Whether you're a fan of the epic clash of Autobots versus Decepticons, a Mass Effect fanatic, or otherwise, I doubt anyone who heard Optimus, Megatron, or Sovereign speak could hold back the "holy shit!" instantaneously birthed at the sonaural awesome bashing them in eardrums. You'd almost think these guys were real, cool robots, but the truth is, these synthetic life forms' voices were accomplished with vocoders.

What is a vocoder? I'll put it in laymans terms. A vocoder takes one sound and uses it to filter another, i.e. using the audio of a spoken line to filter a desired sound. The result, the voice now sounds as if it IS the sound. Robots in games are often portrayed through this method, such as Sovereign in Mass Effect and Legion in Mass Effect 2 and 3.

Vocoders are usually prohibitively expensive, with on exception, Audacity, which is free. Download it and any additional files you may need for .mp3 export, etc.

Now, record your voice and select the sound you want it to emulate. This is best done with a simple bass note, as any pulsing will come through the final result.

Import them into Audacity. Pan the vocal track left and the other track right.

Set volumes as needed to make sure there is no clipping. You may want to use noise cancellation on the vocal track.

Cut away excess audio that you don't want included, and trim silence.

Select both tracks. Under the "Tracks" tab, select "Mix and Render"

The result will be one track, vocals left, sample right. Now select under "Effect", "Vocoder"

Preview. If you don't like it, fiddle with the settings until you do.

Voila, free robot voice for you! You might even be able to sound like this.