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An Experiment for Mac Users


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Can anyone try the following experiment:


-) Listen to a track played via iTunes.

-) open a terminal window

-) start "top"

-) find the pid of coreaudio and itunes


-) quit "top"

-) renice them via


sudo renice -20 -p PID_ITUNES

sudo renice -20 -p PID_COREAUDIO


-) listen again

-) report differences


I am curious about your observations.


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Thanks for the very clear instructions.


I've played with this a bit some time ago. However I did not, at that time, think to renice coreaudio. Also I've improved some other elements in my setup since that time.


Will try to give this another go during the weekend.


2013 MacBook Pro Retina -> {Pure Music | Audirvana} -> {Dragonfly Red v.1} -> AKG K-702 or Sennheiser HD650 headphones.

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An easier way to discover the PID (Process ID) of iTunes and CoreAudio is to launch Activity Monitor and type Core or iTunes in the oval-shaped filter field in the upper right corner.


Incidentally, I tried writing an AppleScript to renice the Spotlight processes, but mdworker regularly quits and relaunches with a different PID each time. It's easier to simply disable Spotlight!


HQPlayer (on 3.8 GHz 8-core i7 iMac 2020) > NAA (on 2012 Mac Mini i7) > RME ADI-2 v2 > Benchmark AHB-2 > Thiel 3.7

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I am curious about what you hear.


I am running a previous generation 24" iMac into an Audio Note DAC Kit 2.1B Signature using the HagUSB input with a Tentlabs Clock via a Locus Design Polestar.

Amplifier is an Audio Note Kit One, speakers Audio Note AN-K/SPa. All other wiring Audio Note.


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The Spotlight Privacy setting allows you to exclude folders or entire disk volumes from Spotlight. If you add all your hard drives to the Spotlight Privacy list, you will effectively have turned off Spotlight.


System Preferences > Spotlight > Privacy.

Click the + button.

Select your hard drive.

(Alternatively, you can drag hard drive icons to the list window.)


Repeat the last 2 steps for each disk volume (i.e., hard drive partition).


HQPlayer (on 3.8 GHz 8-core i7 iMac 2020) > NAA (on 2012 Mac Mini i7) > RME ADI-2 v2 > Benchmark AHB-2 > Thiel 3.7

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Claude, I belive the renice (linux version of unix nice) command changes the priority of a process in the kernel's scheduler.






A: Mac Mini => Peachtree Nova => LFD Integrated Zero Mk.III => Harbeth Compact 7ES-3 | Musical Fidelity X-CAN V-8 => AKG K 701

B: Airport Express = > Benchmark DAC1 => Rega Brio-R => B&W DM 601 S2

C: Airport Express => AudioEngine A2

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You can create an AppleScript and save it as an Application.


Paste into AppleScript Editor:

do shell script "renice -20 -u _coreaudiod" with administrator privileges


HQPlayer (on 3.8 GHz 8-core i7 iMac 2020) > NAA (on 2012 Mac Mini i7) > RME ADI-2 v2 > Benchmark AHB-2 > Thiel 3.7

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Use Speed Freak which accelerates the top most app. in this case iTunes ..activate and hold..it should say "accelerating iTunes" ..dunno if it makes much of a difference in SQ? ..but there's always the comforter effect ..aka placebo ;)


It's free btw;




iMac i5 w/ ROON > HP Stream w/ Fidelizer > Intona Industrial > Singxer F-1 DDC > ABBAS DAC3.1SE > Line Magnetic LM-518IA > Altec 604-8G in Custom 350L Cabinets + REL R-528

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"but there's always the comforter effect ..aka placebo ;)"


This 'effect' - as you call it - may be responsible for more money being spent unnecessarily (i.e. buyer can't hear the presumed improvements, but is intentionally buying because he/she believes they are buying something that is 'better') on audio gear than all the disingenuous audio marketing ever devised.


I have seen this even in non-audiophiles purchasing audio gear. More specifically, I've instructed people to go to audio store to audition a particular item (always the best known value for a particular brand's lineup) for presumed purchase - "if you like it, you should buy it, and dont let the dealer talk you into anything else."


In variably what happens - unless I am with them - is that they will come home with the next model 'up', which is not always even an improvement irrespective of the increased costs. They didn't let the dealer talk them into something else, they did it themselves!


Quite frustrating, 'cause when you ask what they liked better, the answer is usually a sheepish "well, I assumed it would be better, and I decided I could afford more than the budget I gave you when I asked for recommendations" One example that I can recall was the Adcom GFA-535 amp - someone with no need for additional power upgraded to an amp that I don't think sounded as good - the next model up.




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I don't speak Winders very well, so I don't know.


"An Audio Device should, but is not required to, support an arbitrary number of clients. An error will be returned if a given device refuses to accept another client, or the device is in "hog" mode. In hog mode, a device will only allow one client at a time. This is intended to provide a client a way of ensuring that it is getting all of a device's time. Hog mode is a 'first come, first served' service."


From: http://darcs.brianweb.net/vendor/powerpc-apple-darwin/include/CoreAudio/AudioHardware.h


There's more information on this and implications of its use if you poke around. For example, the latest version of JACK just added this feature. As far as I know (in other words, don't even bet a nickel on this) none of the audio playback applications use hog mode. Yet.


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has anyone come to firm conclusions with this yet?

Will it work with Amarra?


\"It would be a mistake to demonize any particular philosophy. To do so forces people into entrenched positions and encourages the adoption of unhelpful defensive reactions, thus missing the opportunity for constructive dialog\"[br] - Martin Colloms - stereophile.com

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There's at least three programs that will perform this command line operation automatically. I'm not sure if all will work right in Snow Leopard, however. Each will give whatever application you choose priority in resources.


Beats me if it works with Amarra, though.


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  • 2 weeks later...


I had to join this forum after reading this and trying it out for myself.

I am running a Macbook Pro with Snow Leopard through a very heavily modified Beresford TC-7510 via optical connection, into Musical Fidelity A3.2 Pre-power combo and Shahinian Arc speakers.


I've run a test with a few of my choice test tracks. The only problem I've had is that COREAUDIO does not show up in my activity monitor, so I've only renice'd the PID for iTunes, but I can certainly tell a difference for the better.


Less fatiguing, it's taken an edge off the sound, most noticeable in the fact that strong 'S' vocals are less sibilant. There also seems to be more fine detail coming through and I've noticed decay in instruments that I've never noticed before. It's as if you can suddenly look deeper into the recording. I'm mightily impressed.



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Hi lovejoy,


Thanks for your comment, I am hearing the same things you are hearing. The thing that was bugging me was that I was getting varying degree of performance from itunes, sometimes it would improve on a restart. If I give the process high priority the results are better and more consistent.


As for the PID of coreaudio you can try opening a terminal window and doing a "ps -Al"


This should give you a list of all running processes with their PID and also their nice value.


Hope that helps




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Yes, inconsistent results. Tell me about it ;-). I've been getting that from iTunes for a long time and had no idea what it was. I put it down to my home baked power supply which I've been tweaking around with, but never really sorted the problem out. It never really occurred to me that it could have been down to the priority iTunes was being given. I'll run it more over the course of the weekend and report back on its consitency.


Thanks for the tip on finding the PID of coreaudio, I'll give that a go too.



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