MOD Duo background noise level

Ok, did some investigating.
DISCLAIMER: I turned the volume way up and don’t have a comparison for the noise LEVEL but i recorded the noise itself. (it’s mostly F# :slight_smile: )

the black line is output 1 and the red one output 2.
Connecting the MOD to the PC with the usb cable doesn’t make a difference, bluetooth also.
Here’s the audio. (i hope left is one and right is two but it’s possible both are one. doesn’t matter, they’re pretty much the same)
What you hear is the low noise when changing pedalboards, i know this noise from my old laptops headphone jack when the harddrive was working.

AGAIN: This doesn’t reflect the noise LEVEL itself but rather the noise QUALITY
ALSO: No Instrument or Microphone was plugged in.
ALSO2: I only noticed the noise because you told me about it, so i think the level is pretty low.

Is it there if you only plug in headphones, so that there is nothing else connected to power than the mod?

@plutek: In German you say symmetrisch instead of balanced.

Hi Guys,

I’m getting lots of noise but only when USB is attached, tried different leads including ones with chokes but no luck.

It’s pretty unusable with USB attached :frowning:


I assume thats attached to a desktop computer or laptop that is plugged in?

I think we’re all creating ground loops which is causing extra noise. With just a mod plugged in and headphones see what the noise level is, then start plugging in your other equipment. Not sure the best way to address this though other than using a laptop on battery power when you need low noise floor.

Yeah, I guess it’s noise from the computer on the ground of the USB.

I guess the USB and audio components are on the same ground in the Mod Duo?

I have ordered a bluetooth dongle to give that a go, if that’s not fast enough I guess I will snip the ground on a usb cable and see if that helps.

Hi everyone

Sorry for the late reply. Busy times here.

We’re following this issue closely and I’d like to share with you some of our findings and measures being taken.

The issue is related to the audio driver and how it manages the power of the CPU when the audio codec is in use. There is a unwanted current discharge at each buffering cycle that is “contaminating” the input circuits. Because the audio buffering is done at every 128 frames and, as we run at 48kHz sampling rate, the frequency of the current discharges is at 375Hz. Harmonics of this frequency - 187.5Hz, 750Hz, etc - also appear. If you enable “development mode” in the GUI - type “enable_dev_mode()” at Chrome’s Developer Console - and change the buffer to 256 samples you can notice the noise frequency change.

As many interference issues, the overall result is a sum up of multiple factors that range from circuit component deviations to the actual set-up and cables hook up.

The USB connection, although not related the audio, has a strong impact on the noise depending on your computer USB implementation and also on the way that the computer and the Duo are hooked up to the electrical mains. When using some laptops, disconnecting it from the AC power and running on the battery completely changes the noise behavior.

We were working on the improvement of the audio driver in order to improve the power handling but right now, this task is temporarily paused. We are using a forked version of the Linux kernel called sunxi and, because of it’s forked nature, it proved to be unworkable due to the never ending “fix here, break there” cycle.

That said, there is an ongoing effort to move to the mainline Linux kernel (the official version) and, as soon as the migration is done, the audio driver improvement will start moving again.

In the meantime, here are some measures to be taken in order to minimize the issue.

1 - The “contaminated” circuit is in the pre-amplifiers analog section. Changing the Gain stages - Menu/Volumes and Gains - makes a huge difference so the users that require a setting different than Low Gain should try to find the best balance between the Gain Stage, the Fine Gain and also on the internal volumes of the Pedalboards.

2 - Due to the location of the circuits in the PCB, the Input 1 is more vulnerable than Input 2. That said, Input 2 should be preferred for users that require higher gain settings

3 - Try different USB connections and ports between the Duo and the computer

I hope this info helps.

I’d like to remind that we consider audio quality to be one of our top priorities and I’d like to assure all users that we are constantly working towards offering the best sounding device we are able to.

Best regards to all members of the MOD Community


thanks a lot for that, @gianfranco!

it did seem clear to me that this is not a grounding issue, although groundloops can, of course, compound the general noise problem. so, it’s good to hear that you are able to confirm the distinct noise phenomenon related to buffering and periodic current discharge – this is an explanation which corresponds to the worst of what i’ve been hearing.

regarding your comments about input 1 vs 2: is it easy to completely disconnect input 1? i.e. does the physical configuration of input 1 contribute to noise even when nothing is connected to it, and would it help to completely decouple that hardware from the MOD circuit? i usually only use 1 input anyways (which could be just input 2 of course), so wouldn’t mind completely eliminating input 1 most of the time.


One thing Gianfranco, I have quite a bit of audio gear here connected via USB and the Mod Duo is the only thing I am getting noise on.

Is the USB isolated inside the Mod Duo?

This is not necessary

As long as you don’t make any internal connection using Input 1 it will not affect the audio in any way, independently of the noise level it has.

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…this would imply that it might be possible to go a long way towards solving this in software, right? is this being addressed in the “code room”?

the 1.3 testing version seems the same as regards this noise issue.

Hi Gianfranco,

I don’t use input 1 but do have loads of noise when usb is connected. I have to use bluetooth rather than USB to get noise free operation.

we would have to define “long”. it sure is not on the next software release.

because we are talking about the Linux Kernel, the matter gets tricky.

On one side there are people around the world working on it. We could simply “wait”

On the other, we could put resources to accelerate, but that costs money and we need to develop the business a bit more .

Hi @AndyCap

Some computers leak A LOT of noise via USB. I have a desktop that makes even my Mackie Onyx get noisy.

Is your a desktop or a laptop?

Did you try changing the USB port?

In case of laptops, try with or without the AC charger ?

Last, but not least, ever tried a USB hub?

Sorry for the many questions. We surely have filters to isolate the USB, but filters have a limited performance.

If we were to have a device with the USB connection “totally isolated to the point that it would be invulnerable to external noise” the costs would be prohibitive.

And in this case, it is easier to work on the device that is actually sending the noise (the computer/laptop, in your case)

Hi Gianfranco,

It’s a MacPro trash can.

I have lots and lots of musical gear connected via USB and the only one I get noise with is the Mod.

I have tried different leads, direct connection and via hub.

The noise is of a level where connection via USB is not useable.



Just ordered a USB isolator, I’ll let you know how it goes…

@AndyCap I’m interested in how it works for you.

I don’t have any noise issues with the Duo. However I have other gear that has caused havoc on my setup and often wondered about using an isolator. Just never pulled the trigger to get one.

I got the Isolator and plugged it in.

An amazing difference, silence at last.

Here is the before audio:

And the After audio:

This is the isolator I am using:

Worth every penny!


Hello @gianfranco

I hope you are doing well.

Did I miss something or is this issue still there ? I tried a bit of microphone recording over my holidays and the results were not great at all, even when using input 2 (but I have not played much with the different workarounds your are listing here)

What is the difference in terms of hardware between the Gain stage and the Fine Gain ? How would you typically adjust things including the internal volumes of the pedalboard pluggins ?

Thanks in advance,

EDIT: @falkTX would you have any fresh info on the question of switching to the mainline kernel ? Cheers to keep us posted !

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I have recently bought the Mod Duo and I love the idea of it.
Unfortunately I also struggle with background noise… A high frequent buzz.
Does not change with usb plugged or unplugged. It changes frequency when I change buffer size.

Hope this problem will be solved soon.


Hi everyone,

Any progress on this topic ?