I’ve been looking into envelope filters for the past couple of years and it’s been more misses than hits (really hard to dial a sound that’s not “mud”). Reviews of the Xerograph are positive - here’s my question: is the Xerograph easy to dial in and get cool sounds easily? Or is it one of these that’s 100% dependent on player style and hard to achieve a nice “quack”/“bow wow”/wah sound?
This is going to be a long post, bear with me, hopefully it can help others.
I'm in early agreement with @jbybj in that you are somehow not triggering the filter to open up, so it remains closed and keeping the high end content from coming out. I have made many mistakes over my time with envelope filters and learned a lot from working with the IE Xerograph Deluxe, which is one of my favorites, if not THE favorite.
You can definitely get a nice quack/wah sound with it.
First things first, are you playing through headphones or through a cabinet? Headphones will make it easier at first to understand what the filter is doing without having the room space create an additional source of variables. If you are in a boomy room you will definitely get mud if the filter is not opening up. So much that you may actually be weary of plucking hard enough to open the filter because you are only hearing the initial mud. My first suggestion is to play through good headphones until you have an idea of the controls of your filter.
Now, let's understand what an envelope filter is doing. I'm going to use a windshield wiper as an example of the envelope filter's action, some use a window shade to describe it, either works.
Imagine a windshield covered in mud. When the windshield wiper is OFF it is on the left and you can't see through the windshield. When the windshield wiper is turned on it goes from left to right and clears away the mud until it reaches the other side leaving you with a clear view. After it gets all the way to the right it returns left again and the mud covers your windshield again. Our envelope filter works like this. In the Off position the high frequencies are filtered out, meaning they are not part of the sound you hear. The tone is dark and muddy. When the envelope filter opens, like a windshield wiper moving from left to right, the high frequencies are introduced and you get back to your original, dry tone. (There are some exceptions depending on if the pedal is automatically cutting some high frequencies but don't worry about that now).
Let's move on and use the controls of the Xerograph Deluxe to see how they affect the windshield wiper (filter). Hopefully this info can carry over to understanding other filter pedals as well.
The Xerograph Deluxe has 6 knobs and 3 switches--RESonance, SENSitivity, FREQuency, Clean, Filter and EXPression KNOBS and Speed, Pole Mode, and Direction toggle switches. Whoa! That's a lot of interaction and potential for mud. No worries, we are going to skip a few. For today let's not worry about the Clean Volume and EXP knobs. Set those all the way counterclockwise. Press the foot switches so that you see a turquoise color, that is for automatic filtering.
Now here's how the rest affect our filter/windshield wiper:
Filter Volume: Set this at noon for our purposes. This just controls the volume of the filtered signal.
Direction switch: Up means the filter sweep (wiper) starts on the left so you only hear low frequencies when you first pluck the note. As the note duration goes on the filter opens up, clearing away the mud as much as you have told it to, which is based on how hard you've plucked. This is the typical quack setting you were asking about. When the volume of your note decreases the filter closes back down to the muddy sound. Down means the filter sweep (wiper) starts on the right so you hear your full signal when you first pluck the note. The filter/wiper actually goes from a clear, brighter sound to a darker one. Remember the mud is reintroduced and then cleared away when the filter returns. For our purposes the rest of my description will refer to when the switch is in the UP position.
FREQuency: This tells us where to start our windshield wiper when it is off. All the way counter clockwise will be very dark since no high frequencies are let through. As you turn the knob clockwise the starting point is higher and the sound is not as dark. (You can see through part of the windshield.) If you have the FREQ knob all the way to the right then the filter is all the way open and there will be no change in sound because there is nothing for the filter to do. The windshield has reached the right side and cleared away the mud so there is no more mud to clear away. I like to set it between 9 and 10 o'clock for the quacky sound. If this is set too low and you are not plucking enough to open the filter you will have a low, muddy sound. So how do make the filter open??? That's next.
