Bass noise from Mod Duo X

S_Righteous · January 13, 2025, 2:20am

I am trying to troubleshoot the noise issues with the Mod Duo X, for the umpteenth time. Trying to get a handle on what is going on, and how to best reduce the noise. I’m looking for any advice which is not already covered by my description of what I am doing. For example, I’m using balanced cables already, but they do not change what I am hearing.

I recently purchased a second unit, to have a backup, since my music is now so dependant on the device, and this has also allowed me to test both units to see if my original one was faulty or anything like that. What I found is that both have the same noise issues, although the pitch of the noise is slightly different in each unit, and this doesn’t change if I swap the power supplies between them.

To start off, I have my unit plugged into a Furman power adapter with surge suppressor, and more importantly RFI/EMI filtration. I don’t have other gear plugged into this same socket, to keep the unit isolated. I use this power bar live because it filters out noise that sometime creeps into cables - but at home, it’s just excess, as I don’t have noise issues with my other gear.

The second point about this noise I wanted to convey, is that there are two components, a brutal high pitch, and a much lower volume bass fluttering.

I purchased a new power supply which matches the Mod stats, but is an ungrounded 2 prong one. In both units this reduced the high pitched noise dramatically. My units would be unusable without this power supply - or possibly only usable at very high gain which would mask the noise, but not remove it. Even with the ungrounded power supply, I do need to gate the input within my pedalboards which are intended for quieter things like vocals, because that noise can be noticeable.

I have my units set to zero input gain, zero output gain, with neither the hardware gate or compressor turned on. The hardware compressor is nice, but the hardware gate always throws pops into my signal. Any gate plug-in in my pedalboard seems to work better than the hardware one, so I skip it.

With the units ungrounded, I still get a bass rumble in my signal, which is coming from the Mod, but not related to the input, or pedalboard even. For example, if I have nothing plugged into the unit, and ensure that no cables are connected to the output within the GUI - there should be zero signal making it to the output, but it doesn’t stop the bass noise. The lights on the output do not turn green, but going into my RME audio interface, the input lights do go on, and I can record this bass rumble to analyze it in my DAW.

If I go into the hardware settings and increase the input gain, (to make my signal much louder than the bass rumble) - a strange thing happens. As I increase the gain (with nothing plugged into the input, and no signal passing through the device) the bass rumble increases in speed as I increase the gain. At +4db, the bass rumble is way more noticeable and fast. If I reduce the gain back to zero, after a few seconds the bass rumble goes back to its slower thumping.

I can have the USB connected to my computer, or not - this doesn’t affect either the high pitched noise when grounded, or the bass rumble when ungrounded. In any case the noise does not sound like a ground hum loop.

Today I was working with a pedalboard, and noticed that if I added a few Audio meter plug-ins, the bass flutter sped up and got worse. Remove them, and it slowed down. So the content of the pedalboard can influence the bass rumble. This happens even if the internal plug-ins are not patched to the output of the device - meaning no signal should be coming out of the physical outputs at all.

My assumption is that the bass noise is related to device noise from the CPU or DA converters, and that adding Audio Meters is affecting that processing. With nothing patched to the outputs of the device, it’s not about internal signal processing, just device noise.

Oh, this issue happens on complex pedalboards that use 60% CPU, and ones that have only one plug-in and use very little CPU. It’s not an overload issue.

Currently I can only think to filter out the bass when recording, and will have to see what gear I need to do that. I may need a mixer to use live which has a bass filter.

I can include a video of me recording this bass flutter.

If the source of the noise is just device noise, what would be the best steps to reduce or eliminate it?
Are there devices which can filter that stuff out?

krullebolle · January 14, 2025, 11:09am

Did you try using an audio power supply that delivers more then 2A?

I think for the mod duo 2 Amps is cutting it close, a decent 3 amp supply “might” correct your issue.

Also, is your net 60Hz or 50Hz and can you audibly tell if the bass noise is in this freq range?

S_Righteous · January 14, 2025, 3:43pm

Thanks for chiming in!
I know this is a tricky topic for most users.

I did a quick phone video of the bass without and with an Audio Meter added to the pedalboard, to see the difference in the bass noise. The noise isn’t consistent, in that the volumes fluctuate quite a bit, and I don’t always hear it, but it can be felt. Here is a screen shot of the frequencies I’m talking about:

I can’t say from this if it’s 50 or 60hz, but I’m in Canada, so our power hum is 60hz.

I will try to source a power supply that gives 3amps. I went with 2 because that is what the DUO X came with.

krullebolle · January 16, 2025, 12:41pm

I assume you are a bass player? I play synths and our PA/mixer blocks all bass sounds( cutoff low frequencies)
Having an mdx myself I can`t say I have the issues you describe… but my gain staging is all high gain. And my hearing is not that good anymore.

