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Not a Bug Digital clipping

littlebigfis

Inspired
Patzag, by any chance do you have another recording interface, along with your AXE II usb, plugged into your mac? If so, you may want to try removing the Axe II usb for a quick test. I find, in logic 9 even when i have selected my other interface in preferences, in my case an RME Fireface 800, logic still holds on to the AXE II even though the preferences tab indicates RME Fireface. With input monitoring enabled i get swirling echoes and/or major distortion. I have to completely remove the USB cable from the Axe II to eliminate the weirdness.
 

Patzag

Fractal Fanatic
Patzag, by any chance do you have another recording interface, along with your AXE II usb, plugged into your mac? If so, you may want to try removing the Axe II usb for a quick test. I find, in logic 9 even when i have selected my other interface in preferences, in my case an RME Fireface 800, logic still holds on to the AXE II even though the preferences tab indicates RME Fireface. With input monitoring enabled i get swirling echoes and/or major distortion. I have to completely remove the USB cable from the Axe II to eliminate the weirdness.
Thanks for your interest. No. I have no other interface connected to the Mac. The clipping occurs whether direct out to Audio or USB to the Mac. Disconnecting the USB entirely makes no difference in the sound.
 

javajunkie

Moderator
Moderator
Okay,

I was able to recreate this and eliminate it. If I took that patch simplified it by taking out post effects (besides a volume block which I placed where the lopper is) and turned up the amp block while compensating by turning down the vol block level I got clipping with no clipping light.

If I took the feedback send and return out and kept everything else the same the clipping stopped.
 

MisterE

Power User
So, If I understand this correctly, the amp can clip the send & return blocks.
I always set my amp and cab volumes to the level when I bypass these blocks.
I suppose this is a good way to avoid clipping and setting overall levels because the bypass level serves as a reference point.
 

javajunkie

Moderator
Moderator
So, If I understand this correctly, the amp can clip the send & return blocks.
I always set my amp and cab volumes to the level when I bypass these blocks.
I suppose this is a good way to avoid clipping and setting overall levels because the bypass level serves as a reference point.
Its not the amp. You could probably do it with any block. I don't know if it is clipping the send or returns. we don't have enpough information for that. But cliff can look into and see what he come up with.

I was just able to recreate the issue and point to an area that seem to eliminate it.
 
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FractalAudio

Administrator
Fractal Audio Systems
Moderator
The feedback return will clip at extremely high input levels. This is a protection mechanism to prevent against "runaway" if someone creates a feedback loop. The feedback return clips at a level of 38 dBu. This is nearly 10 times the maximum output level of the unit. If this protection were not there a feedback loop could be created that would result in digital overflow and cause a reboot.

If you really try, yes you can create clipping. However, no one should encounter clipping with "sane" parameter values.

You guys need to let this go. Trust me, there is no bug that is causing clipping under normal operation. Sure, if you want to dial in crazy values you can clip something, but if you use the unit as intended, you cannot.
 

Patzag

Fractal Fanatic
Okay,

I was able to recreate this and eliminate it. If I took that patch simplified it by taking out post effects (besides a volume block which I placed where the lopper is) and turned up the amp block while compensating by turning down the vol block level I got clipping with no clipping light.

If I took the feedback send and return out and kept everything else the same the clipping stopped.
The feedback return will clip at extremely high input levels. This is a protection mechanism to prevent against "runaway" if someone creates a feedback loop. The feedback return clips at a level of 38 dBu. This is nearly 10 times the maximum output level of the unit. If this protection were not there a feedback loop could be created that would result in digital overflow and cause a reboot.

If you really try, yes you can create clipping. However, no one should encounter clipping with "sane" parameter values.

You guys need to let this go. Trust me, there is no bug that is causing clipping under normal operation. Sure, if you want to dial in crazy values you can clip something, but if you use the unit as intended, you cannot.
Thanks Sean & Cliff. I did the same yesterday night. I tried a number of presets and was unable to recreate the clipping, except where I had a Send/Return loop. I removed the send/return and it handled the issue. I just didn't get a chance to post until now.

I'm cool with that. I know what causes it and how to avoid it, I have no issue with it.
 
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Patzag

Fractal Fanatic
I'm trying to imagine a preset where I've set the amp (or any block) to output 38dBu. Holy crap Batman!
You can't. The maximum level is +20 dB on the level parameter of the amp. But by the time you do that, the processor craps out and reboots automatically! Yuk!!
 

steadystate

Fractal Fanatic
The level parameter is not an indication of the output level of the amp block. The amp block can provide massive gain even when the level parameter is set to 0 dB, especially with high master volume levels. You can easily exceed 38 dB of gain. In this case, a subsequent block would need to attenuate the signal to prevent the output LEDs from illuminating. As Cliff said, even though the feedback block has an amplitude limit of over ten times the output stage, the other blocks can handle an even stronger signal.

