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Old 12-27-2019, 02:06 PM   #1
ajmich
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Default High-pitched noise in audio on iMac Pro 2017

Experiencing an annoying high-pitched noise in the audio of an iMac Pro (2017) using Reaper current version -- NOT physical noise such as a fan, etc. The noise winds up on any recordings made.

OS and all software up to date. Have removed all external gear, drives, etc., in attempting to pinpoint the source, leaving only the internal SSD drive running. The noise volume is low but constant, unaffected by any level settings.

Along with the tone is random sharp clicking, sounding much like a typewriter. WTF!?

Anyone have any ideas as to source and how to get rid of it?

The attached zip contains a 10-second sample of the noise. TURN YOUR AUDIO DOWN before playing as the file is recorded at high volume. The actual noise is probably 40dB down or more, very low but quite obvious during soft music or between tracks.
Attached Files
File Type: zip mac-noise-10sec.mp3.zip (102.0 KB, 277 views)
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Last edited by ajmich; 12-27-2019 at 07:30 PM. Reason: Attached file containing audio sample
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Old 12-29-2019, 11:23 AM   #2
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Are you using a usb audio interface?
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Old 12-29-2019, 11:27 AM   #3
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Quote:
Originally Posted by Ideosound View Post
Are you using a usb audio interface?
Yes, but tested with no USB connections, noise still present.

My interface is the Audioquest Dragonfly Cobalt.
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Old 01-02-2020, 11:10 PM   #4
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It seems, this discussion should continue here?

https://forum.cockos.com/showthread.php?t=223551

Did you try a different audio interface in the meantime? I have absolutely no issues with my iMac Pro and a Thunderbolt Quantum 2 by Presonus.
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Old 01-03-2020, 06:55 AM   #5
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Weird Clicking comes in different flavors, usually makes one think of mechanical drive failing or clocking mismatch, but that typewriter thing? Hmmmm? And after careful repeated listening and consulting with experts...that definitely is a squeal

I would say boot as another user to see if the OS X sound prefs got hosed. Barring that, go into the user library (make it visible by holding option while going to Go menu) and remove any Apple sound or audio preferences, and move the whole plugins folder to the desktop so it boots without any plugins.

Maybe something in the Reaper routing is causing it to feedback? If you don't have a alternate user to boot as, create one in the Users And Groups System Prefs from the left menu, and allow it to be an admin. This will create a new Reaper setup from default as well as for Apple, and also of the interface software, if it has any.
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Old 01-04-2020, 10:08 AM   #6
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Quote:
Originally Posted by ajmich View Post
Yes, but tested with no USB connections, noise still present.

My interface is the Audioquest Dragonfly Cobalt.
I'd heard the security T2 chip was causing some issues with USB interfaces, that was why I asked...
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Old 01-04-2020, 10:35 PM   #7
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Quote:
Originally Posted by vdubreeze View Post
...And after careful repeated listening and consulting with experts...that definitely is a squeal I would say boot as another user....
Thanks, enjoyed your response; I do need to laugh about this damned thing, it is such a headache! Audioquest (actually, their designer of the Dragonfly DAC) says,

"The clicking is the asynchronous feedback not working. The 2, 3, 4Khz tone I have no idea. We don't have anyone else experiencing that. If you can dig up a copy of HALLab from Apple you can look around there and see if something is doing anything to cause these problems. Or open the Terminal in the Utilities folder and run top and see if there are any processes that seem out of the ordinary."

Hmmm, well.......... I chased 'HALLab' down a dark alley to nowhere, and 'top' revealed a huge number of processes that I cannot really interpret at my pay grade, but none of those running seemed suspect.

The alternate user idea looked promising, but ultimately resulted in the same issue -- thanks for trying. Removing those preferences made no difference. And I could not find a plugins folder that contained anything significant [most were empty], although I do have Izotope Ozone plugins in there somewhere.

