DualSpeech is a voice codec developed by NTT (Nippon Telephone and Telegraph, the same developers of VQF) in the mid-nineties. Quality seems good, but I own too few voice-only samples to mete out judgement.

The codec operates on mono 16bit 8kHz streams. It provides two choices of compression performance, Half Rate (3-4kbps, higher compression) and Full Rate (4-7kbps, higher quality)

The apps have a built-in expiration date because they are beta releases, so if you want to use them, you'll have to return your system clock to 1996 or 1997.

The compressed files below each contain a DualSpeech encoder, a player, and a recorder that grabs audio directly from Line-in and compresses it. The Win32 package also contains a Netscape-compatible plugin to playback DualSpeech files. The Win16 player does not seem to be capable of playing any DualSpeech stream, even the ones encoded by the Win16 encoder!

It seems development never went past these beta versions. Considering how old and obscure this vocodec is, it is no surprise that all references to it disappeared from NTT's website decades ago. But surprisingly, it is still possible to obtain archived versions of some Dual Speech pages from WNN - "World Nature Network - a homepage launched by NTT in 1995 to commemorate the 10th anniversary of its privatization".

Big thanks to William Hobbs for introducing me to this rare voice codec from NTT!


Date: 1997-06-24
Version: 0.2
Interface: Graphical
Platform: Win32
Download: DSpch32.zip - 984kB

Date: 1996
Version: 0.1
Interface: Graphical
Platform: Win16
Download: DSpch16.zip - 292kB

Date: 1997-06-24
Version: 0.2
Interface: Graphical
Platform: Mac OS Classic PPC
Download: DSpchMac.sit - 294kB