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Clipping issue if input 2 is not connected

Zwiebelchen

Fractal Fanatic
Hello everyone.
I'm having a weird clipping issue with my "multi instrument" patch.

I use this method (check the picture attached) to use input 2 L and R and output 2 L and R for two more additional instruments.

It works fine as long all instruments are connected to the inputs and outputs. However, as soon as I unplug the input 2, I get the red out2 clip LED lighting. When checking the output values of output 2 in the utility->status menu, both left and right output 2 are clipping to the max. In addition to that, the CPU usage is only at a constant 88% in my patch, but still I get a CPU warning flashing as soon as this happens. I removed a Reverb in my patch (not listed on the picture); sometimes that removed the clipping issue, sometimes not (which is weird, as the reverb block has nothing to do with this issue at all, as it also happens when there is no reverb in the line!). It seems to be totally random what happens.

Also, this does ONLY happen when you unplug input 2 connections once after powering the Axe. If I reboot the Axe, with no input in input 2 at all, everything is fine. As soon as I plug a guitar cable into input 2 and unplug it again, the issue described above happens. FX-bypassing the lower left VOL block sometimes helps, sometimes not. It's totally weird, I couldn't find a pattern to why this happens.
It seems to be a bug with the AXE-2 that happens as soon as you unplug a cable of input 2 when the AXE2 is powered on.

I don't use AXE-EDIT, so I can not send you a patch. Maybe this description alone is enough to adress this bug. If not, I will get Axe-Edit and try to upload the patch.
 

Attachments

Zwiebelchen

Fractal Fanatic
Okay, its definitely unplugging a cable from input 2 that causes this behaviour. I can reproduce this by 100% in doing so. Also, adding a [GTE] block behind the line seperation fixes this issue magically, so it seems to be a problem with the [SND] and [RTN] blocks creating feedback from noise if there is no cables plugged into input 2?
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
There is a sensor on Input 2. If you unplug the cable from it the FX Loop will not run.
 

Zwiebelchen

Fractal Fanatic
There is a sensor on Input 2. If you unplug the cable from it the FX Loop will not run.
Yeah I noticed that and thought that this was intended.
However, it's still buggy that the loop creates permanent clipping out of nowhere after unplugging a cable from input 2.
If I check the status window, the output bar is completely filled and the clipping LED is lighting despite the input being completely silent.
Maybe this happens because the FXL block then works as a shunt and creates an infinite loop in combination with SND and RTN?
 
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Zwiebelchen

Fractal Fanatic
So is there any chance we can get a toggle für the FXLOOP block that mutes the block out automaticly as soon as there is no cable connected to the input jacks? (in other words: give us an optional switch to decide which behaviour we want for the block - some people might prefer the "works as shunt as soon as nothing is connected" over the mute behaviour)
With the current way it works, this could lead to serious damage of both equipment and ears, as if you don't know about this issue, you will cause an undesired feedback loop... I almost killed my headphones because of that... I was just plain lucky that the volume was turned down by a lot, so that I could avoid a tinitus... but still... this is dangerous in its current state!
 
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Zwiebelchen

Fractal Fanatic
BUMP, since a lot of people seem to use the routing method attached to mimic the copy 1->2 feature without losing input 2 (i.e. for backing track input), this is a big issue again!

It could cause serious damage to ears and equipment and should be fixed ASAP!
 

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GiRa

Power User
It's not a bug, it's your routing: your are creating an infinite loop!

The actual behavior of the FX Loop block is the more flexible, changing it will affect other users.
 

Zwiebelchen

Fractal Fanatic
It's not a bug, it's your routing: your are creating an infinite loop!

The actual behavior of the FX Loop block is the more flexible, changing it will affect other users.
No its not the routing. The routing is totally fine.
As I said:

- it works if all cables are connected
- it works if the cables are not connected when the AXE is powering up

the only situation this does not work is when you UNPLUG a cable after the axe was powered up. It's clearly undesired behaviour and it also happens RANDOMLY, not 100% of the time.


I don't see why the behaviour of the FXL to secretly work like a shunt even when the bypass mode is set to MUTE and there is no cables connected should be any useful for anyone!
 

Rex

Legend!
If you unplug the cable, you're sending the FXL output directly to its input. That's a feedback loop, as GiRa pointed out. Why are SND and RTN in there?
 

