Why does Mac dictation not work with an external microphone?

Mac dictation usually ignores an external microphone for one of two reasons: the Mac is listening to a different input, or the microphone's input volume is too low for the Mac to hear you. Dictation has its own Microphone source menu, and on Automatic the Mac listens to the device it thinks you are most likely to use ( ¹). Choose your microphone there, check its input volume in Sound settings, then test one sentence in Notes. Most cases end at one of those steps, and none of them needs a change to macOS security.

Select the external microphone before you check anything else

Apple's troubleshooting for Dictation starts with the microphone itself. If your Mac has no internal microphone, Apple says to make sure an external microphone is "connected to your Mac and selected in Sound or Keyboard settings" ( ²). Without that step, Dictation has nothing to listen to. Apple lists this check among several for Dictation that does not work as expected, next to the language, the shortcut and your internet connection ( Apple's Dictation troubleshooting page).

Automatic can keep listening to a device you are not speaking into

Automatic is the cause that is easy to miss. A Mac can use several inputs: the internal microphone, a display's microphone, an iPhone microphone, or an external microphone plugged into the sound port ( Apple's sound input settings page). Because Automatic follows the device you are most likely to use, it can keep listening to another input while your external microphone sits on the desk. Setting Microphone source to your microphone by name removes the guess.

A headset works only when it has its own microphone

Apple describes the sound port as a port that takes mono input from a headset with a built-in microphone: ³. Headphones with no microphone give the Mac an output and nothing to listen with, so Dictation has no input to use. If a headset is plugged in and Dictation still ignores it, open Sound settings and check whether the headset appears in the Input list. If it does not appear, the connection is the problem, not Dictation.

Low input volume makes a working microphone sound silent

Apple's troubleshooting page says that if you use an external microphone, "make sure its input volume is sufficient" ( ⁴). Apple does not give a number for sufficient, so judge it by the result. Choose Apple menu > System Settings, click Sound in the sidebar, click Input, select the microphone, and drag the input volume slider. Then dictate one sentence at your normal speaking volume. If the words appear, the level is enough. If nothing appears, raise the level a little more and test again.

Distance and noise can defeat a good external microphone

A microphone that is connected and selected still has to be close to your mouth. In a 2017 study of distant speech recognition, close-talking sentences recorded in a studio had a word error rate of 3.7 percent ( ⁵). A single distant microphone in a real apartment had a word error rate of 12.0 percent ( ⁶). That recognizer was a 2017 research system, not Apple's, so read the numbers as a direction and not as Apple's measurements. The direction is clear: the farther the microphone, the more words come out wrong.

Apple's advice points the same way. If you dictate in a noisy environment or a room with excessive echo, Apple says it may help to use a headset microphone ( ⁷). A headset sits close to the mouth, which is the point of the advice.

A Bluetooth microphone can switch to a lower-quality mode

If the external microphone is a Bluetooth headset, its quality changes while it is in use. Apple says Bluetooth has two modes, and that when it switches to the second, audio quality is reduced until the microphone is no longer in use ( ⁸). A headset that sounds fine on a call can therefore be a weak input for Dictation. To test, choose a wired or built-in microphone in Microphone source and dictate the same sentence again.

When the microphone still fails, the symptom points to the cause

What to do, in order

1. Connect the microphone, then open System Settings, click Sound, and click Input. Confirm the microphone is in the list.
2. Open System Settings, click Keyboard, go to Dictation, and choose the microphone in the Microphone source menu. Our question on how to change the microphone Mac dictation uses gives the full steps.
3. In Sound settings, select the microphone and drag the input volume up if your test sentence does not appear.
4. Click into a blank note in Notes, start Dictation, and say one full sentence at a normal volume.
5. If Notes works and another app does not, check that app's microphone access. If the text stops whenever you pause, read why Mac dictation keeps stopping.

If the microphone works in every test and dictation still fails, the cause is more likely the switch, the language or a restriction. Our guide to why Mac dictation is not working covers those checks in order, and the question on the wrong language covers the language check.