SergeModular

Hey all,

I’m trying to get my head around what the X Fader can and can’t do. According to the module info, if I have two audio signals plugged into it, then as one signal fades in volume, the other should increase. But I’m having trouble finding a patch that will demonstrate this. Instead I find that both signals fade or get louder together.

For example, on the Creature, I patched the left-hand TGO sawtooth to XFAD input 1, and the right-hand TGO triangle to XFAD input 2, and I LFO modulated the amplitude of input 1. I would expect the input 2 signal to grow stronger and weaker as the input 1 signal modulates. But I only hear the input 1 signal modulating while the input 2 signal stays static.

Also, the X FADE knob doesn’t do what I would expect either. My expectation was that since the label reads “1 XFADE 2”, then if the knob was all the way to the left you’d only hear input 1, if the knob was all the way to the right you’d only hear input 2, and if it was in the center you’d hear each equally. Instead, I hear both signals at full strength full-left or full-right, and nothing at all at dead-center. The only difference between hard-left and hard-right (as viewed on my oscilloscope) is that one is the inverted combined waveform of the other.

Lastly, an LFO applied to the VC XFADE jack alternates between hard-left and hard-right (with full input 1 and input 2 signal strength with each swing). And an LFO applied to the VC GAIN jack modulates the amplitude of the combined signals.

At the very least, I thought the X FAD module would be like a two input mixer, but that doesn’t seem to be right either.

So thus far, I seem unable to get any true cross-fading happening between input 1 and input 2. Perhaps I’m not getting what “equal-power cross fade unit” means? Can someone help me understand this module better?

Thanks!

ty

________________
http://sublevel9.net

Hi Bakis,

Thanks for replying! Regarding your statement: “with no input on the vcxfade input, indeed you should only hear input 1 on the fully left setting of the xfade knob and input 2 on the fully right.” Would you mind double-checking that for me? That’s definitely not the result I get. Here’s a simple test I just now ran to double-check this:

1 – Insert a sawtooth at Input 1
2 – Insert a second sawtooth an octave higher at Input 2 (the octave difference helps to hear both signals)
3 – Insert a single output cable to audio path
4 – With nothing else plugged in to the XFAD module, turn XFADE knob full left (observe on scope)
5 – Turn XFADE knob full right (observe on scope)
6 – Turn XFADE knob to center position (hear anything?)

What I observed at step 4 (XFADE knob full left) was I could hear both sawtooth waves at full strength, and the scope confirmed the positive polarity. At step 5 (full right) I could again hear both signals at full strength, and the scope confirmed inverse polarity (i.e. the sawtooth waves now looked like ramp waves). At step 6 (center position) I hear nothing. Is that how it’s supposed to work? If yes, how is this useful, other than inverting polarity of the XFAD output?


For the next steps I introduced a triangle LFO to the patch:
7 – Apply LFO to the VC GAIN jack, and turn XFADE knob full left (observe on scope)
8 – Turn XFADE knob full right (observe on scope)
9 – Turn XFADE knob to center position (hear anything?)

Here’s what I observed:
* At step 7, when the LFO goes positive both signals fade in/out at full strength (positive polarity – i.e. sawtooth)
* At step 8, when the LFO goes positive both signals fade in/out at full strength (negative polarity – i.e. ramp)
* At step 9, when the LFO goes positive both signals fade in/out barely audibly


Final steps:
10 – Remove LFO from VC GAIN jack and apply it to the XFADE jack
11 – Turn XFADE knob full left (observe on scope)
12 – Turn XFADE knob full right (observe on scope)
13 – Turn XFADE knob to center position (observe on scope)

Here’s what I observed:
* At step 11, both signals modulate at full strength, with positive side of LFO holding longer
* At step 12, both signals modulate at full strength, with negative side of LFO holding longer
* At step 13, both signals modulate at full strength, with equal time on positive and negative sides of LFO


If these are the expected results, it seems that the XFAD module is capable of cross-fading between positive and negative outputs (both signals at full-strength in either case), but otherwise behaves as a straight-forward 2-input VCA. But I don’t think that’s how it’s supposed to work. Here’s the description from the catalog:

“The CROSS-FADER (XFAD) is an equal-power cross fade unit. The module has two signal inputs. As one signal increases in level at the output under manual or voltage control, the other signal decreases in level at the output. This effect is used to accurately fade one sound in while fading another out. Cross-fading with voltage control permits a smooth transformation between two different timbres. If a sound and its reverberated image (available with the Wilson Analog Delay) are sent through the cross-fader, the reverb mix can be voltage controlled. This effect can be used to modify the spatial characteristics of a sound event, from immediate presence to distant ambience. In addition to the cross-fade function, a VCA controls the output amplitude.”

I’m not seeing the behavior described in the statements regarding fading one signal out while the other fades in. Can you suggest a patch where I should see the correct cross-fading behavior? Or does it sound like there’s a problem with my XFAD module?

Thanks!
ty

________________
http://sublevel9.net

Thanks for the feedback, guys. I have a phone “date” with Rex in the morning. I’ll let you know how it turns out.

ty