Bakerman

Axe-Master
If you unplug the cable, you're sending the FXL output directly to its input. That's a feedback loop, as GiRa pointed out. Why are SND and RTN in there?
They're needed if you want to route something from In 2 to Out 2.
 

Rex

Legend!
They're needed if you want to route something from In 2 to Out 2.
I guess they are, at that. Which could be a bit of a bugaboo in certian configurations.

I'd like to see a couple of freely-placeable inputs and outputs, without any designated effects loop. If you wanted an external loop, you'd create it by I/O placement. I think that would do away with implied feedback loops; you'd know full well if you created one.
 

Zwiebelchen

Fractal Fanatic
If you unplug the cable, you're sending the FXL output directly to its input. That's a feedback loop, as GiRa pointed out. Why are SND and RTN in there?
Yeah, but this behaviour should be dependant on the bypass setting of the FXL block or have a different internal switch for that. If I set the bypass mode to "mute", unplugging the cable should mute the output of the block instead of internally replacing it by a shunt, which is potentially dangerous in a lot of cases.
 

Rex

Legend!
I see what you're getting at, but I don't think unplugging the input is the same as bypassing the block.
 

Zwiebelchen

Fractal Fanatic
I see what you're getting at, but I don't think unplugging the input is the same as bypassing the block.
Still, I think this is a potential danger to both health and equipment, no matter if the auto-routing of Out2 to In2 when there is no cable connected is intended or not.

There should definitely be at least a toggle switch for this (a block-specific switch would be better, though), simply because the above mentioned setup is the only way to create a seperate signal path connecting IN2 and OUT2 or having both inputs active and still being able to use both outputs with different volume controls.
And I think that a lot of people use the method described to achieve this, assuming it is save to do that (as it works fine as long as you don't pull the cable out) and risk damage of both speakers and ears when accidently stepping on or pulling the cable.
 

Rex

Legend!
Still, I think this is a potential danger to both health and equipment, no matter if the auto-routing of Out2 to In2 when there is no cable connected is intended or not.
I think you're right. What do you think of having placeable external ins and outs, and doing away with the FXL block altogether?
 

Zwiebelchen

Fractal Fanatic
I think you're right. What do you think of having placeable external ins and outs, and doing away with the FXL block altogether?
Probably the most elegant solution. But this would still require a setting where unplugging a cable makes the Out signal go back to In or not, depending on what you want to achieve.
 

Rex

Legend!
Probably the most elegant solution. But this would still require a setting where unplugging a cable makes the Out signal go back to In or not, depending on what you want to achieve.
Would it, though? You drop your ins and outs where you want them, and the routing wouldn't change based on what's plugged in. I can't hinl of a situation where I'd add aninput to a preset without intending to use it. And there would be no surprise routings to generate surprise feedback.
 

Zwiebelchen

Fractal Fanatic
Would it, though? You drop your ins and outs where you want them, and the routing wouldn't change based on what's plugged in. I can't hinl of a situation where I'd add aninput to a preset without intending to use it. And there would be no surprise routings to generate surprise feedback.
But then there is no difference to the current way it works. You just save the SND and RTN block for something else.

The only thing that makes the RTN -> FXL -> SND thing dangerous is that the FXL block works as a shunt as soon as no cable is connected.

I can see why Fractal put this in: If you place your FXL as a "true" effects loop in your effects chain, you don't want the signal to get muted as soon as Out2 is not cabled up with In2. However, real AMPs have a switch for that (well, at least my old Marshall had) and I think a "virtual switch" for this would be handy.
 

Zwiebelchen

Fractal Fanatic
Bypass mode will do.
Yes, but this requires user-interaction. What if you accidently step on the cable and it pulls out? This would be devastating, especially in a gig situation. Normally you just hear a loud pop which won't damage anything most of the time, but in this situation you will not only hear the loud pop, but also followed by a permanent sine signal at clipping volume, which is the most damaging noise possible for humans and equipment.
Until you reacted and turned down the volume, you can expect your ears to have taken permanent damage on gig volume.

You can say whatever you want; this issue needs to be adressed, as it's a danger that is not only not listed in the manual (nowhere it says that the FXL block shorts itself internally when there is no cable plugged in), but also does not follow the expected behaviour when applying common sense!
 
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