erikb1971

possible? Full range high pass & low pass?
« on: September 23, 2011, 02:39:28 PM »
Hi all

For my multi band distortion unit (http://www.groupdiy.com/index.php?topic=45195.0) I am experimenting with different ways to apply distortion to different parts of the audio spectrum. So far, I have been working with a cross over to split the audio signal in three bands. For a lot of reasons, I am not content with the outcomes (http://www.groupdiy.com/index.php?topic=45282.0).
Last night I thought of a new solution. But my guess would be that it is not as simple as it sounds:
I want to basically make 3 copies of the signal. One will be the clear channel. The other three have full range HP & LP filters. With those filters, I can narrow down that full range copy to a small specific range that I want to apply distortion to.

The question is: is it possible to have full range LP & HP filters? I have never seen them outside a DAW, an probably for a good reason.

Thanks for your input!
Cheers

Erik

 
We are getting way past relatively easy


abbey road d enfer

Re: possible? Full range high pass & low pass?
« Reply #1 on: September 23, 2011, 03:30:41 PM »
The question is: is it possible to have full range LP & HP filters? I have never seen them outside a DAW, an probably for a good reason.
It is feasible, but you would have to use range switches. You could have three ranges: 20-200, 200-2k and 2k-20k. In fact, you should allow some overlap, like 20-220, 200-2.2k... Using dual pots, you would have 2nd-order filters (12dB/octave).
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

erikb1971

Re: possible? Full range high pass & low pass?
« Reply #2 on: September 23, 2011, 03:42:54 PM »
Tnx!
hmmm the range switches is more a layout problem than anything else... in my particular case workable... Would a steeper filter require more ganged pots?
We are getting way past relatively easy

abbey road d enfer

Re: possible? Full range high pass & low pass?
« Reply #3 on: September 23, 2011, 05:50:46 PM »
Would a steeper filter require more ganged pots?
Yes. I think you may find quad-gang pots, which would allow 4th-order filters.
Pls note that I gave a strict answer to your question, but some may argue that it may not be the best choice for your intended purpose. For example, a typical narrow parametric EQ, although not offering as good rejection of out-of-band signals, would perhaps have the advantage of having a better recombination. I think some kind of experimentation must be undertaken.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

haima

Re: possible? Full range high pass & low pass?
« Reply #4 on: September 26, 2011, 07:24:57 AM »
maybe use voltage controlled filters? most synth filters cover the entire audio band without range switching or multigang pots, and the resonance controls can be handy to add definition.

check out the synth diy sites - there's heaps of awesome filters to build. if you are going for a distortion/FX box then these might be perfect.

Check out the korg MS20 - it has a HP followed by a LP, like you describe, forming a bandpass response or any variation of hi or low pass.

Also Jurgen Haible's version of  the "wasp" filter has a nice distortion built in.

Really there's hundreds of cool sounding filters in the synth world - and heaps of PCBs available at reasonable prices.

erikb1971

Re: possible? Full range high pass & low pass?
« Reply #5 on: September 26, 2011, 01:12:53 PM »
Yes. I think you may find quad-gang pots, which would allow 4th-order filters.
Pls note that I gave a strict answer to your question, but some may argue that it may not be the best choice for your intended purpose. For example, a typical narrow parametric EQ, although not offering as good rejection of out-of-band signals, would perhaps have the advantage of having a better recombination. I think some kind of experimentation must be undertaken.
ehhh... just to see if I get it... a narrow parametric eq would boost a specified width round a specified freq a certain amount right? but it would leave the other freq intact right?  wouldn't that cause a lot of "unboosted" frequencies to be affected as well by the effects? And wouldn't that undermine the whole idea of just processing specific freq bands? Just in case you have not been able to get through my other posts, I will attach the latest version of my user interface.  Just to maybe get a bit better idea of what I am getting at.
And what do you mean with recombination?

sorry for the late reply btw, notification seems to be disabled
We are getting way past relatively easy

erikb1971

Re: possible? Full range high pass & low pass?
« Reply #6 on: September 26, 2011, 01:35:03 PM »
maybe use voltage controlled filters? most synth filters cover the entire audio band without range switching or multigang pots, and the resonance controls can be handy to add definition.

check out the synth diy sites - there's heaps of awesome filters to build. if you are going for a distortion/FX box then these might be perfect.

