Help needed on audio band pass filter for spectrum analyzer

[ETC]

I know there is a lot of information already on the web, I finally came upon the color organ project, and assembled 3 filters as per schematic.
The issue here is, I would like to build a 10 band per channel analyzer, and are currently stuck on the filter calculation because the availability for ceramic capacitors is limited (so is my knowledge of bandpass filters), I can get capacitors of the following ratings .001, .0022, .0047, .01, .022, .047, .1, .22 uf. and Resistors I have lots of different values. Does anyone have some sort of calculator to design bandpass filters where I can fiddle with my allowed ratings and make whatever combination of resistors/capacitors to get the desired frequency? and if is not too much to ask, a little enlightenment as to how to choose which frequencies to pick.

 

[ronv]

Here is a calculator.

https://www.wa4dsy.com/robot/bandpass-filter-calc

 

[crutschow]

......................................... Does anyone have some sort of calculator to design bandpass filters where I can fiddle with my allowed ratings and make whatever combination of resistors/capacitors to get the desired frequency? and if is not too much to ask, a little enlightenment as to how to choose which frequencies to pick.

A general active filter calculator is FilterPro available as a free download from Texas Instrument.

The center frequency of the filters in a simple spectrum analyzer are typically done in 1 octave steps e.g. 32Hz, 64Hz, 128Hz, 256Hz, 512Hz, 1024Hz 2048Hz, 4096Hz, 8192Hz, 16384Hz.

 

[ETC]

Thanks a lot ronvr for the calculator link.
Crutschow, I installed FilterPro and looking at it, it looks great, however, there is a couple of questions I'd like to ask you. I can wade into the digital world just fine, but entering the analog arena, I feel really stupid, mainly because I lack a lot of knowledge of the basics I guess. So question is: how much bandpass bandwidth should be the goal when designing? it seems to me like it depends on the frequency being allowed to pass (the higher the frequency, the wider the bandwidth? maybe)perhaps you can point me to a crash course on audio basics ?? before I ask too many stupid questions.

 

[ronsimpson]

Here is a IC with 7 of your filters inside.

 

[ETC]

Hello ronsimpson, i had seen this ic, but decided not to use it because it lacked 3 of the 10 required bands, and also didn't like the multiplexed output. if it all comes to not being able to figure out the filters, that's what I'll use most likely.

 

[ronsimpson]

You can use two parts in parallel.
By changing the RC on the clock pin the frequencies can be moved. By setting one of the parts 1/2 notch up or down you can get 14 frequencies.
My plan involves a small micro computer and a LCD display. I also have driven LEDs from the micro. There is no limit on what the output could be.

 

[crutschow]

........................... I can wade into the digital world just fine, but entering the analog arena, I feel really stupid, mainly because I lack a lot of knowledge of the basics I guess. So question is: how much bandpass bandwidth should be the goal when designing? it seems to me like it depends on the frequency being allowed to pass (the higher the frequency, the wider the bandwidth? maybe)perhaps you can point me to a crash course on audio basics ?? before I ask too many stupid questions.

I would think you want the bandwidth such that the filter response is reasonably down at the edges of the next band. Since each band is one octave apart then you could have the bandwidth for each filter somewhat less than an octave. This means each filter will have a wider bandwidth (in Hz) then the previous (as you go up in frequency) but be comparable from an octave frequency point of view. I would think a two-pole (second-order filter) would be adequate for your needs.

 

[ETC]

Crutschow, yes, that sound right, let me dive into a couple of documents I just found about Q and BW and in case (almost certain) of doubts I'll post them here again. Thanks a lot.