Random noise in Yamaha studio monitors connected to iMac

[snoopdon987]

I am using a 27" iMac model 10,1 with High Sierra in my music studio. I normally use more audio connections than described here but today I disconnected all of them except what I describe here to troubleshoot a noise that I hear in my Yamaha HS50M powered studio monitors. I have a cable with mini TRS plug connected to the headphone jack on the iMac. On the other end of the cable are two 1/4" phone plugs, one plugged into each of the two Yamaha HS50M powered studio monitors. I have a wired Mac keyboard and Dell wired mouse.

It appears I am not able to upload a sound sample here so I have put it on SoundCloud at the link below.

https://soundcloud.com/user-451629486/i ... 3lKoXE2nBV

The four noises at the beginning of the recording happen when I use CTRL > to move from the first to the fourth virtual desktop/workspace then they happen again when I move back. Some of the other noises are when I move the mouse. There is a baseline of noise all the time. The noises starting at 7.6 seconds is coincident with me moving the mouse back and forth.

1. The noise is constant amplitude. The amplitude does not change when I adjust the iMac volume from lowest to highest volume. Playing source material from Chrome (Youtube, TED talks etc.) works normally and I can adjust the volume of that. It is just layered on top of the noise.
2. The noise happens when no other apps are running.
3. If I shut down the iMac the noise stops.
4. If I connect my Sony MDR-7506 headphones to the headphone jack instead of the speakers I do not hear this noise. Source material behaves as in #1 above.
5. If I disconnect the speakers and use the internal iMac speakers I do not hear the noise. Source material behaves as in #1 above.
6. If instead of connecting the other end of the cable to the Yamaha studio monitors I connect it to the AUX in on my NAD integrated amp which is connected to regular stereo speakers and turn the NAD volume all the way up I do not hear the noise (silence). Source material behaves as in #1 above.
7. If I connect the mini TRS plug to my MacBook Pro I do not hear the noise in the Yamaha studio monitors. Source material behaves as in #1 above.

Any help would be appreciated.
Thanks,
Don

[G]

Welcome, Don!

Since the level doesn't change when you adjust the software volume on the iMac, I would guess the problem is somewhere in the hardware between your iMac and the Yamahas. You narrow that down in cases 6 and 7. So it definitely involves the iMac. The noise in your SoundCloud file sounds like moving data being picked up, and that's usually by unbalanced cables acting as an antenna.

Without being able to see your setup, this is just theory, but: If the noise isn't coming from inside your iMac, but only occurs when connected to it, maybe the cause is something right next to the iMac. When your speaker cables are connected to the iMac, are they, as a result, now next to a USB hub, or an external drive, or the iMac's power cable?

Also curious: When testing the MBP, was it plugged in or running off of battery?

[snoopdon987]

"When your speaker cables are connected to the iMac, are they, as a result, now next to a USB hub, or an external drive, or the iMac's power cable?"

No USB hub or external drive. Not running near the iMac power cable. In test #6 I just disconnect the cables from the Yamahas and connect them to the NAD integrated amp.

The MBP was on the charger.

So, I just did some more experiments. I wondered if going THROUGH the NAD would somehow isolate the Yamahas. I connected the iMac headphone out to the NAD as in step # 6 then I connected a stereo RCA cable to the NAD tape out. This output is meant to be able to record another source connected to the NAD with a tape recorder. I connected the other ends, with RCA > 1/4" phone plug adapters, to the Yamaha inputs. Not only do I still hear the noise on the Yamahas but now I also hear it on the speakers connected to the NAD amp!!

I tried using TRS female to male XLR adapters at the Yamaha inputs (they have XLR inputs). I can play source material so apparently the adapters are wired internally such that they pass source material to the right pin on the XLR inputs. Sadly, this does not cure the noise.

Remembering the technique for eliminating 60 cycle AC hum, which is to not use the ground connection, I took a 1/4" phone plug with terminals on the back and plugged it into one of the Yamaha's 1/4" inputs and then just touched the tip of the male RCA plug whose other end is connected to the NAD tape out to the terminal for the tip of the 1/4" plug and I can hear the source material from the Yamaha but the noise is still there.

I am tempted to try something like this:

https://www.markertek.com/product/av-hk ... ransformer

but I don't know if it will work and if not I'm out $90. Unless someone here has a solution I am at the point where it seems time/efficient to switch from the iMac to my MacBook Pro. I have a 27" Apple Cinema Display I am not using so I could connect it to the MBP. It will be a hassle installing Studio One and the other apps I use in the studio on the MBP but I can't have this noise in my recording system. I have a Presonus Audiobox 1818VSL that is the interface I am using with Studio One and I don't think the noise is getting into that but I don't want to take the chance.