FWIW, I generally set the level parameter of high gain amps around -20 dB to make the engaged level on a par with the bypassed level. I can't think of a single instance where my high gain amp block levels are not cut significantly compared to cleaner amp blocks.
 

javajunkie

Moderator
Moderator
The level parameter is not an indication of the output level of the amp block. The amp block can provide massive gain even when the level parameter is set to 0 dB, especially with high master volume levels. You can easily exceed 38 dB of gain. In this case, a subsequent block would need to attenuate the signal to prevent the output LEDs from illuminating. As Cliff said, even though the feedback block has an amplitude limit of over ten times the output stage, the other blocks can handle an even stronger signal.

FWIW, I generally set the level parameter of high gain amps around -20 dB to make the engaged level on a par with the bypassed level. I can't think of a single instance where my high gain amp block levels are not cut significantly compared to cleaner amp blocks.
Exactly - you have the gain from what ever is in front of the amp (if it adds gain), the preamp gain, the power amp gain, and level parameter.
 

MisterE

Power User
So as I said earlier, setting the level of the amp block to the bypass level is good practice?
I've always done it this way but it seems a lot of people are struggling with their levels.
 

Patzag

Fractal Fanatic
FWIW, I generally set the level parameter of high gain amps around -20 dB to make the engaged level on a par with the bypassed level. I can't think of a single instance where my high gain amp block levels are not cut significantly compared to cleaner amp blocks.
This is a fascinating note: Are you saying that when you play with the amp block bypassed, you have approximately the same level as with the amp block turned on?
 

yek

Moderator
Moderator
This is a fascinating note: Are you saying that when you play with the amp block bypassed, you have approximately the same level as with the amp block turned on?
In my case: yes. The Amp block in my Cameron preset for ex. is around -22dB. This way it is as loud as my clean preset (by ear). And I've taken care that my clean preset doesn't clip the digital signal, even when its lead boost is On. The overal level of the Cameron preset is - by ear - about the same as when the Axe-Fx is is Bypass mode.
It's so easy to prevent presets from clipping by keeping the level down. Adjusting Amp level doesn't affect the tone in any way.
 

steadystate

Fractal Fanatic
This is a fascinating note: Are you saying that when you play with the amp block bypassed, you have approximately the same level as with the amp block turned on?
Generally, yes. My reference level for all presets is a row of shunts passing a completely unprocessed guitar (for the largest possible crest factor). In my presets, I try to keep all blocks other than the amp at unity (unless they are for a boost function for solos, etc.). After setting the drive and master volume for taste, I then use the amp level to match the level of my presets to the shunt preset. Using this method, there is no way I can ever achieve internal clipping, the SNR is great, and clean/dynamic tones can still be adjusted to compete with (or exceed) the level of distorted/compressed tones.

If I cranked the level of high gain amps to just below clipping of the output stage (or way beyond the level of an undistorted/uncompressed tone), I'd never be able to adjust the level of clean uncompressed tones to match them without clipping the output. You basically have to run high gain amps at a lower level unless you never intend to use cleaner tones.

I should clarify my previous posts by saying that I generally drastically reduce the level of higher gain amps that require a high master volume level, not necessarily high gain amps that don't rely on power amp distortion and sound best with low MV settings. I don't believe I have any amp blocks that aren't cut in level to some degree. Considering how much gain can be obtained from the amp block, the fact that this hasn't been posted until now shows how much headroom the internal processing handles. I think the limiting of the feedback block is the only reason it was noticed at all.
 
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jimfist

Fractal Fanatic
This is a fascinating note: Are you saying that when you play with the amp block bypassed, you have approximately the same level as with the amp block turned on?
I concur with yek, steadystate, et al....proper gain staging of blocks in comparison to bypass state (global, block, or shunt-only preset) is a good practice IMO, of not THE most technically sound method of creating presets. Getting to the edge without going over can be a challenge with a block heavy preset.
 

Patzag

Fractal Fanatic
All right, so I tried this: Bypass the Axe entirely and plugged my guitar in. The output level is so low, that it won'd get any significant level out of my powered speaker. Obviously I can hear it, but not enough for even a bedroom gig!
So how am I supposed to match that level to the level of my presets? I must be missing something in your directions, Steadystate. Even bypassing only the amp block does not drive my speaker enough for gig level.
 

jimfist

Fractal Fanatic
hmmm...I would expect reduced level for sure, but not to the point you describe. Please refresh our memory (apologies if you've already posted this): what is your guitar and what are the speakers you're using? Are you using the XLR outputs?
 

yek

Moderator
Moderator
Well, not exactly equal to ...

Example: my Doubleverb with OwnHammer IR has Drive at 6.5 and Master at 10. Amp Level is between -20 and -25.
This is comparable (not equal) to Bypass mode, and leaves lots of headroom for boosts, spikes when using the wah, etc.
My studio monitors and other means of amplification have enough power to get things as loud as I need them to be.
 
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