Check out the korg MS20 - it has a HP followed by a LP, like you describe, forming a bandpass response or any variation of hi or low pass.

Also Jurgen Haible's version of  the "wasp" filter has a nice distortion built in.

Really there's hundreds of cool sounding filters in the synth world - and heaps of PCBs available at reasonable prices.

I will have to start reading into that subject, because apart from the fact that I loved the filter on the ms10, I have not even a idea what the difference between a normal filter and a voltage controlled filter is! So much to learn!
We are getting way past relatively easy

recnsci

Re: possible? Full range high pass & low pass?
« Reply #7 on: September 28, 2011, 01:06:07 PM »
Problem with full range filters is that you will not have very precise control over frequency. IMveryHo better deal would be switch for three ranges and plain simple Sallen&Key topology.

erikb1971

Re: possible? Full range high pass & low pass?
« Reply #8 on: September 28, 2011, 03:19:52 PM »
Something just dawned on me. After reading lots of pages on filter design I thought: I will NEVER be able to pull this off. So how can I get around it? Incompetence forces creativity.  :D
In my user interface design, I have 3 channels (low f, mid f and high f). Each channel has the possibility to assign any of the three distortion units as an insert effect on that channel. Basically, that already eliminates the need for full range filters. What if I would "hard filter" channel one from 500hz upwards? Then my variable filters would only need to run from 0hz-500hz and from 500hz-0hz. Channel two could be "hard filtered" from 0hz to 350hz and from 2000hz upwards. Then the variable filter for channel two/mid would only only have to run from 350-2000 back and forth. 


Edit: see this is too difficult for me? With the assignable inserts, I just need a normal 4th order lowpass and high pass! Just not full range, both just till a little overlap with the mid band!

So, IF it is possible to have "assignable" inserts on those channels, filtering would be a lot easier... or am I missing out something? 
   
« Last Edit: October 03, 2011, 09:41:40 AM by erikb1971 »
We are getting way past relatively easy

MikeClev

Re: possible? Full range high pass & low pass?
« Reply #9 on: September 29, 2011, 07:24:38 AM »
I wonder...

You have your full range audio input. if you have one Low Pass Filter with full controls producing 0Hz to 'X'Hz.... thats your 'Low f' output.  Then invert the polarity and sum that with your full range input. Would that give you your 'Mid f' and 'High f'  High Pass Filter output? (combined)

Then you could produce your separate Mid f and High f using the same method.

Take your Mid f and High f output from above, run it through your High Pass Filter circuit. There is your 'High f' output. Then invert the polarity and sum that with your 'Mid f' + 'High f' combined output. That should give you your 'Mid f' output.

I hope that makes sense!

-Mike

Edit: I didn't mention why this would be beneficial. It means you don't have to build so many filter circuits, and you don't have to worry about tricky matching of one filter to another when using the frequency controls.
« Last Edit: September 29, 2011, 08:25:00 AM by MikeClev »
Soldering burns: No pain, no gain.

If my opamps can't be discrete, I at least try to keep them discreet.


erikb1971

Re: possible? Full range high pass & low pass?
« Reply #10 on: September 29, 2011, 02:28:39 PM »
smart thinking! If I understand you correctly,  it kind of functions like a 3 way crossover, with two controls. That would mean the mid ban is define by the settings of the high and low bands.  I have experimented with that with a behringer crossover, and was not to please with it. I woul like the possibility of three small bands instead of the full spectrum split into three.... but thanks a lot for the creative thought!
We are getting way past relatively easy