I can assume your units are up to date?
What are you listening through? Is your signal going straight to an amp? Or to a mixer? Or to a PC? Not using the headphones?
In the pic you see only 20 Hz bass noise, which I cant hear, only starting at 35 Hz my ear discerns sound. Tested here ( the start and stop pop doesnt count). If you say you feel it, this means you are using a subwoofer/bass amp? My laptop cant generate noises that low and my regular speakers seem to either block anything under 35 Hz or my hearing drops out.

S_Righteous · January 16, 2025, 2:36pm

Just to clarify, that image is showing one of the bass rumbles coming from the Mod Duo X when there is no signal going into it. That bass is being generated by the unit itself.

The sound fluctuates, so sometimes it’s not that low in frequency, and sometimes it pumps up beyond zero db, but not always. It’s a pumping sound really.

I can hear this in my headphones, or through studio monitors. Although it is low in the mix, it is felt, particularly in quiet parts of the music.

I have come to accept that this is just the noise that the device generates, so I am going to rebuild my pedalboards to use much higher gain, and then cut the volume going into my computer when I record. I am also going to filter out those lows when recording.

krullebolle · January 16, 2025, 3:07pm

Sorry that i`m not able to help.
You say you tried isolating circuits? Because I know for sure for example a fridge on the same circuit can cause these kinds of issues ( compressor from fridge running), but I don’t experience it on my unit…

S_Righteous · January 16, 2025, 3:59pm

Yeah, I have my stuff isolated, and use a fancy power adapter that is supposed to filter out noise. I think my issue is making quiet ambient music, and trying to keep the signal path even. So if I have a microphone providing -20db input, the output is also -20db, and I adjust at the mixer if needed. Probably most users are boosting their signals within the unit to such a degree that they wouldn’t ever notice the background rumble.

For me, the premise of matching the output to the input makes microphone feedback less of an issue. The more the device boosts the output, the greater the chance of feedback. At least that’s been my experience.

If you plug your unit to your DAW, and hit record, with nothing plugged into the unit - is there a gain setting where you do start to hear bass rumble? Or is it always quiet? Surely if you boost the output of the unit to +10db, you must hear something right?

plutek · January 16, 2025, 9:07pm

hey @S_Righteous … i’m in toronto, so i guess we’re pretty much neighbours!

this is a thing which i’ve spent some time figuring out in the past. yes, the “low rumble” exists - i’m on a Duo X LE, but i’m sure it’s the same on the production units. with levels optimized, it’s generally not a problem for me. however, there are some times when i’ll throw a hardware noise gate and/or high-pass filter on the output, i.e. when i’m dealing with a lot of soft sounds.

here are some observations which may or may not be helpful - we all have different performance circumstances and requirements!..

the noise you’re referring to isn’t ground loop noise (although there is a small 60Hz component) - even when i’ve addressed all possible ground loops and power supply issues, it’s still there.
this noise (along with other more steady-state mid and high noise) doesn’t change level when the Duo X output or input levels are adjusted (i’m referring to the hardware level controls in Settings). that means we can minimize it’s perceived level by raising the hardware output level as high as possible, for whatever signal we’re dealing with. i.e. it’s a mistake to leave unused headroom, with respect to minimizing these background machine noises that you’re referring to. my Duo X output level is locked at 0, and my inputs work well at -6.5 for the sources i’'m normally using.
playing with the two endless encoders (the big, main knobs) causes a thump for each “click” in the knob position - not a louder thump than the periodic ones already present anyways, but more frequent ones corresponding to knob movement.
if i turn up the gain on whatever is receiving the Duo X output to the point that the low frequency thumping is noticeable, background noise in other frequency ranges (a.k.a. hiss) also is starting to be objectionable. the other noises are steady-state, whereas the low-frequency thumping is periodic, so it’s possibly arguable that those higher noises are less objectionable. ymmv, as they say!
but, still, this points me towards keeping my signal hotter anyways, so all of these noises are out of the way.

i made some video and audio, which may or may not be useful:
WeTransfer link to “rumble” media files

there are:

two audio files - a tone turns on and off 3 times, and then i twiddle the big endless encoder knobs. in one file, the tones are set to peak at around -20 at the Duo X output, whereas in the other the tones peak at 0. if you look at the wave files, you can easily see the difference in background noise which those two signal levels yield. i’d suggest playing the two files at whatever playback level (individually for each) yields an appropriate listening level for the signal (i.e. the tones), and then assessing whether or not the “rumble” (and other noise) level is acceptable or not in each case. …and whether this is at all like what you’re hearing on your Duo X…

[later edit: actually, the “comfortable signal level” playback volume should be the same for both files, since the recording level was adjusted to maximize the peaks of the tones - the background noise levels will be higher in the -20 file, by virtue of the recording level difference]

two video files - these just show a running spectogram of a similar procedure (although they weren’t recorded simultaneously with the audio files, so you can’t line them up). the spectograms are higher-resolution than the picture you posted, so you can see more individual frequency-range peaks, and since it’s video you can see the periodic nature of the lowest thumping noises. also, this gives a good visual sense of noise levels, relative to a signal at -20 or at 0.

i think the files are named intuitively… lemme know if it’s helpful!

bottom line: for me, the noise levels (of various sorts) are acceptably low for normal usage, but i do have to be careful about how i’m running signal levels, and do need to do some dynamics processing in the Duo X such that my dynamic range is not totally huge, which allows me to maximize signal-to-noise ratio.

all best… cheers!
.pltk.

[ note: as a point of forum etiquette, i apologize for the WeTransfer link which will expire in a year. unfortunately, we can’t post audio or video directly, right? ]

S_Righteous · January 16, 2025, 10:11pm

This are interesting observations. Thanks for the time you put into this!
It might take me some time to test and understand it all.

I noticed in your videos, the bass rumble hovers under -70db. That is way lower than what I am experiencing. Mine blows up to zero on a regular basis - but perhaps it’s the gain going into my DAW which needs to be lowered, and the signal coming out of the MOD which needs to be boosted.

I generally don’t like having a device do too much boosting, but I guess if I pull the levels back down on my mixer - I won’t get feedback. I think this is the way I need to go.

krullebolle · January 17, 2025, 9:30am

Aha, seems @plutek has found your problem !

FYI:
In general I keep my signal levels out of the mod at 0dB. That is prolly the reason I have not noticed any rumble. I use the RMPro as limiter in the mod software at -1 dB, and the hardware output at 0dB.
I connect my signal to a line level input on the mixer, in general in PA systems you want your signal to be as hot as possible as soon as possible to avoid picking up interferences. The -20 dB you talk about is in my book very quiet ( I guess I play in a loud band). And a microphone outputs just very low signals anyway, its basically a reverse speaker.

Microphone feedback can be annihilated with a correct placement of loudspeakers, or at home by using headphones? And if those options are not possible, try EQ`ing the feedback out at the mixer ( not in the mod, so you can record the sound from the mod however you want it).
Also, it makes no sense to keep the signal level out of the mod low? Crank it up to 0dB and lower the output from the mixer to the speaker, sound will be as loud as before, but you have less bass rumble frequencies that can give you additional feedback?

If nothing else from the above is possible/working, raise the signal lvl from your mic with a vocal pedal, or a mixer, or a booster, before you feed it to the mod. Some people prefer special preamps for vocals, I guess the mod has allround preamps that have to give headroom to the whole +12dB / -20dB spectrum. This is a huge spectrum and you will defo hear quality differences between the low lvl end (-20 dB ) and the hotter signals, remember its a logarithmic scale ! The mod has digital input processing, so the ADC has it harder on lower signal levels.

Below a screenshot from my tascam recording device manual, you can see they boost every signal in between -68dB and -12 dB with an analog preamp, before they send it to the ADC. Every analog preamp has a potentiometer, allowing fine regulation of the loudness of the signal right before it goes to the ADC. The mod is limited by the ADC in headroom for the lower signal levels.

Also, whilst I think about it, a microphone is a low impedance device ( eg. 16 Ohms) and my line level synths are high impedance (eg. 10 kilo Ohms). This means the electronics from the mod have it easier with my synths then on a microphone, so again, consider a preamp for your microphone
Edit: whilst I think some more about it, the mod is designed for guitar players, and a guitar pickup is also low impedance and low level, so I would assume the mod to be not entirely incapable of handling a microphone.

S_Righteous · January 17, 2025, 8:34pm

This is the most interesting thing - as the ‘device noise’ is not also increased when the signal gain is increased within the signal chain of the pedalboard. So raising the gain, in either the hardware, or the pedalboard is not going to make the noise worse, but obviously a hotter signal can be lowered later and the noise floor is that much further away.

plutek · January 17, 2025, 8:45pm

yes! bingo!

S_Righteous · January 17, 2025, 9:21pm

Just to give feedback on power supplies mentioned earlier in this thread - I did grab and test with a few different ones. I used a 3 amp instead of the 2 amp like the one that comes with the unit. That didn’t make any difference with the bass rumble I had been experiencing.

I’ve been using 2 prong non-grounded ones, and they do not affect the bass rumble, but dramatically decrease the other noise which I get from the Mod supplied power supply. That noise is a whole other topic, but I’m happy to use a 2 prong plug.

plutek · January 17, 2025, 9:22pm

yes, i always also lift ground on the power supply.