Please help with sound issue in new A/V setup

[beatdat]

We've had a recording issue develop pretty much overnight, and I'm hoping to find a solution to it here.

We've been using a new Soundcraft Sig 22 MTK mixer connected to a new MacBook Pro computer for a few months now. As far as software goes, we've only been using the laptop's built-in software (ie. PhotoBooth). Notwithstanding the growing pains and whatnot of learning how to use the new equipment, we haven't had any major issues in the couple of months we've been using the setup.

But, last Friday we encountered an issue while playing back our recordings: the playback of our recordings now contain a static sound the comes and goes every few seconds - if anything the sound is similar to the "scratching" sound you can hear on some old vinyl recordings; it's intermittent insofar as it dips in and out, and it doesn't seem to last during the entire recording.

To note, the recording is of a church service, which starts with the organ (played on an electric piano), then the pastor's introduction, then a song with one vocal, acoustic guitar and keyboards, and then onto the pastor's sermon, followed by a hymn, and ending with the closing benediction.

If anything, the static sound is most prominent when the keyboard is playing, but sometimes occurs when it's not.

To also note, the static does not seem to be coming from the mixer (to which all instruments and voices are connected), insofar as, when I'm conducting soundcheck or recording the service, I can not hear any static in my headphone monitor which is connected directly to the mixer's headphone monitor output - the static only occurs during playback.

I've tried troubleshooting this to the best I can, but I've hit a wall. I'm pretty sure it's not the USB cable connecting the mixer to the computer for recording and playback purposes, because the static sound only occurs when we playback one of our recordings - it does not occur when playing back any other sounds from the computer (eg. any random youtube song).

It could be the Yamaha keyboard, which is certainly old (likely 25 years old, or so), but I don't know how to check that anymore than I have, which is to make sure the gain/trim and fader are at appropriate levels. The keyboard is also connected to a DI box and changing the attenuation doesn't seem to make any difference.

The only thing I can think of is this: a few days before the static sound started occurring, the person in control of the laptop dowloaded the free Open Broadcaster Software (OBS). He did it so that the image on the laptop screen from the connected webcam could be flipped to it's proper orientation while recording. He has since deleted the software, but the issue persists. I'm wondering if installing the software changed some system settings in the laptop, and that some "artefacts" from the software may have remained even after it was deleted.

If anyone would like to hear what I'm talking about, please watch the first few minutes of this sermon.

Does anybody know what may be causing this and how to fix it? I'm at a loss, so your help is appreciated.

Thanks.

 

[WallyY]

Unplug the power adapter on the Mac. If it goes away, it needs a noise filter before the power adapter.

 

[cbphoto]

That sounds like digital noise, as if a converter is on the fritz.

Sorry I can’t contribute specific info.

 

[beatdat]

Unplug the power adapter on the Mac. If it goes away, it needs a noise filter before the power adapter.

The power adapter is not plugged into the laptop when we record due to the distance between the laptop and the outlet.

That sounds like digital noise, as if a converter is on the fritz.

Could be a possibility. What and where are these "converters"? Are they in the mixer, the laptop, possibly the DI boxes? Maybe this is something I can look into.


Interestingly, both of your responses refer to "noise", which is a good way of describing the issue we're having. Hopefully, this is something to go on, and some more help will be forthcoming.

Thanks for your help, so far.

 

[MrInsanePolack]

Possibly a cord on the fritz? Cords that are going out have a tendency to create a white noise as the plug moves around in the jack. For example, if it was the guitar players cord, everytime he moves his guitar it will make noise regardless of whether or not the guitar is being played. Even if the knobs are in the off position and he is just sitting there, if he moves the guitar it will still create static.

 

[beatdat]

Possibly a cord on the fritz? Cords that are going out have a tendency to create a white noise as the plug moves around in the jack. For example, if it was the guitar players cord, everytime he moves his guitar it will make noise regardless of whether or not the guitar is being played. Even if the knobs are in the off position and he is just sitting there, if he moves the guitar it will still create static.

That very well could be it. While the laptop and mixer are pretty much brand spanking new, the cables are leftover from the old mixer that the church was using; they're probably 20 years old and on their last legs. I'll check the keyboard cables tomorrow, as they're definitely the older ones and the problem seems to occur mostly when the keyboard is playing.

Thanks!