here is yamaha's answer from the same question on the arranger workstation forum.
"It has not yet been determined that there is a VH problem with the Tyros. It's been in production for over 2 years and I'm aware of 3 people worldwide that are complaining about distortion or something when using the harmonizer. I've seen and used the harmonizer many times and have not noticed a problem. Could be they're doing something quite different than we are, but we can't fix it until we can see it.

There is a cure for the USB problem, but because not all Tyros experience a problem, it's not in production as of yet. We'll be happy to update your Tyros at your convenience."

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