Stereo Q Filter WANTED!

[keko]

Hi guys...i was driving the other day, and suddenly one of my car speakers turned off, so I ended up listening through a mid-range speaker to the left, and just a tweeter to the right....so that got me thinking (it's cool when you get that state of mind  :wink: )

How would someone go to make a stereo wahwah, Dr. Q or so in a way that the modulation is biased into either side?

My first idea would be:

1. get the effect you want to tweak
2. split the output into two channels
3. use a high-pass filter on one side, low-pass on the other.

Is there a more efficient way? Would this even work?

Thanks for your input

[Peter Snowberg]

That's the way I would do it.

The options are almost endless.... you could fuzz only one, or fuzz both differently, or you could process each in a totally different way.

I would suggest using steep filters so you get the largest separation.

Experiment away!

Take care,
-Peter

[keko]

Cool!! thanks Peter.

By steep filter you mean those with huge difference in the waveform's frequence? or is that a special kind of filter?......mmm my language skills are leaving me behind. :?

[Peter Snowberg]

I'm sorry I should have been more specific.

Your language skills are fine. I often make the mistake of not appreciating that so many people here speak two or more languages.

By "steep" filter, I mean one that cuts off very quickly as you reach the filter frequency. As you get more and more complex with the filter, the "steepness" of the filtering goes up. A single stage filter has a cut or boost of 6dB per octave. Two stage filters (also called 2nd order filters) cut or boost at 12dB per octave. 3rd order filters cut or boost at 18dB per octave.

This link has the design of an 18dB per octave electronic crossover:
http://sound.westhost.com/project08.htm

The only problem is that it is centered around 300Hz because it's made for speakers. If you double the frequency setting resistors and cut the capacitor values in half, you will double the frequency. These parts are all marked with a *.

More general information here:
http://home.online.no/~jaeioluf/sound/eqpassiv.htm#HPF

A better approach would be to use a pair of tuneable filters or a different style of filter so that you could vary the frequency. Try looking for "state variable" filters like you find at the heart of the Mutron III That will give you LP, HP and BP at all at once with a very simple circuit and you can modulate the frequency as part of the effect too.

Take care,
-Peter

[Paul Perry (Frostwave)]

I've always wanted an effect where the delay varies with frequency. I suppose having a slightly different delay on one half will have to do..

[smoguzbenjamin]

I thought of this at school today...
How about a wah pedal that sweeps up on one channel, and down on the other. That would sound really cool...

[Brett Clark]

you can use a State Variable Filter, which will give you complementary outputs (high-pass and low-pass) at the same time

[Mark Hammer]

The E-H Baseballs incorporates two Dr.Q-type bandpass filters and a single envelope follower driving each.  The idea is to have a thicker sound than a stock DQ would deliver by shifting a broader range of emphasized frequencies at once with the twop staggered-frequency filters.

On my Baseballs clone pedal, I installed a "split" switch that routes one of the swept filters to a second output jack rather than to the passive mixer junction.  

The neat thing is that since you can twiddle the start point of the sweep for each filter section with the stock trimpot, you can adjust the degree of left/right stagger with respect to sweep.

I should try and make a sound-clip of it, since to be honest I have never actually heard the thing in stereo.  So far, I have only used the dual outs to pick one filter or the other, which is another thing the split function lets you do.

[keko]

though I havo absolutely NO clue about how to pursue my objective, I found this link. I think it will be usefull for those of you who really understand how this stuff works.

I'll start reading too, and maybe come up with a mixed schematic (effect plus SVF) that later you might help me correct / improve.

Educational Link:
http://www.uwm.edu/People/msw/StateVariable/

'Grab your protoboard and build' Link
This one seems really easy to implement over any effect. As far as I understand, you could just attach this to the output of any effect? That simple? Parts seem to be common too.
http://home.swipnet.se/cfmd/synths/schematics/svf1.pdf

THANK YOU!!!!
.....the only bad thing about this forum is that I spend most of the time in it at work...and work doesn't get done by itself....life's tough. (well, that's my problem, not the forum's)

[Paul Perry (Frostwave)]

smoguzbenjamin, your 'one up and one down' wah has been done, the most notable version being a mechanically linked pair.
You could also use a stereo pot, and wire one backwrds (providing the pots were linear) and duplicate the circuit.

[smoguzbenjamin]

It's time to get a wah casing then :twisted: