*Note: To convert to compatible wave before encoding with TwinVQ: 
ffmpeg -i input.flac -c:a pcm_s16le -ar 44100 output.wav

Found on:
http://www.rarewares.org/rrw/nttvqf.php

Files from:
http://www.rarewares.org/rrw/files/vqf/Tvq20001012_open_nc.zip
http://www.rarewares.org/rrw/files/vqf/in_vqf.exe
http://www.rarewares.org/rrw/files/vqf/Tvq-p215e.exe
http://www.rarewares.org/rrw/files/vqf/NTTenc.zip


Info:
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, very slow encoding, little support, no public specifications or open source implementation. 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 used for very small bitrates (8-16kbps).

A mirror of the NTT TwinVQ page is available here.
https://web.archive.org/web/20041012071040/http://www.twinvq.org/english/index_en.html

I am also mirroring Thor's page from dalnetvqf, featuring VQF plugins for Winamp. Thanks to Thor for providing these files.
http://www.rarewares.org/rrw/mirrors/vqf/index.html


FILE INFO:
    Date: 1998-03-11
    Version: 2.1.1 (encoder)
    Interface: Graphical
    Platform: Win32
    Download: NTTenc.zip - 514kB

    Date: 2000-09-22
    Version: 2.1.5 (player)
    Interface: Graphical
    Platform: Win32
    Download: Tvq-p215e.exe - 1.793kB

    Date: 2001-07-02
    Version: 1.0
    Interface: Winamp plugin
    Platform: Win32
    Download: in_vqf.exe - 419kB

    Date: 2000-10-12
    Version: 20001012
    Interface: SDK
    Platform: Win32/Linux
    Download: Tvq20001012_open_nc.zip - 3.152kB