Jessie Levine smiles and shakes her head when she hears the outgoing voicemail message on her iPhone.

“I sound young! And fast!” she marvels. “That person never, ever expected to talk like this.”

The message was recorded before Levine was diagnosed with Lou Gehrig’s disease, or ALS, in early 2015, and before the progressive motor neuron disease caused her speech to become slow and slurred. But as her ability to talk deteriorates, she’s exploring a new way to restore her voice via speech synthesis, or the artificial production of human speech.

The technology has been around for decades, but as devices shrink in size, efforts to customize them are expanding. Multiple companies and research groups are using speech synthesis engines to create voices from spoken samples, usually thousands of recorded sentences.