Creating a Portal AI Voice
This article discusses fundemental concepts for creating new AI voiceover that has the same artificial sound as GLaDOS in Portal.
Background
Professional singer and voice actress Ellen McLain provided the voice of the AI GLaDOS throughout Portal. Several steps were undertaken to achieve the specific sound heard in the game. According to Director's Commentary in the game, McLain listened to synthesized text-to-speech voice samples to give her the general idea of how to deliver her lines. McLain then performed her lines in a monotone, robot-like manner. The lines were digitally edited, with the "pitch constrained, pitch modulation suppressed, and the formant moved up". This process is achieved through pitch correction, commonly referred to as "autotune" (though Auto-Tune is a specific brand of pitch correction software). While pitch correction is widely used to create a distinctive musical sound and correct off-pitch singing, the process can be used simply to make a voice sound more robotic and synthesized without necessarily sounding musical.
Several commercially-available sound and music editing packages include pitch correction features, which can be used to achieve this sound.
Required tools
To create a good-sounding AI voice, you will need a recording microphone and appropriate audio editing software. It is strongly recommended to use a high-quality microphone designed for recording voice or music - you will not get suitable audio quality out of a gaming headset's built-in microphone. Your audio editor will need a fully-featured pitch correction feature, with the ability to manually adjust the pitch of individual syllables.
Some software with pitch correction abilities:
- Antares Auto-Tune Evo (demo available)
- Melodyne Essential (formerly Melodyne Uno. Demo available)
- MAGIX Music Maker series (pitch correction is referred to as "Elastic Audio" in this software. Elastic audio is not featured in the demo)