Re: ToneShiftEQ 0.7.0 Released

On Sat, Aug 01, 2026 at 03:51:11AM -1000, robertlazarski wrote:

> The advantage of API eq is it has "proportional Q" that is gain controlled,
> and is one of the reasons it sounds good even with big 12db boosts.

Have a look at
<http://kokkinizita.linuxaudio.org/linuxaudio/paramfilt.html>

All three types work by adding or subtracting the output
of a 2nd order bandpass filter to / from the input.

Type 3 is what you get if the Q factor of that bandpass
is fixed. Very few analog EQs, e.g. the Orban Parasound
outboard ones, used this.

For Type 1, the Q factor is multiplied by the gain (linear, 
not in dB) if that gain is less than 1. 

For Type 2, the Q factor is proportional to the square root
of the linear gain.


Most analog parametrics worked in a different way, similar
to the Baxandall tone control circuit used in mose hifi
equipment. This always produced something similar to Type 2.


For an EQ without Q controls, the difference between the
three options would be significant. If you have a Q control,
each type would just 'feel' different.

Which one would you call 'proportional Q' ?


Ciao,

-- 
FA