Am 01.08.26 um 14:26 schrieb Fons Adriaensen:
On Sat, Aug 01, 2026 at 09:31:18AM +0200, Hermann Meyer wrote:
ToneShiftEQ is a modern 12-band parametric equalizer with APO support,
Some remarks:
Implement State Variable Filter mode (LV2/ stand-alone only)
What is the point of having both biquad and state variable modes ?
Both will produce the same responseif implemented correctly and
given the same parameters. SV has some advantages in real life,
and should be the preferred one.
The actual SV code you use avoids high F,Q instability by using
first order (trapezoidal) integration instead of zero order
(just adding samples). It's a nice idea, but still an approximation.
There is no reason to use this if an exact solution is available.
See <http://kokkinizita.linuxaudio.org/papers/digsvfilt.pdf>.
This is actually used in zita-eq1.
Show accurate Filter-curves in Biquad mode
Except they are not, also not in SV mode.
Try this two parametrics (in SV or BQ mode):
500 Hz, -30 dB, Q = 10
1000 Hz, -30 dB, Q = 10
The measured response shows -4.5 dB halfway between
the two dips (at 710 Hz). Toneshift shows something
close to -14 dB (difficult to read exactly). Also
the individual responses of the two filters are wrong.
Errors are smaller for less extreme settings, but that's
no excuse.
Which tool do you use to measure that?
ToneShiftEQ use the same response calculations for the UI and the dsp,
https://github.com/brummer10/ToneShiftEQ/blob/main/EQ12/IRMatch/BiquadResponse.h
https://github.com/brummer10/ToneShiftEQ/blob/main/EQ12/IRMatch/SVFResponse.h
APO support.
This 'Equaliser APO' [1] seems to be one of the most hyped
things in Windows audio circles. It has 15 or 31 parametric
bands. There are entire websites and GIT repositories
offering presets for this thing, each one 'professionally
optimised' for one particular type of music or 'mood'. As
if that would make sense. It's hard to find more refined
pure liquid BS. Which one should I used when listening to
'reggae' while in a 'worship' mood ? Both in series ?
There are also profiles out there for speakers and headphones.
* Some more general musings - not related to ToneShiftEQ in
particular.
Why do 'modern' equalisers need that many sections ?
I could answer that question, but most readers here
won't like it, so I'll shut up.
You could still disable any Band you don't need and use just 4 or 3 bands.
Why do the GUIs of 'modern' equalisers look like the
dashboard of a cheap Chinese E-car instead of being
a bit more functional and ergonomic ? Same answer.
That is my taste, I like it this way. Sure, it wont be anyone's darling,
but, for me it looks nice and gives me the information I need.
The famous big analog mixing consoles from last century
(Neve, SSL, Harrison, Cadac, Midas, MCI, ...) typically
had 3 or 4 section EQ. Some of them just had a choice of
3 frequencies for each band and fixed Q. Still these were
used to produce some of the most magnificent music recordings
in history. Of course no FR display, sound engineers didn't
need it, they just listened.
I remember using Neve, Harrison and SSL, but don't recall
ever needing more than 3 sections.
[1] APO means 'Audio Process Object', sort of a plugin
standard for the Windows 'system audio' chain. Then why
is 'Equaliser APO' used as the actual name of one particular
EQ ?
However, please let me know which tools you use for your measurements,
I'll try to reproduce it and find the culprit to fix it.