At this juncture I'm faced with a clean install of Catalina, holding off on the plugins just in case, and testing the system again while fresh. Humph. BUT, pretty much resigned to using the iMac Pro's headphone jack to feed the recorder and skipping the DAC entirely -- as it has been pointed out to me elsewhere (and, pointed-ly), that the audio from the Mac is greatly superior to the vintage circuits in the analog recorder (Otari) that I'm using, so in essence there is no advantage to the DAC anyway, at least with the iMac. Wish I was comfortable with that. Some listening tests would probably be convincing. I have other machines that would benefit from the Dragonfly though, so not a complete waste of money.
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Old 01-05-2020, 04:08 AM   #8
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How should a clean install of Catalina help, if you reported in the parallel thread in the general forum, that the Dragonfly has similar issues, when you tested it on a PC?

Why don‘t you use your Steinberg interface to feed the recorder ... it has Line Out, hasn‘t it? And that is a much better choice, than headphone output to feed a recorder.

PS: And why do you use an analog tape recorder at all, when you can record digitally on the iMac Pro and if needed simulate „tape audio“ with plugins?
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Old 01-05-2020, 09:39 PM   #9
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Quote:
Originally Posted by Aymara View Post
How should a clean install of Catalina help
I suppose that a clean install is just a mostly useless, compulsive way to convince myself that there are no additional oddities, remnants, whatever, lingering in the file system. I do clean installs about twice a year anyway. To each his own, yes?

The Steinberg is a fine unit leftover from another setup; I just need to acquire the necessary cables.

Actually you are quite mistaken about the headphone output of the iMac -- it is in fact a multi-purpose audio output and (I am told) is of very high quality. So good, I doubt I even need the DAC at all.

The analog tape is for specific projects having nothing to do with producing a certain tape sound. The choice of recording method has nothing to do with the issue. I simply require analog tape for output of said projects. Not everyone desires everything to be done digitally. Presume much?
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Old 01-05-2020, 11:59 PM   #10
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Quote:
Originally Posted by ajmich View Post
The Steinberg is a fine unit leftover from another setup; I just need to acquire the necessary cables.
And that seems to be the fastest and cheapest solution to your problem, because you can use line out.

The headphone jack of the iMac is high quality, yes, but according to Apples’s specs it has the wrong impedance (24 Ohm) to feed the line in of the tape machine, so it‘s a compromise and not an ideal solution.
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Old 01-06-2020, 07:14 AM   #11
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Quote:
Originally Posted by Aymara View Post
The headphone jack of the iMac ... has the wrong impedance (24 Ohm) to feed the line in
"Wrong" impedance? I've not had any problem in that regard. It drives the line in just fine!
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Old 03-06-2020, 08:35 PM   #12
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Exactly what is connected and how?

Are you still running audio out of your mac, through the old tape player, and back into the mac, using unbalanced I/O to connect to a tape machine that has balanced I/O?

Who gives a damn about DAC quality if you've already failed at the most important bit for audio fidelity, making sure you have the correct analog interconnect configuration.

Unbalanced (consumer) to balanced (professional) and then back again, without isolation transformers? FAIL. Go directly to jail. Do not pass go. Do not collect $200.

Some gear, like the on board sound in your mac might do better than other gear, like your usb device, but just because you can get away with it with certain combinations of gear doesn't make it the right way to do it.


https://www.avw.com.au/images/techpa...e_note_110.pdf

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A second reason for balanced interconnect’s bad reputation comes from those who think connecting unbalanced equipment into “superior” balanced equip-ment should improve things. Sorry. Balanced inter-connect is not compatible with unbalanced. The small physical nature and short cable runs of completely unbalanced systems (home audio) also contain these ground loop noise currents. However, the currents in unbalanced systems never get large enough to affect the audio to the point where it is a nuisance. Mixing balanced and unbalanced equipment, however, is an entirely different story, since balanced and unbalanced interconnect are truly not compatible. The rest of this note shows several recommended implementations for all of these interconnection schemes.

https://www.ranecommercial.com/legacy/note151.html

Quote:
One may ask, if the balanced solution is best, why isn't all equipment designed this way? Well, reality takes hold; unbalanced happens.

Back in the early days of telephone and AC power distribution a specific class of engineers evolved. They learned that telephone and AC power lines, due to their inherently long runs, must be balanced to achieve acceptable performance. (To this day, many telephone systems are still balanced and unshielded.) In the 1950s, hi-fi engineers developed systems that did not necessitate long runs, and used unbalanced interconnection. The less expensive nature of unbalanced interconnection also contributed to its use in hi-fi. These two classes of engineers evolved with different mind-sets, one exclusively balanced, the other exclusively unbalanced. The differing design experience of these engineers helped form the familiar balanced and unbalanced audio worlds of today.

Now add spice to the pot with the continued price decrease and praise devoted to balanced, "professional" audio interconnections with the desire for better audio performance at home, and one sees the current trend of merging balanced and unbalanced systems arise. Home studio owners, previously on the unbalanced side of the fence, dream to jump but unfortunately straddle the fence, getting snagged on the fence's ground barbs when connecting their new balanced equipment.
Except in your case it's your new gear that is unbalanced, and your old gear that is balanced.

As far as I can tell, the fundamental problem is a ground loop, and you're trying to solve it, not by using balanced I/O, but by playing around with different bits of gear that have unbalanced I/O, hoping to find one that has paper specs that make you feel good, and also, for whatever reason, aren't as effected by the ground loop as the other ones were.

This is nuts. I'm not trying to have a go at you, but I think you have become so fixated on paper DAC specs that your whole perspective on audio fidelity is backasswards. I mean, you're worried about the quality difference between two modern 24 bit 96k converters, while running them through an old tape machine, using incompatible analog I/O configurations!

The fact that the ground loop noise when using the USB DAC makes it sound worse than the on board sound on your mac should tell you about the relative importance of DAC specs vs analog interconnect configuration. Even with the on board sound, though it may be low enough in level for you to not notice it, there is still a ground loop, and it will add extra noise.

Fix what is broken. Unbalanced to balanced is broken. It doesn't matter how good the DAC measures on paper. You're very unlikely to get that level of fidelity from it with incompatible analog I/O circuits, as demonstrated by your present predicament.

Last edited by drumphil; 03-07-2020 at 12:18 AM.
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Old 03-07-2020, 01:11 AM   #13
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I'm going to run you through exactly what I would do if I had your setup with those issues to figure things out.

Firstly, lets start with the absolute basics.

Plug the cobalt in to the computer, with no other external devices connected at all. Not USB, not audio cables, not anything. Connect some headphones to the cobalt, and listen to something from your mp3 collection, or from youtube or whatever.

Is the squeal there? Are the clicks there?

If yes, then the problem is either the cobalt, the mac, or something to do with how they work together. If just the clicks are present, but no squeal, then maybe it's the T2 issue. I'd be very surprised if the squeal was there, because it sounds very much like ground loop noise to me, and a ground loop isn't possible with passive headphones. Regardless, at that point nothing you do with the rest of the setup will solve the issue, because what's coming out of the cobalt is already bad.

If no, then we've established that the cobalt can output clean audio when hooked up to a passive device where there is no possible ground loop. So, that's a good start. That means that it isn't the T2 chip problem, or anything to do with software or operating system configuration.

Which leaves the interaction between the devices through the analog connection between them as the issue.

But the other audioquest USB device didn't have the problem, and neither does the on board sound! Yeah, well, that's great, but for whatever reason to do with it's design, the cobalt exacerbates the ground loop noise more than the other devices do. It's still a ground loop problem. If it wasn't, then you couldn't get clean output using headphones.

Last edited by drumphil; 03-07-2020 at 02:07 AM.
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Old 03-07-2020, 02:19 PM   #14
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What drumphil said.

Its the Dragonfly IMO. Which COLOR of dragonfly do yo have as that sample rate must match the sample rate in the AMS setup in OSX on the Mac
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