If you ever listen to people try to record sound that's clear and precise, they actually sound fairly robotic. See this Google 20% Project where they explore Google Assistant's voice creation: https://youtu.be/qnGNfz7JiZ8?t=5m23s

WaveNet is probably modeling the source data very well. It sounds like they just need more data with emotion and inflection, rather than having source data that is optimized for monotonicity and precision.

Great video!

If you work in radio or voiceover you learn really quickly that the voice is so much more complex than people give it credit for. Subtle changes in delivery, timing, inflection, syllabic emphasis, pauses etc... make a massive difference.

Anyone can "talk like a robot" but speaking naturally is way more dynamical than just making the sounds of the words transition smoothly.

I'm not sure if it's way easier or way harder than we're doing it now.

The improved voices sound exactly like the audio from CBT's I've taken in the past. Could possibly have fooled me.

What is CBT?

CBT is commonly understood to mean Cognitive Behavioral Therapy, but in this case I believe OP means computer based training(s?)

Computer-Based Training

Perhaps I'm just less demanding but I was pretty blown away. Perhaps it sounds robotic but it's coming from the same voice recording. The main difference was how perfectly the words blend together. Now I'm just waiting to get Stephen Fry samples instead.

The Japanese one is miles ahead of the previous one however.

I guess the hope is that even if it doesn't sound much better, this will open new doors, such as being able to iterate faster on new languages, new voices and new speaking styles (singing, whispering, etc).

EDIT: A big example of that is the Japanese example at the bottom. English has had far more effort put into the old model, so it's already pretty good. But the difference between the old and new Japanese voice is really striking, and they were most likely able to make the new one much faster.

I thought it's just me. I remember the first WaveNet demo sounded significantly more natural than the non-WaveNet stuff. But now they sounded almost the same. The main difference is that with WaveNet you don't hear that robotic tone at the end of a phrase, that's typical of old TTS technologies. But the way the phrase is spoken still sounds like a machine said it, rather than a human.

I wonder what compromises they made to improve the performance by 1,000x. There have to be some.