Unexpected Crackles?

[Klaim]

For some time now I have been noticing sometime when working with my own presets on my Helix (Floor), almost randomly, crackle noises, similar to what would happen if your processing chain couldnt match the given latency goal (like if you didn't set enough buffer in an audio interface, you know what I mean I guess).
It happens randomly and rarely enough in my own presets that I didn't mind, but I have been noticing it for several months to a year now, not sure exactly.

Today while trying random presets (I'm on v3.15, everything reset to factory, then I added my own presets in one of the empty library) and I noticed that I can hear it systematically with the RabeAfro Lead Ambiant preset, but only on the right side, and only when trying to play chords loudly (my guitar is a TAM10 so it's 8 string with lower strings, but the mic is not loud).

I started analyzing whats going on: 

- this is a preset where the left and right side have different chain of blocs and different amps etc, with just a gain pedal and a compression pedal in common at the beginning - even the reverb and delays are different on each side;
- on this specific preset I can only hear the crackles (when trying chords) on the right side; I changed the output node to go to the left side and of course I heard it on the left side, to be sure it was very specific to that chain;
- the preset itself don't have a loud output, actually the output level of both sides are reduced, and the guitar's mics are not super hot either (I usually use compressors to bump the guitar signal a bit actually, but here it's not a preset I made);
- suspecting my new pair of speakers (Headrush 108, getting the jack output from the Helix) I recorded (see below) through Reaper the signal coming from the RCA output which goes into my audio interface (Focusrite Clarett 4Pre Usb), so it is the digital signal but not going through usb but through the S/PDIF channel in. I can hear the exact same crackles and you can hear it in the recording.
- we can hear that the crackles feels coming from before the reverb and delay and I managed to remove the crackles by disabling the amp block on the right side, but it kind of kills the whole thing doesnt it? XD 

So right now I feel like the issue is coming from the preset itself, the block being maybe overloaded in some way, but that feels also wrong from my understanding of how it works, it should not do this kind of thing?

Questions:
1. Am I alone observing this? I wonder if my unit have an hardware issue, so if I'm alone it might mean it is.
2. If not, what would be the cause? Specific to some blocks?
3. Should I consider this a software bug? My (limited but a bit educated) knowledge of the subject suggests that for this crackle to happen the block in question or the chain of block must spend more time than the specified processing deadline, which should not be the case here I think? So...bug?

I didn't find this issue when searching for known issues, the closer I found was issues when using the Helix as audio interface, that I basically never do.

Recording: Rabeafro Ambiant Lead preset, playing chords, with a TAM10 set to position 2 full gain knob, and the recorded through the SPDIF output -> cable -> Focusrite Clarett 4Pre USB -> Reaper (ASIO/Windows10). I hear the same thing (different of course) with speakers (both monitors blugged through the XLR output of the Helix and Headrush 108 speakers plugged to the jack output of the Helix).

https://drive.google.com/file/d/1Nrh5QJ2dkLmr18NYezK5K9H_CLz5DgAz/view?usp=sharing

 

 

 

[DunedinDragon]

Typically crackling like what you're describing is associated with recording and the buffer size being too low or the bit size being too large in your DAW.  The reverb and delay may be a different situation and you may need to increase their headroom parameters on the second page of the parameters.

[PierM]

I'm assuming you are getting the crackling noise within the unit, and not when passing through a DAW. (in that last case, it's indeed buffering which can be easily solved in the DAW audio settings)

 

If you share the preset someone could try to reproduce locally. Of course nobody is getting this problem, so something is happening your side.

 

Anyway, I would try to reset globals and force rebuilding all presets, just in case there is some preset corruption.

[Klaim]

On 3/19/2022 at 8:38 AM, DunedinDragon said:

The reverb and delay may be a different situation and you may need to increase their headroom parameters on the second page of the parameters.

Only the delay on the right channel (the one which is crackling in this preset) have a headroom parametter set to +2.7dB
I pushed it to +6dB and now it doesnt crackle anymore indeed! Thanks!

It is not clear to me how the crackling and the headroom are related technically so if you have an explaination I'm interested (I'm a software engeneer and knows a little bit about audio processing but not enough for understanding that particular case)

Sidenote: Helix did something weird when I first bootup to try this: the signal went through the first processor but not the second, so I wened up with no sound on this particular preset. I think it's again a bug of when you change preset quickly (using the rotation button) and I just rebooted the Helix and it worked. Hopefully it will not happen in live ....

[Klaim]

On 3/19/2022 at 11:14 AM, PierM said:

I'm assuming you are getting the crackling noise within the unit, and not when passing through a DAW. (in that last case, it's indeed buffering which can be easily solved in the DAW audio settings)

 

Yes, I tried to explain this happens without any DAW and the recording is only the SPDIF digital output, there is no audio processing happening here. Without a DAW I can hear the crackling directly on the speaker which is plugged directly on the Helix.

 

On 3/19/2022 at 11:14 AM, PierM said:

If you share the preset someone could try to reproduce locally. Of course nobody is getting this problem, so something is happening your side.

 

 

Maybe I was not clear: this is a FACTORY preset, it's located at position 96 in the FACTORY 1 bank, "RABEA AMBI LEAD" to be very precise.

So can you try it and tell me if you observe the same thing?
The solution given by DuneinDragon works but I don't understand why yet. Or maybe the reverb's "Headroom" should be considered as a buffer size?

 

On 3/19/2022 at 11:14 AM, PierM said:

Anyway, I would try to reset globals and force rebuilding all presets, just in case there is some preset corruption.

 

Though I did reset it completely after upgrading the 3.15 version. I can try again, will report.

 

[PierM]

On 3/19/2022 at 11:31 AM, Klaim said:

Maybe I was not clear: this is a FACTORY preset, it's located at position 96 in the FACTORY 1 bank, "RABEA AMBI LEAD" to be very precise.

So can you try it and tell me if you observe the same thing

 

 

Ok. Thought it was an edited version.

[DunedinDragon]

On 3/19/2022 at 6:25 AM, Klaim said:

It is not clear to me how the crackling and the headroom are related technically so if you have an explaination I'm interested (I'm a software engeneer and knows a little bit about audio processing but not enough for understanding that particular case)
 

 

Line 6 has never been very forthcoming about WHAT they do to fix a problem, so I can only offer my guesses on this.  But that parameter was something that was added to several of the Delay effects a few releases ago in response to user complaints about intermittent clipping on some of the delays.  To my ear it's not digital clipping just standard clipping associated with cropping the tops off of the signal.  Delays and Reverbs are both infamous for being DSP hungry effects so I can only assume it was a matter of allowing you to increase the DSP allocation in certain instances on some of these effects to alleviate that artifact without affecting the latency of the processing.  That way you only have to increase the DSP allocation in those particular circumstances rather than in all circumstances.

[datacommando]

On 3/19/2022 at 10:25 AM, Klaim said:

It is not clear to me how the crackling and the headroom are related technically

Hi,

 

The “Headroom” parameter in the Helix products is added to some, but not all blocks, to suppress exactly the type of cracking that you reported. It’s something to do with the nature of the original item being modelled, for example the Elephant Man. If your signal going into that delay is a little too hot it can create the distortion that you observed. The “headroom” function is available to allow you to adjust it until you no longer experience any unwanted distortion. If you are getting unexpected over saturated, over driven clipping noise, check to see if the block has a “headroom” parameter and adjust it until it you clean it up.

 

It seems that some items are modelled so well, they even include the noisier characteristics.

 

Hope this helps/makes sense.

 

EDIT:

I knew I had see something about this elsewhere - I found this over on TPG. It’s by Ben Adrian -one of the main people behind the Helix models.

 

”If you were using the 70s Chorus or the Bubble Vibrato (or many of the rotating speakers for that matter), they have a control called headroom. We decided to add that parameter because of the following reason:

Fact 1: We model most effects at "guitar level". This is because most effects were designed to be run between a guitar and an amp. Also, many of these effects distort, even when they're not supposed to. So, many analog delays and modulations have some non-linearity at high guitar levels. This is an important part of the effect because even if one does not notice the distortion as "DISTORTION", there is a harmonic complexity added because of the non-linearity. 

Fact 2: Most users set their amp models at higher than unity gain. This is generally fine, but it can cause issues. I think users set up a model and because "loud" sounds "good", the channel volume creeps up higher and higher. I think there's also a psychological thing that, since guitar amps make the guitar louder, a model should boost the signal as well. This behavior will cause amp models to be 6-12dB louder than a bypassed amp. 

Now, if one combines Fact 1 and Fact 2, and one puts a non-linear modulation or delay effect after an amp model, there will be a lot of unreasonable distortion. An effect that is mean to be used guitar level is now being fed a much louder signal and is drastically clipping. It's not digital clipping, mind you, it modeled analog circuit clipping.

So, we came up with "headroom", which is a level-scaling parameter that adjusts the clipping threshold of the modeled analog circuit. If one is putting a non-linear effect after an amp model, one should adjust the headroom control to find a personally satisfying amount of effect clipping. Higher is cleaner.

Sidebar:
My suggested manner for setting amp model volume is as follows.
1. pick your amp model.
2. adjust your tone so that you're happy.
3. bypass the amp. listen to the clean volume.
4. engage the amp and set the channel volume control so that the RMS volume of the amp model and the bypassed amp are about the same.

If users have a loud channel volume AND have the front panel volume control both set at max, digital clipping is quite possible.

Cheers!”

 

That should clear it up.

Edited March 19, 2022 by datacommando
Added quote

[Klaim]

Thanks everybody and in particular @datacommando for the clarifications and historical quote!

I'll add that I remembered today that I have the Big Book Of Helix Tips And Tricks which also have a section explaining the Headroom setting, and with the background given by Ben Adrian it makes a lot of sense.

I'm also noting that I didn't think it would be related to distorsion because the noise felt like lattency issues instead of distorsion to me, so I learned now that actually it can be distorsion. 

Thanks again everyone!