# Low/High cut filter : how does it work?

I have a question about the low-cut and high-cut filter on an equalizer. Let's say, for example, that I'm using a 15 band equalizer with the following central frequencies: 25, 40, 63, 100, 160, 250, 400, 630, 1000, 1600, 2500, 4000, 6300, 10000, 16000.

I read that the first and last bands (25 and 16000 Hz) are low-cut and high-cut filters with -3db at the cut-off value and a slope with -20db per decade.

But, how does it works ?

1. The low/high cut frequencies are 25 and 16000 Hz and for those extreme bands, there is no manual setting : it is automatically set at -3db for the cut-off frequency with a -20db slope per decade.

2. The low/high cut frequencies are at 25 and 16000 Hz and have a "pre-effect" of -3db at the cut-off frequency and a slope at -20db per decade. The user can manually set the cursor, but it means there is a "gap" of -3db between the manual set and the real effet : at 0, there is -3db or correction, at +3, it is 0db, at -3, it is -6db...

3. The low/high cut frequencies are at 25 and 16000 Hz and should be set at -3db but, as the user can manually set the value, it is finally the value set by the user which is applyed at the cut-off frequency with the same -20db per decade slope.

4. Those extrement 25 and 16000 Hz bands are not the low/high cut frequencies but "normal" bands. The low/high cut frequencies are at other values. But, in this case, what are those values for the cut-off frequencies ?

5. Another solution

Please, could you tell me if the way it works is the 1, 2, 3 or 4 ? And if it is another solution, could you explain it to me ?

• Depends on implementation (you should measure the output) and what you can adjust for the filter but, if the cutoff frequency and slope are fixed then are there other options than flat response and these : s33.postimg.cc/a3q7ui8nz/lphp.png – Juha P Jun 19 '18 at 8:58