Motu M6 Crackling Noise on all 4-in Channels and Input/Playback Gain Knobs.

[MWKMWK]

Hi All,

I'm new here and just bought a Motu M6 which is exhibiting this behaviour. While any audio is being fed into the inputs, if you rotate the gain knobs on that channel, it introduces this crackling noise in the signal path (it is picked up in the recording if you are recording that channel). The same behaviour happens with the Input/Playback knob if you are monitoring live audio and the audio being played back on your computer—rotating that knob creates crackling.

This is not normal and I'm wondering if others have experienced this issue as well. Here's a link of the audio issue (I tried uploading a Mp3 on the forum but it didn't work)

Audio file.
http://sndup.net/vxf3

I have returned the unit, and I am waiting for a replacement. But, I figured I would post about it in case anyone else is experiencing this. Maybe there's a quick fix that could help someone else out in the future.

I tried firmware update, multiple cables and instruments, and even different computers, it's definitely the unit itself.

[stubbsonic]

Yea, I have a vague memory that this is the case for my M4, as well. I'm not sure, but it MIGHT be possible that the knobs provide stepped changes in value as opposed to a smooth analog behavior. I hope I'm wrong about this.

Can't test this right now, but let me know if you would like that.

[MWKMWK]

It definitely does sound stepped as you say. But how would that ever been green lit as normal behavior for a gain knob? It introduces artifacts in the signal path. So anytime you adjust the volume of any channel while you're recording, the 'stepping' is captured as digital noise.

Since when would any knob noise be considered normal with high end audio equipment?

I would think that your unit is also faulty if you have the same behavior. I'm hoping that's the case because I was looking forward to having a unit that didn't have this issue.

[stubbsonic]

The idea would be that you set the level before you track. And that adjustments to the monitor volume knob causing zippering wouldn't matter.

I can't get into the minds of the designers. If those are potentiometers, and the conversion for their gain values is fixed at some insufficient resolution (like 8 or 10 bit?) then zippering will be noticeable. If the resolution is higher like 16 bit or more, then perhaps the zippering would less noticeable. Or perhaps a smoothing algorithm is what is lacking-- something that says ok, the value jumps from here to here, let's interpolate.

I don't have any answers for any of that. I don't use my M4 for mission critical work, so I'm not feeling betrayed. But I can get why that would be a problem for some users.

[MWKMWK]

Received a replacement unit and it has the same issue. Either it's part of a bad batch or this is how MOTU designed the unit. I really don't understand how this would pass QC. You shouldn't have any obvious interference/noise going into the signal path from a simple adjustment of volume/gain. On this unit the headphone controls also exhibit some noise when you rotate the knobs.

I've contacted MOTU Support to see what they think. I really hope this can be resolved because the MOTU M6 is exactly what I need for my setup (minus the noise from changing the gain on different channels). I'll be using it live sometimes so this is why this issue will not work for me.

Again, I don't understand how so much noise added from using the unit is considered 'normal', especially from a higher end piece of kit as the M6. My Steinberg UR22 knobs are dead quiet, that's sad...

Anyone else can check their units to see if they have this behaviour?