From Hydrogenaudio Knowledgebase
TwinVQ is an audio encoding technology developed at NTT (Nippon Telephone and Telegraph). It uses an unique technology called Vector Quantization (VQ) for encoding.
The format using the TwinVQ technology is called VQF. There are several limitations in this format: 2 channels at most, no VBR, extremely slow, few support. It can pretty safely be considered dead these days.
TwinVQ, on the other hand, is still alive as part of the MPEG4 audio standard, being featured at extremely small bitrates (8-16kbps).
At some point during late nineties, Yamaha bought the VQF technology from NTT and created their own encoder, SoundVQ.
It has features like batch encoding and recording from line-in. Quality in high quality mode is reasonable, but encoding is extremely slow. Also, it only works for 90 days then expires.
Yamaha discontinued offering their SoundVQ software line after the obvious failure of the format in becoming popular.