The ATR3350iS lav mic comes with a special splitter, with TRRS plug that can work with a smartphone... and presumably a MacBook. Not so, out of the box. Here's a workaround I discovered.
This version of the ATR-3350 came with the "smartphone adapter" splitter, which has a TRRS plug (for a smartphone or MacBook) on one side, and 2 jacks for headphones and mic on the other.
This is what I bought: http://www.audio-technica.com/cms/wir...
However, using the splitter to connect only a lav mic to the MacBook didn't work for me. Lav mic to splitter to MacBook didn't work; the Mac's built-in mic remained the active device.
Fortunately I found a workaround.
Here is a demonstration of my technique that uses a standard Apple "EarPods with Remote and Mic" with the audio-technica equipment, to get the Mac to receive input signal from the lav mic.
(The exact Apple product I used "EarPods with Remote and Mic," model # MD827LL/A. This was a $35-ish version I picked up at Staples.)
My machine is a MacBook Pro (Retina, 13-inch, Early 2015). I'll be referring to the single 1/8" jack on the side labeled with the headphones icon as the "audio out port".
The goal is to get the Mac to switch its audio input source from "Internal Microphone / Built-in" to "External Microphone / Microphone port".
1. (optional, but recommended) open the Sound preferences panel, and click on the Input tab to monitor what's happening with your input devices.
(Note: please ignore the "Soundflower" devices shown in this recording. Those are from installed software that has nothing to do with this technique.)
2. Start with nothing plugged into the Mac's audio out port.
3. Plug the Apple EarBuds with Mic into the HEADPHONE jack of the splitter.
4. Plug the splitter into the MacBook. You should see the input device change in the Sound Preferences dialog to "External Microphone / Microphone port".
If you don't see this device change, then this technique probably won't work, I'm sorry to say. This was the critical part I stumbled across that got things to work: finding a way to trigger that device switch.
5. With the input device showing "External Microphone", now plug the audio-technica lav mic into the MIC input of the splitter.
6. Turn on power to the lav mic, and you should now start receiving signal from the lav mic, not the MacBook built-in mic. Success!
7. One final note -- if you unplug the SPLITTER, you cannot just plug it back in. The input device reverts to Internal Microphone, and, it will NOT re-recognize the equipment as before.
You need to re-do the procedure starting with ONLY the EarBuds plugged into the splitter, when the splitter is first inserted into the MacBook.
###
Hope this helps folks! And please -- if this exact procedure does NOT work for you, please share info about your exact Mac model and O/S, and the equipment you used. Maybe there's still a way to get it to work. Thanks.
P.S. I originally discovered this trick with a different external headset & mic, something like a "Vansonic Microphone / Headphone for PC Computer Laptop". In that case, I found that having only the MIC from that device plugged into the MIC jack of the splitter, when the splitter was inserted into the MacBook, that the Sound input device switched from Internal to External. (That's right, in this case an item plugged into the MIC jack, not the HEADPHONE jack as in the procedure above.) Go figure! At this point, i unplugged the Vansonic mic (from the splitter) and inserted the lav mic... And THAT worked.
But since my headset is of unknown make, I went and bought standard Apple EarBuds this afternoon to ensure there was a pure Apple approach I could report here. But then that didn't exactly work the same way as the Vansonic. Instead, it was the HEADPHONE jack on the splitter that needed to have the the EarBuds initially plugged into, before plugging the splitter into the Mac. How weird is THAT?
Sooo... bottom line... play around with different combinations if what I've reported doesn't work for you. There's just something special about what Mac needs to "detect", for Microphone device to switch from Internal to External. And once you figured a way to trigger that, THEN you can plug your lav mic into the MIC jack of the splitter.
Cheers and Good Luck!