A bandpass or notch filter is a high-pass and a low-pass combined together in series. The difference between the two is determined by where the -3dB cutoff frequencies are for the high and low pass filters.
In series will work too depending on design. A graphic EQ does not run each band in series with the next stage/band, they are all in parallel and then summed up. Many amp tone circuits are parallel as well and summed in the next amp stage.
I am smart enough to understand this. :?No, a graphic EQ is a series connection of peaking filters. Peaking filters are not made up of lower-order highpass or lowpass filters. They are (typically) second-order filters with the poles and zeros moving in opposite directions on the root locus as you move the slider.
Actually old analog graphic EQs are not usually implemented as a cascade of second order peaking filters but as a single 2xNth order peaking filter. This is typically implemented by putting N biquads in the feedback path of a "master" op-amp.
It's too complicated to discuss here but it's equivalent to a series cascade of second-order-sections.
Interesting - did we ever get a definitive/authoritative answer to this?
A band reject filter doesn't fit the parameters since it is defined by two frequencies rather than f0, Q, etc. To make a band reject filter put a highpass and lowpass in parallel.
Actually old analog graphic EQs are not usually implemented as a cascade of second order peaking filters but as a single 2xNth order peaking filter. This is typically implemented by putting N biquads in the feedback path of a "master" op-amp.
It's too complicated to discuss here but it's equivalent to a series cascade of second-order-sections.
This I believe: