I want to split my stereo input channels so I can Eq one of them. They both would then go to the built-in output. I've installed SoundFloser and AU Lab on Mac OS 10.12 Sierra. I've read through the help pages for AU lab. I couldn't find anything specific to my need. With all the options, it looks like it should be possible. I've tried selecting two mono inputs. I get two left channels as input. I didn't see any way to change the source of the mono input, but I could have missed it.

  • It must be done in SoundDkower and AU Lab? Anything else an option (GarageBand, premiere, audition, Logic)?
    – bret7600
    Commented Feb 1, 2017 at 3:37
  • I'm not picky about the method. AU Lab was the first I found. I just want to adjust one channel's output to my headphone to help with a hearing loss. The only input I really care about is from iTunes.
    – curt
    Commented Feb 1, 2017 at 5:21

3 Answers 3


It could be done using Rogue Amoeba's Audio Hijack which is ostensibly an audio recorder but has really comprehensive routing capabilities too.

You build your path just by drag & drop, it makes the connections for you.

Route a source to two different Channels plugins, kill left in one & kill right in the other - that way each will pass only a single side of the stereo pair.
In front of that you put two EQ plugins, then route both to a single output, headphones/speakers etc.

enter image description here

It's fairly expensive for a one-trick pony, but it's extremely useful if you need the trick it can do.

I posted more examples on https://apple.stackexchange.com/a/203009/85275

BTW, remember to switch it on once you've built it ;-) Button bottom left goes white & the numbers go orange & start to count time.
As a side-effect, launching any specific Hijack preset will launch any apps assigned to it.

  • I'm not going this route, but it is an answer to the question.
    – curt
    Commented Feb 4, 2017 at 2:12
  • 1
    After spending hours trying to find a way to get AU Lab to work, I gave Audio Hijack a try. It was real easy to set up and did what I wanted. I did have to pay $50 for the application. If you have normal hearing Soundflower and AU Lab should be fine.
    – curt
    Commented Feb 5, 2017 at 19:43
  • Glad you got your solution - as I said, one-trick-pony, but it's a very well-crafted one trick.
    – Tetsujin
    Commented Feb 5, 2017 at 19:49
  • And is there something simpler? Basically controlling L-R balance for individual app is enough. By the way, Audio Hijack has small latency, which is noticeable when making something realtime.
    – MrCheatak
    Commented Mar 7, 2018 at 11:23

Indeed you can split stereo input with Soundflower and AU Lab and apply an effect on one channel only.

  1. Set Soundflower as mac audio output,
  2. create a new document in AU Lab,
  3. add another Audio Input… ⇧⌘A,
  4. double click on first (left) input track, change Input Channels to mono and confirm,
  5. adjust accordingly second (right) input track, remember to drag the brown bar to the right cell in the compartment labeled Soundflower Input Stream #1,
  6. turn Panner knobs full left/right on respective input tracks,
  7. apply the desired effect on the track of your choice,
  8. configure Output Settings in Studio ⇧⌘I if necessary.

AU Lab with split channels and Equalizer effect applied to the right channel only:

AU Lab with split channels and Equalizer effect applied to the right channel only

right channel input conifguration


For everyone here not able to make AU Lab run on Catalina:

Just put AU Lab to the Application folder, and manually edit the TCC trust database:

sudo sqlite3 /Users/$USER/Library/Application\ Support/com.apple.TCC/TCC.db "insert into access VALUES('kTCCServiceMicrophone','com.apple.audio.aulab',0,1,1,NULL,NULL,NULL,'UNUSED',NULL,0,1541440109) ;"

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .