In X-Plane, open Plugins menu and click on the Plugins > PlaneCommand > Troubleshoot audio... menu item.
When speaking, the volume level should increase to approximately -30 to -5 dbFS. If this level is too low, bring the microphone closer to your mouth. You can increase your microphone gain in the Sound control panel of your operating system.
When not speaking, the sound level should be low- approximately -70 to -50 dbFS. If this level is too high, try reducing background noise like air conditioners or fans.
If the volume level does not increase when you speak, or does not change at all, continue to the next step.
Check that your microphone is working
Open the Sound control panel.
Click the Input tab.
Make sure that your desired microphone is selected. This might be "Internal Microphone" on your Mac, or an external microphone if you have a headset.
Make sure the microphone isn't muted. If you have an external microphone, there may be a physical mute switch on the microphone or on its cable.
Check that the sound level is shown. Speak, and make sure that your speech is reflected in the "Input level" meter. You might need to adjust your input volume.
Check that PlaneCommand is allowed to use the microphone
Open the Settings app.
Click on Security & Privacy.
Click on the Privacy section.
Select Microphone from the list on the left.
Ensure that X-Plane.app is checked. This will allow X-Plane and plugins like PlaneCommand to access the microphone.
Check that your sound quality is good
Sometimes noisy environments or defective microphones can cause PlaneCommand to stop working. Listening to recorded audio can help diagnose this problem.
Open the PlaneCommand audio troubleshooting window. In X-Plane, go to the Plugins menu, select PlaneCommand, and click on Troubleshoot audio...
Hold down the button you have selected to tell PlaneCommand to listen, and then give a command Press and hold the button, and say a command like "turn on the landing lights"; then release the button
Press "Play last recording".
Listen to the recorded audio. Can you hear your voice? Is there a lot of noise, or perhaps a loud hum?
Reducing background noise is one of the best ways to improve PlaneCommand's accuracy.
Use a different microphone
If you have a different microphone available, try that. Different styles and brands of microphones often have very different performance, and may provide a better experience with PlaneCommand.
Noise canceling microphones often work better. Reducing background noise is very important for speech recognition.
Built in microphones are often noisy. Audio recorded close to your computer and it's fans usually includes more noise is picked up, and that the microphone is farther from your mouth.
More expensive microphones are not necessarily better. I have tried around a dozen microphones, and found no real correlation between price and how well the various microphones work with PlaneCommand.
Moving the microphone close to your mouth is important. Being close to your mouth means your voice is louder, and background noise is quieter / farther away.
Noise canceling headset microphones are usually the best choice to use with PlaneCommand, probably for the same reason that they are so common in aviation. Personally, I use the excellent Samson Q2U when at my desk.
Update to the latest macOS
Sometimes, sound problems can be caused by bugs in audio drivers.
Follow the instructions here at apple.com to update your Mac's software.
