The 4Khz upper limit on the low-pass filter...

For the Wahoo™ Dual-Analogue, Digitally-Controlled Wah/Filter Pedal

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kevnull
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Joined: Wed Apr 16, 2014 8:42 pm

The 4Khz upper limit on the low-pass filter...

Post by kevnull »

Due to typical band cat-herding issues tonight was the first time I got to use my Wahoo in a band context, and the upper frequency limit on the Low-pass filter was an issue. :(

Is this a software limitation, or is it the filter circuit itself?

Background: I'm a bass player but I do one live hip-hop band and one dub/electronic/punk band, so I use a lot of effects that add high frequency content (fuzzes, ring mods, sample rate reducers, etc.) and I need to be able to filter a lot of that out but when opening the filter I need it all there. With the Wahoo LPF's upper limit at 4Khz I miss a lot of the upper harmonic content when the filter is 'fully open'.

So is there no way to hear the rest of the signal? Is it always going to be filtered out?
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james
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Re: The 4Khz upper limit on the low-pass filter...

Post by james »

This is a hardware limitation, and it was designed to be that way to allow finest control of the available frequency range. In most cases you never need more than 4kHz. Indeed, guitar amps won't reproduce much above 4kHz anyway. But I can see if you are putting it through a wide-band speaker it could be more of an issue.

You can mix in the dry signal to let the top-end through, but that is is a fixed amount, so you couldn't then close the filter to remove all of the signal.

Using the filter as band-pass will have a gentler rolloff at the top-end. So having one filter set to LP and the other to BP will let more of the high end get through,as the filter closes if the BP filter moves down faster than the LP one you will then retain the LP roll-off for shaping the sound. But this may not be enough for you.
nothim
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Re: The 4Khz upper limit on the low-pass filter...

Post by nothim »

Ugh very frustrating. I'm really missing that 'air' - I've lost most of the fizz from my fuzz. Is the frequency response moddable?
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james
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Re: The 4Khz upper limit on the low-pass filter...

Post by james »

It's not moddable. It's by design -- it's a filter, designed to remove the high end. Guitar speakers don't reproduce much above 4kHz anyway.
nothim
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Re: The 4Khz upper limit on the low-pass filter...

Post by nothim »

Based on the quantity of bass cabs with tweeters, one could estimate that a large number of bassists love to hear frequencies higher than 4kHz.

It's a shame that the frequency range is so frustrating when the pedal has so many other great flexible features. It would be useful for synthy bass sounds if it could go as bright as a real synth cutoff, but then perhaps it's designed more as a wah/auto-wah-pedal-with-extras rather than a synth-filter-as-pedal
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james
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Re: The 4Khz upper limit on the low-pass filter...

Post by james »

Exactly, it was designed to create all of the wah, envelope filter sounds, and similar kinds of things. Of course, we could have made the upper frequency higher, but it would have compromised the lower end, and being able to sweep smoothly down to 10Hz was deemed much more useful (for most users) than sweeping up to the higher frequencies.
flumpjumper
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Re: The 4Khz upper limit on the low-pass filter...

Post by flumpjumper »

It's probably beyond me anyway, but is it possible to mod the filter to give a different range?
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james
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Re: The 4Khz upper limit on the low-pass filter...

Post by james »

It's possible, but not so easy. There are several filter control components that define the filter range. To tell you how to change this, I'd need to run some circuit simulations to work out which components need to be changed and to which values. Unfortunately, I don't have time to do this right now.

I don't think it's too tricky a job if you are able to remove and replace surface mount resistors and capacitors.

If you want to give try, tell me the filter range you need -- I will try to look at this once we get back from the NAMM show (end of January) and see what's possible.
amethystdeceiver
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Re: The 4Khz upper limit on the low-pass filter...

Post by amethystdeceiver »

I'm interested in this too. For me, the 4kHz limit is the most disappointing thing about the Wahoo (the only other one is not being able to control volume w/ the pedal), and I don't even play bass, just guitar. Guitar speakers don't reproduce much above 4Khz, but the loss of air is still very noticeable, especially with a steep LPF and low Q.

I would say 12kHz as the upper limit should be fine.
nothim
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Re: The 4Khz upper limit on the low-pass filter...

Post by nothim »

+1. 12kHz would make me happy too!

Then again, if it could be stretched to 16kHz it could even be used as a full-range synth filter...
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