Using Loopback and MacOS Dictation to transcribe audio from files

MacOS includes a powerful Dictation feature, which can transcribe spoken words to audio. However, this feature is only built for live audio, brought into the Mac via a microphone. On its own, the OS's Dictation system doesn't alow you to transcribe from pre-recorded audio files.

Fortunately, the addition of Loopback makes it possible to transcribe from audio files. Loopback can route audio from a playback application into the Mac's built-in dictation system, which will then transcribe the audio. This article lays out the process.

Create a Loopback virtual audio device

To begin, you'll create a Loopback virtual audio device, which will route the audio you want transcribed into the Mac's Dictation system.

  1. Click the New Virtual Device button to create a new device, and give it a descriptive name, like “Transcription Device”.

  2. You won't use the Pass-Thru source which is included by default, so remove it by clicking to highlight it, then pressing the Delete button.

  3. Add the application you'll be using to playback your source audio file by clicking the (+) button next to the Sources header.

    For this example, we'll use “QuickTime Player” to playback the audio file we want to transcribe.

With the device now configured, you can actually quit Loopback. Even with the Loopback application closed, this virtual device will still be present and available on your system.

Configure Dictation's input device setting

Once you've created your virtual device, you need to set it as the input for Dictation.

  1. Click the Apple menu in the upper left of your screen, then select System Preferences.

  2. Click the Keyboard icon, then the Dictation tab.

  3. Here, you need to click the menu under the microphone on the left side, and select the virtual device created in the step above.

    Here, “Transcription Device” has been configured for input.

Prepare your text editor

You'll need to use a text editor, such as MacOS's built-in editor TextEdit, for your transcription. start Dictation. Open your text editor, and create a new document. This is where you'll have MacOS transcribe your audio to text.

Set up your audio for playback

Next, you'll get your source audio read to play. Here, a test audio file has been opened in QuickTime Player. When that audio is played, it will pass through the virtual audio device (“Transcription Device”).

Start Dictation

You're now ready to begin with your transcription. Start the audio playing in QuickTime Player, then switch to TextEdit and select Start Dictation from the Edit menu. The Dictation popover will appear, and audio played in QuickTime Player will be passed to it, resulting in the audio being transcribed to text.

Wile Dictation is running, you won't hear the audio being played. If you wish to hear audio as it's transcribed, see Appendix A: Monitoring audio during transcription.

When the audio has finished playing, click the Done button in the Dictation popover to stop dictation.

That's it! You'll now have transcribed text in your text editor, ready for you to edit, save, and use.

Appendix A: Monitoring audio during transcription

While Dictation is running, the OS mutes the default output device, which results in playback not being audible by default. If you wish to hear the audio as it's transcribed, you can work around this with a secondary audio output. Simple USB audio adapters are readily available for around $10, in both USB-A and USB-C form factors, and work well for this.

Once you have a secondary audio device connected to your Mac, you can adjust your Loopback device to include a monitor, as seen below. MacOS will not mute output to this secondary device, so you'll be able to hear the audio as it plays.