Haha—yes, I often thought this during online discussions among recording engineers and musicians, when someone has to warn that the shape of EQ filter near Nyquist doesn’t have the response that an analog filter would have, if it’s not done a certain way (and you better check). My thoughts would be, “so…you’re worried someone will put a peaking filter at say 15k Hz or so, with significant boost…uh-huh...and it will not sound the same, in the 20 kHz range, as doing the same thing on an analog console…um, ok…and assuming they could hear it, they would still do it blindly because they could have done it or were used to doing it that way on an analog board?”
Yes, this is why people don’t trust digital. They want to consider doing things that don’t matter or don’t make sense, and compare the results to something that is worse in so many more significant ways… 😂 Not making fun of the effort here, we should always be aware of the results of our choices. And be aware that we might be judged by compromise decisions even when they don’t detract from sound quality, for that matter ;-) > On Dec 5, 2023, at 12:29 AM, Frank Sheeran <[email protected]> wrote: > > Andy Simper said: > > you need to look at the > > frequency response near nyquist and see how closely it matches > > I think that's mathematically true but how much can people actually hear > above 10kHz anyway? Unless they're like under 12 years old and in that case > who cares what their opinion is of the sound? :-D Maybe I just have too > much hearing damage from my years playing reggae keys but when I was doing > software dev in this stuff a decade ago I couldn't really hear the top octave > at all (at age then of 45 or so). > > > > > > On Tue, Dec 5, 2023 at 2:04 PM MUSIC-DSP automatic digest system > <[email protected] <mailto:[email protected]>> wrote: >> There are 2 messages totaling 122 lines in this issue. >> >> Topics of the day: >> >> 1. Simulate simple EQ circuit (2) >> >> ---------------------------------------------------------------------- >> >> Date: Mon, 4 Dec 2023 07:00:47 +0100 >> From: Jens Johansson <[email protected] <mailto:[email protected]>> >> Subject: Re: Simulate simple EQ circuit >> >> I just wanted to say I am awestruck with the amount of good advice so far! >> >> (I have not in any way given up or conceded the fight, just my day job that >> got in between. I do somehow understand how reactances can be seen R --> >> Ljω --> 1/ Cjω and I have some kind of conception about Kirchhoff's and >> Ohm's laws, Euler's formula etc etc, but it's still a bit of DSP stuff to >> absorb beyond this. So I'm ruminating on the issues and reading when I have >> time. I don't have some kind of production deadline, it's a pure hobby >> project ^^ ) >> >> Cheers and much love, >> J >> >> >> > >> >> ------------------------------ >> >> Date: Tue, 5 Dec 2023 08:41:40 +0800 >> From: Andrew Simper <[email protected] <mailto:[email protected]>> >> Subject: Re: Simulate simple EQ circuit >> >> Hi Jens, >> >> It's amazing how complicated such a simple circuit is to solve efficiently >> and accurately, even when kept without any drive (ie linear). It is quite a >> steep dropoff into fairly deep waters, so no worries at all taking your >> time! The good news is that if you really like deep diving you can go down >> a very long way - I still can't see the bottom :) >> >> Even on this EQ there is another layer of complexity that we haven't >> covered yet: "frequency warping". This arises from having a finite sample >> rate, and how the nyquist frequency of 1/2 the sample rate is mapped to >> being a "very large" frequency in reality. So once you have a regular >> Crank-Nicolson / trapezoidal integration via whichever method you want (ie >> nodal, loop, wdf, port theory, laplace + bilinear) you need to look at the >> frequency response near nyquist and see how closely it matches. You can try >> to match either the amplitude (frequency) or phase response more accurately >> at frequencies near nyquist (1/2 the sample rate), but if you match the >> amplitude response closely then the phase response suffers, and vice versa. >> Usually the best "compromise" solution to get both more accurate is x2 >> band-limited upsampling, then match further away from nyquist, then >> decimate /2 (there are no harmonics to limit, so you don't need to >> band-limit before decimation). This process is really a form of >> "oversampling", just without the bandlimiting needed before the decimation >> step, but if you have a non-linear EQ, which is another layer of complexity >> again, you will need the bandlimiting step. >> >> Cheers, >> >> Andy Simper >> >> ------------------------------ >> >> End of MUSIC-DSP Digest - 3 Dec 2023 to 4 Dec 2023 (#2023-67) >> *************************************************************
