varible LPF/ HPF/Baxandall EQ

[abbey road d enfer]

Yes some authors choose to specify the frequency corresponding to half the max boost or cut. It makes sense  in metrologic terms since it is in the highest slope portion of the curve, but in terms of adequation with the physiological perception it is inadequate.

May be main theory that reference frequency is where the curve get +/-3dB of gain does not work with baxandalls because they have such a wide shelf. And that's  why it's more useful to use irrespective method of calculation frequency.

The notion of using the -3dB point is NOT adequate for filters that don't go asymptotically to -infinity.
The response of a shelf filter is of the type (as+1)/(bs+1); the asymptotes are flat lines, one at a/b, which defines the LF shelf level, and the other at unity.
Serious designers have always recognized this and endeavoured defining a measurement that would be both objective, meaning that could be measured easily, and that would conform to the auditive perception. It has been customary to express the frequency at which the shelf was approached; as a result some would use a point at 1db from the plateau, others would use 3dB from the plateau, and others would use a frequency at which 1/5th (in dB) of the plateau. The latter has the advantage of disambiguating the measurements when the maximum boost/cut is limited to a few db.
Unfortunately, there's never been a standardization of the method.
Now the issue is being complicated by software engineers who apply blindly formulae that they don't even know are not relevant.

 

[brujo]

Nice project! Is there any reason for the filters to be before the baxandall eq instead of after it? Perhaps reversing the order helps reduce noise or subsonic mess when boosting.

Thanks!

 

[JohnRoberts]

Nice project! Is there any reason for the filters to be before the baxandall eq instead of after it? Perhaps reversing the order helps reduce noise or subsonic mess when boosting.

Thanks!

I am not sure what exactly you are referring to this is an old thread, but in general you want to drive the Baxandal section from  a low Z so the filter stage before should provide a low z source.

JR

 

[weiss]

Sorry for bumping the old thread but did someone ever make another batch of pcb's? would be a nice project