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Is there any easy way to listen to the input on a Mac?

For example, assume I have a microphone hooked up to the input (i.e. line in) of my Mac, and I have headphones hooked up to the output of my Mac: is there any way that I can hear what I say in the microphone through the headphones?

This is very easy in Windows XP: simply go to the sound settings for recording devices, check "select" on the line in, and increase the volume – this makes it so you can hear what is said into the microphone.

It has to be in real time; a solution where you record the input and then playback the output later doesn't help.

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    I know this is (years!) old, but you may want to update the accepted answer to the one about QuickTime Player. Line In has substantial buffering/delay issues (when you restart, it's fine, but after a few minutes, it creeps back in) plus it's a third-party app let alone one that's no longer supported by them. Using QuickTime Player however, it's part of the native OS, there seems to be zero delay, and you get a volume control to boot! Anyway, just throwing that out there Hope it helps!
    – Mark A. Donohoe
    Sep 20, 2018 at 0:43
  • The AudioMonitor.app from MTCore Audio was nice but stopped working past High Sierra. The QuickTime method is the best thing in 2023 if you don't want to install new apps.
    – charles ross
    Oct 11, 2023 at 14:47

9 Answers 9

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Take a look at Rogue Amoeba's LineIn. It is a free application which will allow you to do what you want.

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    LineIn can select line-in/mic/digital-in etc, and there are independent volume control.
    – deddebme
    Oct 21, 2009 at 5:39
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    delay introduced is significant. I'd love to see a LineIn-like app working with fast ASIO drivers of the available soundcards.
    – Serg ikS
    Aug 28, 2014 at 7:07
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    Rogue Ameoba released version 2.3 on 2014.09.03 that has completely eliminated delay.
    – xizor
    Sep 24, 2014 at 23:00
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    Currently the free version stops working after 10 mins. I was about to try it anyway but had trouble downloading it. Then I found lifehacker.com/5630844/…, which works.
    – Ryan
    Mar 27, 2017 at 14:16
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    Replaced by rogueamoeba.com/audiohijack
    – grappler
    May 10, 2020 at 20:33
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With 10.6 (and newer, AFAIK) you can launch QuickTime Player.app and choose File -> New Audio Recording. Then just turn up the volume control that is part of the window that appears. You might hear a bit of white noise when there's no sound and the volume is all the way up but the Rogue Amoeba app does the same thing.

Open File menu and select New Audio Recording Increase the volume rocker at the bottom of the windows

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    MAN, I wish I had found this a while ago! This should be the answer, not Line In. This is part of the OS. That's not only third-party, but currently it's legacy, but worse, the biggest issue with 'Line In' is it tends to start to buffer the input, so for instance, using it to route my TV's sound through my computer, it routinely gets out of sync. That doesn't seem to happen with this method. Plus... volume control!! WOOT!
    – Mark A. Donohoe
    Sep 20, 2018 at 0:36
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    There's a ~30 millisecond delay when using this method.
    – Merchako
    Nov 27, 2018 at 20:34
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    I'd go so far as to say its a 500ms delay ... Not really workable. Could this be because it's a bluetooth headset with a mic?
    – Michael
    Apr 2, 2020 at 19:25
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    I have the same delay with the built in mic and wired headset.
    – Hans Kristian
    May 5, 2020 at 7:40
  • I also get a delay of hundreds of ms. The meters on-screen move long before I hear the sound through my wired headphones.
    – Josh
    Aug 17, 2020 at 22:58
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As originally suggested by qu1j0t3, Apple's "AU Lab" provides the ability to listen to the audio input in real-time. (Well, nearly in real-time; for me there is a slight delay from input to output.)

(If those links die, it can also be downloaded from Apple Developer Tools, which may require an Apple Developer account.)

Usage:

In the Document Configuration window, select the existing "Stereo In/Stereo Out" configuration. (If the Document Configuration window is not already open, click File → New to open it.) Then click the Create Document button in the bottom right corner.

In the new "Untitled" window that opens, ensure the icon at the bottom says "Audio Engine Running" (or click to toggle if it says "Audio Engine Stopped"). If necessary, adjust the system's overall input and output volume settings in System Preferences → Sound → Input.

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    Another answer already mentions AU Lab. Your answer is better because it basically follows this outline while the other one does not.
    – Kamil Maciorowski
    Sep 15, 2018 at 6:09
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    @KamilMaciorowski Yes, you are correct - AU Lab was already mentioned in a previous answer, so I have edited mine to mention that. I would have commented/added to the previous answer, but I don't have enough reputation and my suggested edit was rejected, with the reviewer recommending that I add it as a new answer instead. (Sorry, noob problems, not really sure what etiquette I should follow.)
    – Chris Tollefson
    Sep 15, 2018 at 23:36
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    This is a good solution and well explained. The problem is (or at least was for me) that Xcode is currently only available via MacAppStore and one has to use the latest macOS to download it. But luckily Apple still provides AU Lab on this iTunes-Site I found: apple.com/itunes/mastered-for-itunes
    – alex r. g.
    May 9, 2019 at 21:19
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    Signed up to SuperUser to vote you up! ... I needed this for client calls because my headphone are too good at blocking out residual sounds so I was constantly shouting. When I used them in bluetooth mode there was a considerable delay but using them in wired mode this works perfectly.
    – compuphys
    May 5, 2020 at 12:17
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    Both this and the Quicktime answer worked for me, but the Quicktime answer had maybe a 0.5s delay, and this one had no delay, which makes it a lot more natural. My microphone is mono, so I first had to create a new configuration (+ sign at bottom) with mono input and stereo output. Then it worked well.
    – Matthias Fripp
    Sep 8, 2020 at 21:33
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You can also use Garage Band. Choose for example the Acoustic Instrument template (the default audio track in it has no effects) and set monitor to on.

