Author Topic: Two band Parametric EQ  (Read 190 times)

Two band Parametric EQ
« on: April 17, 2019, 01:16:17 PM »
Salutations, all.

My head is spinning these days trying to understand these many options for parametric EQ circuits. These circuits can be various, as I understand from different webpages. Problem is that some give its equations, some do not, and for these I cannot figure its equations, with which I would adapt its components to my EQ's needs.

Before showing these different circuits and their pages I want your advice.

I want to build my two band parametric EQ (band: 50Hz - 2kHz, band: 500Hz - 20kHz, Q: 0.5 - 16, gain: 20dB) with potentiometers for frequency/Q/gain for each band.

How should I do this? Do you already know some solution for this?

Many thanks for your help and time.

MrStab

Re: Two band Parametric EQ
« Reply #1 on: April 17, 2019, 01:29:04 PM »
hi Duderino,

IMO your best choice is a state-variable filter circuit. i make and sell these all the time, thanks to the assistance of people on this forum a few years back.

basic overview here:
http://sound.whsites.net/articles/state-variable.htm

I don't have all the equations with me atm, but if you like i could figure out the component values you need for each parameter you specified, and send them over in a day or 2. if someone wants to jump in sooner, though, go for it!

-g

slacker

Re: Two band Parametric EQ
« Reply #2 on: April 17, 2019, 02:02:10 PM »
There's a relatively simple parametric EQ design here, including formulas for calculating the frequencies and things  http://www.geofex.com/Article_Folders/EQs/paramet.htm

Re: Two band Parametric EQ
« Reply #3 on: April 17, 2019, 03:00:16 PM »
There's a relatively simple parametric EQ design here, including formulas for calculating the frequencies and things  http://www.geofex.com/Article_Folders/EQs/paramet.htm

Thank you, Slacker. I already went through that page and did not fully understand it... That parametric EQ circuit is for two bands, right? And on that paragraph

Quote
Some good places to set the frequency bands for these controls are from about 100 Hz at a minimum up to several kHz. We only get about a 4.5:1 range, so we can pick some values. If we use C1= 0.15uF and C2 = 0.02uF, we get a range of about 100Hz to 450Hz

how did he get those 100Hz? He gave equations with C2 and here where does C1 enter?

MrStab

Re: Two band Parametric EQ
« Reply #4 on: April 17, 2019, 03:50:33 PM »
the gyrator approach, as shown in the Geofex link, is definitely more straightforward to build, but the gain and Q change as the Frequency pot is turned. State-variable uses more parts, but is constant Q and gain.

Re: Two band Parametric EQ
« Reply #5 on: April 17, 2019, 05:08:16 PM »
And I want that...all independent.

But also in your link

basic overview here:
http://sound.whsites.net/articles/state-variable.htm


which I had seen, below Figure 1 he says f0 = 1/(2*π*R*C), which with those components would be 1/(2*π*10000*0.00000001)? This gives 1592.35Hz and he says 159Hz. How is this?

MrStab

Re: Two band Parametric EQ
« Reply #6 on: April 17, 2019, 05:31:58 PM »
i think you have one zero too many in your equation, it should be 0.0000001 farads

Re: Two band Parametric EQ
« Reply #7 on: April 17, 2019, 05:39:21 PM »
Certainly that would solve it, but is that not 100nF (in Figure 1 C=10nF)?

MrStab

Re: Two band Parametric EQ
« Reply #8 on: April 17, 2019, 08:04:16 PM »
ah, i thought you meant Fig 5. yes, i think that is an error.

antonis

Re: Two band Parametric EQ
« Reply #9 on: Yesterday at 05:34:20 AM »
When dealing with too many zeros after decimal point it's more convenient to use micro(μ) & mega(Μ) values in case they're involved in a product..
(e.g. for 16Hz with 100k & 100nF, use 0.1 for resistor & 0.1 for capacitor..)
Can't follow your signature changes, Stephen..!!
but I like what follows:
"put the coffee down, Antonis, and nobody will get hurt."
"Arggg, Jim ...."

ElectricDruid

Re: Two band Parametric EQ
« Reply #10 on: Yesterday at 03:57:22 PM »
the gyrator approach, as shown in the Geofex link, is definitely more straightforward to build, but the gain and Q change as the Frequency pot is turned. State-variable uses more parts, but is constant Q and gain.

Not only that, but the gyrator approach really does only give a fairly limited frequency range, and the OP wanted a 1:40 range. That means a state variable or something else with similar properties is the only option.

antonis

Re: Two band Parametric EQ
« Reply #11 on: Today at 05:48:06 AM »
IMHO, for such a wide frequency spectrum, a 3 band parametric EQ should be more appropriate choice..
(by narrowing range you can be more flexible in Q setting and cap/res values..)
Can't follow your signature changes, Stephen..!!
but I like what follows:
"put the coffee down, Antonis, and nobody will get hurt."
"Arggg, Jim ...."