Launch Audacity. Open the "File" menu and hover the mouse over "Import." Click "Audio."

Navigate to the vocal recording to which you want to apply the Audacity vocoder. Double-click the file to load it into Audacity. Click "OK" if Audacity asks you to confirm the import method.

Open the "Tracks" menu. Click "Stereo Track to Mono" to convert the imported audio to a mono track. Open the "Tracks" menu again, hover the mouse over "Add New" and click "Audio Track." Audacity will create a new mono audio track underneath the vocal.

Open the "Generate" menu and select "Tone." Set the "Waveform" to "Sawtooth." Click "OK." Audacity will generate a carrier waveform for the vocoder to use.

Click the down arrow next to the name of the vocal in the upper-left corner of the Audacity mixer window. Click "Make Stereo Track" to join the vocal and the generated tone.

Open the "Effect" menu and scroll down to the bottom of the list of effects. Click "Vocoder" to open the vocoder plug-in.

Adjust the "Number of Vocoder Bands" slider in the vocoder plug-in window as desired. The more bands you use, the smoother the vocal will sound; however, a high number of bands will also greatly increase the effect's processing time.

Click "OK" to apply the vocoder effect. Click "Play" to listen to the vocoded vocal.