SENSitivity: This is one of the most crucial aspects of the filter pedal. Basically, how hard you have to pluck to make the filter open. If you have the sensitivity all the way counter-clockwise you will have to pluck extremely hard to make it open. It is likely the filter won't open at all unless you pull your string like a bow-and-arrow. The windshield wiper stays to the left and you have a muddy window. So, play an open A string and twist the SENS knob until you start to hear the sound change from dark to bright. The wiper blade is starting to move! Great. Try playing soft and hard and everything in between. Where do you feel like you have the most control of the opening and closing? This is different for everybody but I like it around the 3 o'clock position. In the UP mode you'll see on a lot of filters the lines on the Sensitivity and Frequency knobs point at each other. Find your personal sweet spot. If the sound is too bright or snappy then the filter is opening too easily so you need to reduce the sensitivity.
Now that the filter is opening let's bring the quack!
RES sets the amount of quack in your sound. I will admit I'm still learning about what this is doing but basically counter-clockwise is subtle and as you turn the knob clockwise you will hear more quack. With the settings we've dialed in going past noon will start to introduce quackiness. Adjust to taste. All the way clockwise will get you into dangerous ear-piercing or speaker-blowing territory so BE CAREFUL. If your frequency knob is all the way down and RES is up you will be accentuating the low frequencies. So if the filter isn't opening up easily you will have a big muddy rumble. Dial back the RES and raise the FREQ knob. But to answer your question, this knob is what will give you the "nice “quack”/“bow wow”/wah sound".
Pole Mode: 2-pole will give you a wider quacky sound. I found I can usually use more RES in this mode and get a fatter sound. 4-pole will be a bright, sharper sweep, even quackier. 2-pole is like a short, fat wiper blade sweeping a thick amount of mud away at a time and 4-pole is a longer, thinner wiper cutting through the mud more aggressively. Remember, how hard you are attacking your strings have an effect on how the filter interacts. If you pluck really hard in 4-pole mode it can be a very sharp sound because the filter opens to the high frequencies more aggressively. (This is not a perfect description but should give an idea of the differences.)
Speed (S/F switch): Determines how fast the filter opens up or how fast the wiper clears the mud away. Fast will give you the quacky sound and slow will allow for synthy sweeps, more growly, slow wah. Try both and experiment with note duration to hear how the filter is opening and closing with each pluck. In slow mode if you play a long note you can easily hear the filter open and close. Once you hear that, play short notes and see how the filter responds. Does it "quack" with each note or does the sound stay the same? Keep playing and see how your DYNAMICS change the filter's response. Once you can control the opening and closing you are playing the filter instead of the filter playing you!
Finally, if you feel like you've lost any bit of low end you can dial up the CLEAN knob and balance out your sound however you feel. The more clean you introduce, the less prominent/impactful the filtered sound will have.
I really love the XD. If Taylor @Taylor Livingston ever builds an XDD I would like it to have alternate manual control over Attack and Release times and an effects loop like the Chromatron. These would be helpful for additional control over synth sounds. Attack and Release were beyond my initial understanding so the current Speed switch is a great, highly intuitive and useful setup. Also, it would be nice for the EXP knob to allow for setting the maximum frequency without the need for the expression pedal. Of course all of these changes would mean a larger enclosure so there's that.
@Basso Elettrico I hope this helps. I am still learning too so if I've misused any terms hopefully someone can correct me. Cheers!
After having a few filters and having difficulty like you did I decided to spend more time working on understanding the XD than any other envelope filter I've owned so far. My first one was a Q-tron+. I could get a couple good sounds out of it but I remember not being able to control the volume very well. After that I had a new(!) Lovetone Meatball which I really didn't understand and was more frustrated than anything. I sold it and now of course wish I had it to experiment with more. I have a 3Leaf Chromatron which has the separate Attack and Release knobs. These are trickier to dial in than the XD’s two speeds. I actually lent the Chromatron to a fellow TBer to play around with and he has given me some pointers on it and sent some nice clips. I’m excited to try out some new settings when I get it back. Finally I also had the Aguilar Filter Twin. This was perhaps the easiest to get a nice sound but it didn’t feel as responsive as the XD nor provide as much tweakability. I didn’t get as excited playing it. I think this is a good one to start if you don’t have much tinkering time an just want a quacker that works without hassle on a gig. 