CJ

Re: possible? Full range high pass & low pass?
« Reply #11 on: October 01, 2011, 04:47:41 AM »
filters are pretty involved,

you get a free software download and it will show you things that you did not even think of,

phase shift, response time, resonance  are the basics,

then it gets really freaky,

graphs on parameters that you never heard of,

propagation times, what a snake pit,

anybody know what i'm sayin?

cuz you know i ain't playin

soony boy williamson never used that stuff, and i still listen to his records, jus sayin....

keep it organic,

man, i feel jus like the old cj, rantin about sh*t that i don't understand,

 ;)

« Last Edit: October 01, 2011, 04:50:57 AM by CJ »
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

erikb1971

Re: possible? Full range high pass & low pass?
« Reply #12 on: October 03, 2011, 08:27:07 AM »
yeah .. so eerrmm... eehhh....
(drank maakt meer kapot dan je lief is) :)
We are getting way past relatively easy

Twenty Log

Re: possible? Full range high pass & low pass?
« Reply #13 on: October 03, 2011, 09:33:50 AM »
Sounds like maybe getting into derived/subtractive x-overs...

http://sound.westhost.com/articles/derived-xovers.htm

Maybe not good for PA/speaker systems, but maybe your mileage may vary for FX unit...

erikb1971

Re: possible? Full range high pass & low pass?
« Reply #14 on: October 03, 2011, 09:37:07 AM »
Thank you! I have already read that article,  and experimented with it. The x-over however is not my solution, because the bands are affecting each other (a smaller low band causes a bigger mid band).
We are getting way past relatively easy

clintrubber

Re: possible? Full range high pass & low pass?
« Reply #15 on: October 06, 2011, 04:03:55 AM »
Like CJ said about software: toying around with a plugin in a DAW will learn you a lot about what you actually want - vs what you thought so far you'd be needing (if you haven't done so already).
It'll also show a lot about filter-slopes & their uses. Most synth-filters are 4-pole (24dB/oct) or 2-pole (12dB/oct) but surprisingly the HPF of the MS-20 is just 6dB/oct - and nice at that. The LPF is again 12dB/oct though.

W.r.t multiband-distortion test material, the old Quadrafuzz plugin comes to mind. As you'll know it's the software version of the Craig Anderton PAiA project.

W.r.t. ganged pots, I've seen that at least 4-way pots exist (in Rane crossovers, from Alps I thought). Especially if you need a few of them they might be cost prohibitive for the project.

Bye,

  Peter

erikb1971

Re: possible? Full range high pass & low pass?
« Reply #16 on: October 07, 2011, 06:50:22 AM »
And I thought I already did a lot of testing! :-) I was "back in the lab again"  the past few days. I found an extremely nice vst plugin by DDMF called the IIEQ-pro: http://www.ddmf.eu/product.php?id=0. Just 29$! Nice! With this eq I could test real hp/lp12 hp/lp24 filters... and what do you know:

I need less filters than I thought, and just 2nd order in stead of 4th order! Wow that saved me a buck or two!

Attached is a screen shot of my Cubase test session with the three instances of the IIEQpro. You'll see that for the high and low channels I only use a HPF or a LPF. Both "just" 2nd order. Only the mid section required a double filter, both HP & LP but both still 2n order.
For the high and low channels, using a 4th order filter in stead of a 2nd order made hardly any difference. At the mid channel, using 4th orer filters created a problem: the volume of the "left through" audio was extremely low (the closer the two cut off frequencies were to each other, the lower the volume). So using 2n order filters actually made more sense! 

In general, as you can see, I needed to boost the selected frequency bands a bit by adding a low shelving 10db and a high shelving 3 db at the low and high channels.  In the mid channel I used an "analogue Peak" 10db.

So the mid channel is going to be a bit more tricky, but the low and high channels could do with a relatively simple low and high pass filters. I still have to think a bit about whether the shelving and peak eq's are necessary or  if it would be enough to just boost that channel a bit post eq.

Thanks a lot those in favour of more testing, whether poetical or not :-)
We are getting way past relatively easy


 

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