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  • this seems to work just as well as linein, maybe a bit better
    – chrismarx
    Nov 9, 2014 at 0:09
  • Check out the QuickTime Player approach. Even better/simpler and zero lag!
    – Mark A. Donohoe
    Sep 20, 2018 at 0:39
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    Same here. This is the way to go for me with no lag, nor installing additional software.
    – Alex
    Apr 1, 2021 at 12:23
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+50

If you want to use the terminal, you can install sox (i.e. with Homebrew brew install sox) and then run

sox -d -d

Here, -d means "default audio device", and this command specifies it for both the input and the output, i.e. microphone and speakers/headphones.

You can decrease latency by decreasing the buffer size (default 8192), try what works for you:

sox --buffer 1024 -d -d
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  • Very much appreciated, but unfortunately, the delay here (though less than QuickTime) is more than Garage Band. I'd prefer to use terminal, but for my sanity I'm picking the lowest delay.
    – seaders
    Sep 21, 2022 at 12:39
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    sox --buffer 256 -d -d Works for me, thanks! A buffer of 256 samples should result in a delay of 5.8ms. I can play piano on my phone and listen on my MacBook without any noticeable delay. Anything less requires killall -9 sox to terminate the app. CTRL+C does not help when it gets stuck. 😀
    – George Valkov
    Nov 8, 2022 at 3:19
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    sox -V0 --multi-threaded --input-buffer 32 --buffer 128 -d -d This was the lowest I could get. The man page says buffer size is in bytes. -V0 disables printing of errors, and helps keep up the realtime work without getting stuck at startup.
    – George Valkov
    Nov 8, 2022 at 9:34
  • I tried everything apart from GarageBand and forking out for the 60$ Rogue Amoeba app. This was the only thing that worked.
    – oligofren
    Dec 11, 2023 at 14:42
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Another option is "AU Lab" in Developer tools (Developer/Applications/Audio/AU Lab).

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    I couldn't find this in the Xcode developer tools, and had to download it from the Apple Developer website.
    – evolutionxbox
    Jan 29, 2020 at 15:09
  • Could no longer get it to work, even using the mentioned youtube workaround that triggers it from the CLI. No input showing.
    – oligofren
    Dec 11, 2023 at 14:31
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If you're using an older Mac, the application Audio MIDI Setup.app in the Utilties folder (found in the Applications folder) allows* the ability to pass-through input straight to your output.

To do so; click on your input device and then check off the "Thru" checkboxes to pass audio through. However oddly enough I've never seen anyone to get it to correctly work on an Intel based Mac, I've had it work great on some PowerBook G4s however.

The better alternative is to use Rogue Amoeba's LineIn (as said by Richard Hoskins). Personally I use this and find it easier to use.

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    Using Intel based Mac.. can't check the 'thru' checkbox.. looks like it is disabled.
    – Umair
    May 24, 2015 at 18:44
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    This only controls the analog passthrough in a single device/sound card, it will not connect one device to another through software.
    – endolith
    Nov 19, 2015 at 16:24
  • I tried LineIn it's free and does the job. Still a bit of echo but less then with SoundSource.
    – eloone
    Jul 7, 2017 at 21:13
  • Have you tried the QuickTime Player trick above? That seems to do the trick great! Not only is there no delay, but you get volume control to boot!
    – Mark A. Donohoe
    Sep 20, 2018 at 0:41
  • No longer works on newer macs. Using a 2023 M2.
    – oligofren
    Dec 11, 2023 at 14:30
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2020 Update:

Best way: I have an mbox with a condenser mic. When I run the audio thru that, 0 delay and your headphones can be true monitors. I bought a Snowball for ease tho, its a lot to setup.

My solution: Garage band had the best delay for me. Open garage band in the background. Create an audio track and turn on the monitor icon on the track. Shut off any effects.

Easiest solution: Audio Hijack was next best. Its 60 bucks but seemed like cool software if you had more to use it for. Good be noticeable delay. https://www.rogueamoeba.com/audiohijack/.

Free:* Sox but it had a surprisingly long delay for a CLI. See @billfraser's answer

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I tried several things and was getting pretty frustrated until I discovered an old 2010 article by Adam Dachis about using AudioMonitor, part of MTCoreAudio’s developer package for Apple products. (You can download MTCoreAudio for Mac for free at https://mac.softpedia.com/get/Developer-Tools/MTCoreAudio.shtml.) It works perfectly on my Powerbook (OS El Capitan). Once opened up, just click on "Play Through". Now when I travel and my wife or I want to watch Hotel TV while the other doesn’t, to use headphones (you'll need to bring along a fairly long mini plug cable) she or I can just plug my laptop into the TV’s “speaker out” port via the computer’s line in mini plug port (my laptop has two mini ports, unlike the newer models) and the headphones into the computer’s audio out port. The sound is perfectly synched to the TV (no delay) and to avoid any irritating white noise in the background we simply unplug the computer’s power cord and run it on battery mode. Much better than Quicktime (delay) or any other trick I tried.

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  • For those who are having issues with the softpedia website, here is the program's github page. Simply click the "Clone or Download" button and then click the "Download ZIP" button. Extract the ZIP file and you will see the AudioMonitor.app file.
    – flamewave000
    Jan 31, 2019 at 15:54
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    The AudioMonitor.app (downloaded from Github) doesn't appear to be compatible with macOS Catalina. :-(
    – HaggleLad
    Jun 10, 2020 at 20:21
  • This has not worked with new MacOS's since 2018 (macOS Mojave was the last to support 32 bit programs)
    – oligofren
    Dec 11, 2023 at 14:34

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