Removing pop/crack/glitches from guitar signal

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Bruno Unna
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Removing pop/crack/glitches from guitar signal

Post by Bruno Unna »

Hello!

I'm noticing a few pops, cracks or glitches from my guitar (I'm recording using Ardour/ArchLinux). They are not very bad, but they are noticeable (specially after a screamer plugin has been applied). So I'm hoping to get advice here about plugins that I could use to reduce or get rid of those transients.

I thought this was going to be an easy search for me, as I thought many others would have found this issue before me. Yet, I'm struggling to find a plugin for that specific purpose. Either that, or this is a generic need and I just don't know how to address it using the plugins I already have (basically, the x42, guitarix and calf sets).

Not to be picky, but so far my entire stack is FOSS, and I would like to keep it that way. :wink:

Any pointers will be appreciated. Kind regards.
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Re: Removing pop/crack/glitches from guitar signal

Post by nils »

Setup your system for recording audio and then re-record.
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Re: Removing pop/crack/glitches from guitar signal

Post by Loki Harfagr »

To complete the perfect and acute though a bit terse previous answer you had, since you mentioned using Arch the Good Place starts here:
https://wiki.archlinux.org/title/Professional_audio
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Re: Removing pop/crack/glitches from guitar signal

Post by Bruno Unna »

Thanks, both of ye, for your valuable answers (especially @Loki Harfagr for an actually potentially useful piece of advice).

The fault is mine for not having mentioned that the recommended page is not new to me (as probably you can imagine myself being an ArchLinux user for years), that I've tried for a long time many of the pieces of advice therein contained, with diverse degrees of success, and, perhaps more importantly, that I'm no longer using JACK. I'm currently using pipewire (and yes, I've read the page about pipewire).

I understand ye are trying to help, and I appreciate it. I asked for help. But I was really more interested in ways to digitally process the input, to filter out those transients that (I strongly believe) really come from the source. So that's why I'm asking this question in this forum, as opposed to a more basic, setup-related one.

I've found some plugins that claim to remove noise, but the noise the remove seems to be more of the background type. Certainly, a gateway plugin is not going to cut it for me, because I don't have low-level background noise. It's not regular noise, it's eventual pops that I get (and there are no xruns associated with them). One that I found after having posted the OP is this: https://lsp-plug.in/?page=manuals&secti ... ilter_mono but it feels from the description more specialised in the use cases it serves than what I'm looking for.

To summarise: although I can (and will) review my recording setup, and although I can re-record my guitar tracks, there might be situations when neither of those approaches are feasible. For those, clearly a post-recording processing would be needed. So please don't misunderstand me, don't think that I don't appreciate the provided advice. But the type of solution I'm looking for is a (preferably FOSS, preferably LV2) plugin.

Thanks in advance.
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Re: Removing pop/crack/glitches from guitar signal

Post by bluzee »

For a few pops I would likely just edit manually after the fact. Automated pop removal is probably always going to do things to the signal that you don't like.

Overall I hear what you are saying and you are not going to like what I say now, but your time would be much better spent finding the source of these noise problems and defeating them rather than trying to process them out some how.

It gets very dry here in the winter months and static discharges become problematic. Humidifiers and grounding devices like those used by people servicing or manufacturing electronic devices can help with pops from static discharges.
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Re: Removing pop/crack/glitches from guitar signal

Post by j_e_f_f_g »

How have you determined those pops are not a result of underruns? Many apps either don't bother reporting xruns (and just leave it up to your own ears to detect), or silently adjust for xruns without reporting that adjustment. Does the software you're using explicitly report xruns, and offered no such report during the pops?

In my experience, discontinuuty in audio is nearly always the result of xruns. (Sometimes due to different pieces of hardware not operating well with each other). So, you need to be absolutely sure your elimination of that possible cause is correct before you look for another cause.

For example, have you run the offending plugin in a different host, with only that plugin in operation? If there's really a flaw in the algorithm, you should continue hearing the pops. It wouldn't make sense for the plugin to fail in only one instance/setup. If so, the problem is definitely more than that plugin.

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Re: Removing pop/crack/glitches from guitar signal

Post by Bruno Unna »

bluzee wrote: Thu Jan 27, 2022 8:23 pm For a few pops I would likely just edit manually after the fact. Automated pop removal is probably always going to do things to the signal that you don't like.
Thank you very much for the advice. This suggestion might very well be my last resource, I was just hopeful that some plugin trick would have saved some time from the tedious edition process.
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Re: Removing pop/crack/glitches from guitar signal

Post by Bruno Unna »

j_e_f_f_g wrote: Thu Jan 27, 2022 8:33 pm How have you determined those pops are not a result of underruns? Many apps either don't bother reporting xruns (and just leave it up to your own ears to detect), or silently adjust for xruns without reporting that adjustment. Does the software you're using explicitly report xruns, and offered no such report during the pops?

In my experience, discontinuuty in audio is nearly always the result of xruns. (Sometimes due to different pieces of hardware not operating well with each other). So, you need to be absolutely sure your elimination of that possible cause is correct before you look for another cause.

For example, have you run the offending plugin in a different host, with only that plugin in operation? If there's really a flaw in the algorithm, you should continue hearing the pops. It wouldn't make sense for the plugin to fail in only one instance/setup. If so, the problem is definitely more than that plugin.
Thanks for the time you've taken to reply.

I'm using Ardour, and it's configured to insert marks in the timeline every time an xrun occurs. Even though from time to time (rarely, really) I can see an xrun, for the most time the capture appears to be clean. Yet those noises can be heard.

I'm starting to believe, as per your suggestion, that the issue might be related to the Bird Screamer plugin I have inserted earlier in the chain. Will run some experiments following your advice (probably using Carla), or in a new, clean track. I will also double the sample rate, from 48k to 96k and see if that helps.

Thanks for the suggestions, regards!
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Re: Removing pop/crack/glitches from guitar signal

Post by j_e_f_f_g »

Bruno Unna wrote:the issue might be related to the Bird Screamer plugin I have inserted
If you're inserting screaming birds into your mixes, I should think occasional, minor pops and clicks are the least of your problems.

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Re: Removing pop/crack/glitches from guitar signal

Post by asbak »

If you're getting xruns then the usual suspects are misconfigurations which potentially include

- where both pulse & jack are running and fighting one another for control in an epic battle of evil vs good (although there are methods to run pulse without interfering with jack)
- where an unsuitable kernel is being used
- where power saving features are enabled in BIOS
- where CPU threading is enabled
- where unsuitable or unrealistic periods & frames are set
- where CPU frequency is set to powersave instead of performance mode
- where the jack real time priority is too low
- where the user is not a member of the audio group
- where the user or audio group settings haven't been set in limits.conf
- where background "OS housekeeping" processes are running which strain the CPU and harddrive while what you really want is to have as many computer resources available for use with audio production
- and more potential pitfalls

Unless there's something peculiar about the plugin and it is the plugin that is misbehaving, it's more likely that the plugin is just exposing a more fundamental problem.

You could read Ted Felix's Linux audio guide for many suggestions on a basic setup.
http://www.tedfelix.com/linux/linux-midi.html

If the noises are electrical in nature and not related to xruns then perhaps there are grounding issues or power supply issues or some other kind of hardware problem with the audio interface or the hardware I/O interface on the computer? Without knowing what all of these are it's difficult to make a guess whether these could be causing problems.