Here are pictures.

https://donander.smugmug.com/Public/Studio-Images/

Don

[G]

I still don't think the noise is in your system, per se, merely some flaw from the headphone jack and beyond.

That said, is there any reason you weren't feeding your Yamahas 100% from your Presonus interface? I'd wager that would solve this issue, especially if you used balanced cables from the Presonus to the speakers.

[snoopdon987]

Just FYI, the Presonus Audiobox 1818VSL Main Outs have unbalanced 1/4" jacks. I suppose I could use an adapter to XLR but I don't think this would result in a true balanced connection.

I certainly could drive the Yamahas directly from the Audiobox Main Outs and this would allow me to monitor audio from Presonus Studio One for tracking and mixdown. But I use Chrome, Amazing Slow Downer, Transcribe etc. to watch videos or listen to songs to learn them. For this I need the audio out from the iMac. I don't see any way to get this sound to come out of the Audiobox unless I connect the headphone out of the iMac to the Audiobox and if I do that I'm back with the noise, I think and would also be using up two channels.

I suppose I could use the Yamahas strictly for Studio One and use the speakers connected to the NAD amp for the rest and I would not have the noise with that connection. I added the NAD speakers to the desk because if I am practicing/jamming on guitar to sound from the iMac or a song from Studio One, I need more volume to compete with the guitar amp volume and I didn't want to blow up the Yamahas. I could use Y cables at the Audiobox Main Out jacks to also send that signal to, for example the AUX in on the NAD amp when I need to jam or practice with the Studio One Main Out signal, although this may cause the noise to return but I can try it.

I retired in 2018 from being an IT tech for 20 years and I just have this nagging urge to solve every problem but I guess at some point you have to just stop banging your head against it and do a workaround.

Thanks,
Don

[G]

Oh! From reading the tech specs, the Audiobox 1818VSL seemed to have all balanced analog outs. Even if it doesn't, its outputs are far better than the Mac's headphone jack and the entire box is semi-isolated via digital USB connection. A balanced connection would only ensure that the cables themselves don't pick up their own noise.

With the interface on, and assuming it shows up in Utilities/Audio MIDI Setup, you can't simply select it as an Output in the Sound preference pane? (Some interfaces and apps have been janky with this in the past, so this could indeed not work as expected, but this would be The Way.)

[snoopdon987]

I DO see it in the choices in the macOS audio menu so I'll try it. I thought it didn't work in the past for audio generated within the iMac but I'll try it again. I may still switch to the MBP when I have time because otherwise it just sits on the desk sleeping, especially if it will handle the latest OS. The iMac can only handle up to High Sierra and I fear that soon, the apps I use will kick that OS to the curb.

Don

[snoopdon987]

I submitted this to tech support at the Sweetwater Sound website. I have purchased many music and recording items from them over the last 30 years. My assigned sales rep replied and said he would be happy to discuss this by phone with me but suggested I read this article:

https://support.focusrite.com/hc/en-gb/ ... -monitors-

This sentence jumped out at me: "Whilst a ground loop is not hazardous, it can manifest itself as a constant low-frequency buzz or hum through your audio equipment, or even glitches in audio that are often associated with mouse movement or hard disk activity."

In the past, I have only seen (heard?) ground loops cause 60 Hz hum, not the type of noise I am reporting. But just for fun I inserted a ground lift adapter on the power cord for each of the Yamaha speakers as shown in the 3rd and 4th pictures at the link below, and Voila!, the noise is gone. Go figure.

https://donander.smugmug.com/Public/Studio-Images/

BTW, if I use the "Insert Image" button here and paste the URL in there, will the images show up here? I don't understand how that works and also, is there a way to post a sound file here so I don't have to put it somewhere on the Internet and paste the link?

Don

[G]

Very cool! Glad you got this solved (I thought you had tried ground isolation previously). At least it was truly never "in" your system, so no worries about any recordings you may have done.

The Insert Image button should indeed work as you describe. There's just the risk that the source image will go away at some point, leading to a broken image here. When possible (and condoned/legal), I prefer to upload images as attachments here, then insert them inline.

We had BBCodes for SoundCloud, BandCamp, and many other audio sources in the past. They kept changing their format, however, so it was a real struggle to keep them working. At the moment, the best way to embed audio in a message here is to make a YouTube video of it. I've done this on occasion for Facebook, with their video player, so people can just hit play and not worry about it. Just use a still image if you don't have anything for the video image.