> We should at least determine where the mismatches are coming from It just dawned on me that the obvious test for ruling out filter approximation error is to type in the given literal coefficients and test only at 48 kHz. Those numbers could always be switched in for the 48kHz case. The filter to use (twice) is then tf2(b0,b1,b2,a1,a2), using numbers entered straight from the spec. The generalized definitions can be used only at other sampling rates.
- Julius On Thu, May 12, 2022 at 11:20 PM <l...@grame.fr> wrote: > Something here to look at possibly ? > > https://x42-plugins.com/x42/x42-meters > > With the source code : > > https://github.com/x42/meters.lv2 > > Stéphane > > > Le 13 mai 2022 à 07:58, Julius Smith <julius.sm...@gmail.com> a écrit : > > > > > Ok, so what I find strange is that the official specs paper does not > specify the exact filter... > > > > I know! That really surprised me as well. The first stage in the spec > (Rec. ITU-R BS.1770-4 5) is clearly a shelf filter, and that could be > specified generically for any sampling rate. Instead they give us a table > of filter coefficients for 48 kHz sampling! They note: "Implementations at > other sampling rates will require different coefficient values, which > should be chosen to provide the same frequency response that the specified > filter provides at 48 kHz". Unfortunately that is not possible! (But it > can be approximated.) We thus have to GUESS the shelf parameters (or > spherical head size and air parameters, etc., if deriving it that way). > The second stage is a simple 2nd-order highpass filter, probably a > Butterworth (the zeros were surely mapped from analog infinity), but again > we only get a table of numbers to guess from. I did note that Butterworth > roll-off was a bit too fast below cutoff, so maybe it's a Bessel filter. > WHY DON'T THEY JUST TELL US? > > > > Zooming out, given this level of extremely simple yet poorly specified > signal processing, and the crudeness of the loudness model itself (see > Zwicker, Moore, Glasberg, Baer, et al. for way better loudness modeling), I > don't take the details as anywhere near "gospel", and I consider my > guesses/approximations so far to be more than adequate. However, I can > also see the value of matching other LUFS meters as closely as possible, > and of course there could be some other bug somewhere that's causing the > discrepancies you are seeing. We should at least determine where the > mismatches are coming from for sure, and if there are no bugs, try to tweak > them out. > > > > Cheers, > > - Julius > > > > > > On Thu, May 12, 2022 at 2:00 PM Klaus Scheuermann <kla...@posteo.de> > wrote: > > Ok, so what I find strange is that the official specs paper does not > > specify the exact filter... > > > > I set up faustlive today with atom as an editor - pretty happy with it > > for now and -double precision works :) > > > > Good night! > > Klaus > > > > On Thu, 2022-05-12 at 13:12 -0700, Julius Smith wrote: > > > I see that the reaper loudness meter is LGPL. Since I require MIT- > > > level license freedom in the Faust world (for my consulting work), I > > > won't look at that. > > > It sounds like we want to tweak the filter designs to give -18 LUFS > > > for the tones you shared from Reaper. > > > The main unknown parameter, as I recall, is the shelf transition > > > frequency, but one could also try to compensate the frequency-warping > > > from the bilinear transform. > > > > > > I compile Faust at the command line, by the way: > > > > > > faust2caqt -double tlufs2.dsp > > > open tlufs2.app > > > > > > - Julius > > > > > > On Thu, May 12, 2022 at 3:14 AM Stéphane Letz <l...@grame.fr> wrote: > > > > > > > > > double precision is not available in faustide, right? > > > > > > > > Yes still not. > > > > > > > > > I will try and > > > > > install faustlive today. > > > > > > > > Yes. You can use « -double » in FL «Compilation / FAUST Compiler > > > > Options » > > > > > > > > > Or would you recommend some other ide > > > > > solution? (I am on arch linux.) > > > > > > > > > > > > > Stéphane > > > > > > > > > > > > > > > > _______________________________________________ > > > > Faudiostream-users mailing list > > > > Faudiostream-users@lists.sourceforge.net > > > > https://lists.sourceforge.net/lists/listinfo/faudiostream-users > > > > > > > > > > > > -- > > > "Anybody who knows all about nothing knows everything" -- Leonard > > > Susskind > > > > > > > > -- > > "Anybody who knows all about nothing knows everything" -- Leonard > Susskind > > -- "Anybody who knows all about nothing knows everything" -- Leonard Susskind
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