The voice sounds unnatural, filtered through the interpreter program.

But I haven't done that in a long time, and it came out sounding very unnatural.

When she spoke, her voice sounded unnatural and strained, like a spring too tightly wound up.

He knew his voice sounded flat and unnatural, yet he couldn't seem to do anything about it.

She was pleading, though it sounded so unnatural coming from her mouth.

His voice sounded loud and unnatural in the echoing hall.

In the spoken language it still sounds awkward and rather unnatural.

He tried to make his voice shake as he said that, but the attempt sounded unnatural at best.

"I know him," he said, his voice sounding tight and unnatural.

My voice sounded unnatural as I tried to show only a casual interest.