PS there are threads in the troubleshooting sections on this website which deal with hunting for the causes of xruns, so be sure to also read those.
One recent example included a user who was tormented by what eventually turned out to be a defective Thunderbolt Intel chipset causing his audio interface to misbehave.
Some Focal / 20.04 audio packages and resources https://midistudio.groups.io/g/linuxaudio
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Re: Removing pop/crack/glitches from guitar signal

Post by Bruno Unna »

j_e_f_f_g wrote: Fri Jan 28, 2022 3:53 am
Bruno Unna wrote:the issue might be related to the Bird Screamer plugin I have inserted
If you're inserting screaming birds into your mixes, I should think occasional, minor pops and clicks are the least of your problems.
Interesting! Would you care to elaborate, please? I'm new to the world of plugins and effects, and I could use some advice on this regard as well. What is the problem with Bird Screamers? Sorry if it's too much a newbie question.
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Re: Removing pop/crack/glitches from guitar signal

Post by asbak »

What it means is that your avant-garde and PETA triggering approach to mixing has outraged Jeff, a bourgeois orthodox beatmaker. :mrgreen:
Some Focal / 20.04 audio packages and resources https://midistudio.groups.io/g/linuxaudio
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Re: Removing pop/crack/glitches from guitar signal

Post by Bruno Unna »

asbak wrote: Fri Jan 28, 2022 6:48 am If you're getting xruns then the usual suspects are misconfigurations which potentially include

- where both pulse & jack are running and fighting one another for control in an epic battle of evil vs good (although there are methods to run pulse without interfering with jack)
- where an unsuitable kernel is being used
- where power saving features are enabled in BIOS
- where CPU threading is enabled
- where unsuitable or unrealistic periods & frames are set
- where CPU frequency is set to powersave instead of performance mode
- where the jack real time priority is too low
- where the user is not a member of the audio group
- where the user or audio group settings haven't been set in limits.conf
- where background "OS housekeeping" processes are running which strain the CPU and harddrive while what you really want is to have as many computer resources available for use with audio production
- and more potential pitfalls

Unless there's something peculiar about the plugin and it is the plugin that is misbehaving, it's more likely that the plugin is just exposing a more fundamental problem.

You could read Ted Felix's Linux audio guide for many suggestions on a basic setup.
http://www.tedfelix.com/linux/linux-midi.html

If the noises are electrical in nature and not related to xruns then perhaps there are grounding issues or power supply issues or some other kind of hardware problem with the audio interface or the hardware I/O interface on the computer? Without knowing what all of these are it's difficult to make a guess whether these could be causing problems.

PS there are threads in the troubleshooting sections on this website which deal with hunting for the causes of xruns, so be sure to also read those.
One recent example included a user who was tormented by what eventually turned out to be a defective Thunderbolt Intel chipset causing his audio interface to misbehave.
Thank you for all the useful information! However, I don't think the problem is linked to xruns. I'm not getting xruns when recording. Also, I'm not using JACK, but pipewire, which in my experience so far doesn't seem to be introducing any latency with respect to what JACK would handle. On the contrary, it's very responsive. So that rules out points 1, 6 and 9 from your list, and significantly reduces the probability of points 2, 4, 5 and 10 (because I fail to see audio issues in other use cases, same computer and configuration).

My DI is an evo4 (by Audient), and it's explicitly configured in pipewire to use 48 KHz sample rate, with 128 samples per frame. So not a lot of CPU pressure on that side.

My BIOS is not configured in power saving mode. I'm not running a vanilla kernel, but zen linux. So from your list, the most suspicious element would be the frequency scaling policy. I've checked, and yes: I was running with the 'ondemand' policy. I've temporarily set it to 'performance', and I *think* I perceive an improvement, a slight reduction of the noise. So thanks a lot for the suggestion.
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Re: Removing pop/crack/glitches from guitar signal

Post by Bruno Unna »

asbak wrote: Fri Jan 28, 2022 8:55 pm What it means is that your avant-garde and PETA triggering approach to mixing has outraged Jeff, a bourgeois orthodox beatmaker. :mrgreen:
Oh, I'm sorry, Jeff! :D As I said, I'm just a newbie, but more than willing to learn the proper ways of mixing, from more seasoned people.
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Re: Removing pop/crack/glitches from guitar signal

Post by j_e_f_f_g »

Bruno Unna wrote:What is the problem with Bird Screamers?
They sound like high-pitched banjos.

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