.mimecastcybergraph.com?magiclink=https%3A%2F%2Fapi.services.mimecast.com%2Foauth2%2Fauthorize%3Fresponse_type%3Dcode%26client_id%3Do20nRkVXf7VUVnANkXhoOwGytEwGN0YAlyeDJn7oBTGNl2kN%26state%3DeyJhbGciOiJSU0EtT0FFUC0yNTYiLCJlbmMiOiJBMjU2R0NNIn0.pDcrZ3rJzHf3EjHO4TdkbeONSHmyn3SOaye6l0FuY4FAtZJ-CX3JcpKdvN4y-2xCf5BXgBnF6TYpGJPah7YMWIQGHt61LQlszTr6Kj6N9FV-gNeJDqjlhGrPkmFkd9_zOLcpvyx5LzXABDYQ7RP96r--OA6XPuzCGbu4aDQCuuP15Mu_kQelTvO1ERgIXURpoMMiIoCUXy9TsBwdaRxnRX2Dz0A7IVgBpXr-hwoti6H3slgTq6XBBEAA5VjNB-Ez7Qd3GHUf-wLRzXBZJpVZtAjNQ-UGQCJBQtQDxv1H2kYAaiNd74RMcXWhJX09kG1ApikbRmTR-XHTZAJzWlA2Cw.omZNPRhZp0PFcLAt.LrdxF28A5OvV9ij2hSDR8lfayQ1jusEP26aY5yULKG8MuWnB2FItCrTcczBQd3Cu1t0mIsIB3mGpccApGTxqQehWA5n7qjhdOBb1HQ7v7g2jErjtuh9FMaJ1Mt8WYKH_Uu6-W3xgp4E0BDTdver8iU5i7g2ItbKEllzKyjMnZAiAuJnkb2GoPO3ZwerJlVNvvHSnYAyeFezW0b6dzJHg79MokC2Wo8xPXM3YADw_4SmxWB6HmxE0JVc_0cj8tlQOorCoEd_KG8ylkw4qLDId2THNb_bkb4mBN9NxlzcWTMF7IYSjts7fAHlYKdEu6w-v4kw1U3CcDQBqugGzIXAQlBQGA71UhW3JtrStC5AJyLtiR6BYb5BnNDiL5w4gS51bKJ5miXQCJH_6VxTIespespQFTFqrZUKFZt_PFvDYtkmchGXr_zQRlcZStiskNJHbzgS6J4gM-o4f8igAW7lVWcRXSHsxNa2V-0mHrm_ZJsvYMjkzAe5Y9i-UidmqnqhkwVAmMcEE7l0k-0MabipJm8beNyyGPr_-_RwuMudLf1tEiTAGhMy4WDtN5c-y6y-L--y3_XYMwkpUwvxt_rp4EtW7q0tQML8m6ulDkNRLiLTaVZZzsUhV8N0iW9OKc5S2bW1bIH5TLJwy2FHA7YyEuxuAsnnQQVrMmcTehv_YOGc87ZHajb9mQcnvSPkXzbF5Jmm53OSn-0UUJWCCX1ZghHKbL6aAPO8sFk4DId46Hw0zHNJtbfC0jpSvFv0nP7dTi9DaRDVvBedSQMrxSvnuOnenVf0hS7aDRFr19VZBrCpj.fD3WMQIxtzvzRERsTFtx9g%26redirect_uri%3Dhttps%3A%2F%2Freport.mimecastcybergraph.com%2Fcallback> > CGBANNERINDICATOR > > Thanks, Liam, for sharing this. > > I simulated in Matlab the 'flipped coefficient' response and compared it > with the desired FIR response (see attached figures). The 'flipped > coefficient' implementation works like a low-pass filter, but with > significant degradation in stopband rejection. > > If it is indeed a bug, it is better to fix it. I think you should also > discuss this with Mitch. > > Regards > Anish > > On Tue, May 13, 2025 at 6:04 PM Liam Gallagher <liamcgallaghe...@gmail.com> > wrote: > >> Hello Everyone, >> >> Our group is having issues with simulating a PFB, as we are trying to use >> it for channelization and were getting odd behavior on the output of the >> FIR frontend before passing it into the FFT. >> >> Looking into the block construction, it appears that CASPER is inverting >> the order of the coefficients for each all-pass filter tap. >> >> The pfb_coeff_gen block concatenates the coefficients first to last, >> where the first is on the MSB and the last is on the LSB. However, looking >> at the slice block for the first tap, it is slicing the LSB and passing the >> coefficients to the filter backwards. >> >> I did a quick swap of the slice direction, and the resulting simulated >> output was compared against a Matlab simulation of the coefficients calling >> the coefficients of the entire filter (index -1). The resulting plot is >> attached. >> >> Is this a noted bug, or is this an issue of our installation of >> mlib_devel? Any help is greatly appreciated. >> >> Thanks, >> >> Liam Gallagher >> Experimental Astronomy Lab >> Florida Space Institute >> >> -- >> You received this message because you are subscribed to the Google Groups >> "casper@lists.berkeley.edu" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to casper+unsubscr...@lists.berkeley.edu. >> To view this discussion visit >> https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/195c35d1-d096-4abf-a3d2-ce2ea5ea0a70n%40lists.berkeley.edu >> <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/195c35d1-d096-4abf-a3d2-ce2ea5ea0a70n%40lists.berkeley.edu?utm_medium=email&utm_source=footer> >> . >> > -- > You received this message because you are subscribed to the Google Groups " > casper@lists.berkeley.edu" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to casper+unsubscr...@lists.berkeley.edu. > To view this discussion visit > https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAJXWu9usZO9hz4a%3DL5QCXcMV-me3pFY5dyeS3cNO%2BZPLe3aoYA%40mail.gmail.com > <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAJXWu9usZO9hz4a%3DL5QCXcMV-me3pFY5dyeS3cNO%2BZPLe3aoYA%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > Disclaimer The information contained in this communication from the sender is confidential. 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