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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.

enharmonic
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Senseful
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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 '18 at 00:43

9 Answers9

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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

maelvls
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Brian Ashe
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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 '18 at 00:36
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    There's a ~30 millisecond delay when using this method. – Merchako Nov 27 '18 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 02 '20 at 19:25
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    I have the same delay with the built in mic and wired headset. – Hans Kristian May 05 '20 at 07:40
  • 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 '20 at 22:58
  • make sure to go to Sound preferences and select your input source _before_ you create a new audio recording. – Peter Perháč Nov 24 '21 at 11:03
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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.

Richard Hoskins
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    LineIn can select line-in/mic/digital-in etc, and there are independent volume control. – deddebme Oct 21 '09 at 05:39
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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 '14 at 07:07
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    Rogue Ameoba released version 2.3 on 2014.09.03 that has completely eliminated delay. – xizor Sep 24 '14 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 http://lifehacker.com/5630844/audio-monitor-simplifies-monitoring-an-audio-input-source-on-your-mac, which works. – Ryan Mar 27 '17 at 14:16
  • In SoundSource look for "Open Play-Thru Window" and then "Start Play-Thru". I tried, it technically does what I want but the sound is very bad, there is a lot of echo despite tweaking to the settings.. I don't know if it's my mic or my headphones that are bad or sth else. – eloone Jul 07 '17 at 21:03
  • The free version of SoundSource stops working after 10 minutes, but on their legacy page they still have a download option for LineIn which still works on High Sierra currently. – rich Jan 14 '18 at 19:07
  • Well, as of 9/19/2018, Line In still has the delay. It's not at first. It seems to be buffering or something. Restarting it fixes the issue, temporarily. However, as @BrianAshe said in his answer below, use the QuickTime Player! It's built-in, there's never any delay, and best part, you get a volume control for it too! – Mark A. Donohoe Sep 20 '18 at 00:38
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    Replaced by https://rogueamoeba.com/audiohijack/ – grappler May 10 '20 at 20:33
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    This answer used to be great and I used LineIn. Now the better answer is the one below, using QuickTime Player. That is built-in to the OS simpler to use (I downloaded Rogue Amoeba's software, but didn't quickly figure out how to make it work) and free. – David Silva Smith May 27 '20 at 14:55
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    LineIn no longer functions on newer OS versions, and SoundSource no longer supports playthrough. The only option from Rogue Amoeba is now the $60 AudioHijack. – Josh Aug 17 '20 at 22:57
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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.

Chris Tollefson
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    Another answer already mentions AU Lab. Your answer is better because it basically follows [this outline](https://meta.superuser.com/a/5330/432690) while the other one does not. – Kamil Maciorowski Sep 15 '18 at 06:09
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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 '18 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: https://www.apple.com/itunes/mastered-for-itunes/ – alex r. g. May 09 '19 at 21:19
  • Thanks @alexr.g. - that link is much easier to get to, so I've updated my answer with it. – Chris Tollefson May 10 '19 at 07:17
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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 05 '20 at 12:17
  • Thanks @compuphys for the +1! Bluetooth introduces additional delay for me too, and I think that's a [common experience](https://superuser.com/a/1284818). For anyone who's curious, [Bluegiga](https://en.wikipedia.org/wiki/Bluegiga) (now SI Labs) has published some [Bluetooth audio latency figures](https://www.silabs.com/community/wireless/bluetooth/knowledge-base.entry.html/2015/08/06/audio_latency_withb-7BGG), ranging from 30 to 150 ms depending on the [Bluetooth profile](https://en.wikipedia.org/wiki/List_of_Bluetooth_profiles) and codec your devices are using. – Chris Tollefson Jun 30 '20 at 00:00
  • This is the only solution here that worked for me, thank you! – Josh Aug 17 '20 at 23:02
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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 08 '20 at 21:33
  • This works well on Catalina with a 2019 MBP. I kept getting errors from AU Lab about my input device not having the correct number of channels, you have to create a new User Configuration with the + at the bottom on the new document screen, then you can create a mono input -> stereo output config. – Andy Fraley Dec 09 '20 at 19:26
  • Zero perceptible latency using the AU Lab method on M1 Mac Mini with latest Big Sur — if, and only if, I select the "External Headphones" output in AU Lab, which routes the input to the analog 3.5mm headphone jack. (I had bad latency with other outputs.) – Mason Jun 25 '21 at 19:26
  • Plugging in wired headphones works for my use case, though. My input is a (cheap) Behringer XENYX 302 USB mixer, which is hooked up to a separate (expensive) Mac audio workstation, with various mics and guitars connected to it. The mixer can act as a standard USB audio device, so it can be the "mic" for Zoom, Meet, etc. Latency is very low—low enough for live guitar. This lets one Mac handle audio and effects processing, and serve as the input to the Mac that handles Zoom/Meet. (Presumably, this would work for streaming and live podcasting and stuff like that, also.) – Mason Jun 25 '21 at 19:35
  • AU Lab works on MacBook Air with M1 CPU using USB mic with much lower delay than the Quicktime method. (although it's compiled for Intel CPU, running under Rosetta) – Grant Nov 19 '21 at 04:29
  • I get a little bit of a computer modulated voice using this method. Any thoughts for how to correct? Thanks – joecap5 Dec 23 '21 at 19:28
  • AU Lab doesn't seem to work on my M1 mac. – Joel Croteau Jul 02 '22 at 03:55
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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.

Lri
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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
L2theL
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Bill Fraser
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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 '22 at 12:39
  • `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 08 '22 at 03:19
  • `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 08 '22 at 09:34
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Another option is "AU Lab" in Developer tools (Developer/Applications/Audio/AU Lab).

qu1j0t3
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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.

Chealion
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    Using Intel based Mac.. can't check the 'thru' checkbox.. looks like it is disabled. – Umair May 24 '15 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 '15 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 07 '17 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 '18 at 00:41
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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

cjohndesign
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  • Pro tip, unless you've got an external audio device, cover one ear when recording. It makes the delay less noticeable as you're getting the real time sound in your skull then the input after. – cjohndesign Sep 01 '20 at 17:27
  • Free version using Chrome Web Audio API: https://stackoverflow.com/questions/37326846/disabling-auto-gain-conctrol-with-webrtc-app -- at comment: https://stackoverflow.com/a/37332145/2411557 -- which mentions this Fiddle: https://jsfiddle.net/jib1/7ejwaxkc/ which can source microphone and sink to speaker. – Marc Tamsky Jan 13 '21 at 21:29
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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.

Graham T.
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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 '19 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 '20 at 20:21