Digital Speech Decoder (software package)

Overview

Digital Speech decoder is an open source software package that decodes several digital speech formats. It uses the mbelib library (a separate open source package) to synthesize the decoded digital speech. It does not allow decoding of encrypted communications. It can save the compressed digital audio bits to "mbe" data files (.imb and .amb extensions) and play back those saved files.

The latest version 1.1 supports the following formats and modulation types:

• P25 Phase 1
• "MoTDMA" Motorola's two slot TDMA proposal for P25 Phase 2

note: P25 Phase 2 will be different from this format when it is finalized

• C4FM C4FM modulation
• QPSK QPSK modulation (sometimes marketed as "LSM")

Other formats and modulations may be supported in future versions. DSD and mbelib should compile on Linux and *BSD operating systems. Any linux distribution should work as long as it has support for your audio devices

Copyright License

DSD and mbelib are both released under a BSD style copyright license. This means that as far as copyrighs are concerned it can be freely copied and used, including for commercial products as long as the original copyright notice is included. (however see important patent issues section below)

Patent Issues with mbelib

While DSD was intended to be patent-free, mbelib describes functions that may be covered by one or more U.S. patents owned by DVSI Inc. The source code itself should not be infringing as it merely describes possible methods of implementation. Compiling or using the code may infringe on patents rights and/or require licensing. It is unknown if DVSI will sell licenses for software that uses mbelib. If you do not have a license and are in a jurisdiction protected by the DVSI patents you should not compile or use this source code.

Downloads

dsd-1.1-src.tar	dsd-1.1-src.tar
mbelib-1.0.2-src.tar	mbelib-1.0.2-src.tar

Frequently Asked Questions

Q: Do I need a radio with discriminator tap?

A: Yes, if you want to listen live or save mbe data files. No radio or discriminator tap is required to play saved mbe data files.

Q: Will this work on Windows?

A: No, but other developers are supposedly working on a port to Windows

Q: Will this work on a Mac?

A: No, because OS X does not use the traditional unix-like /dev/audio interface. It should be easy for someone familiar with mac audio programming to port it to the Mac.

Q: Will you support decryption if I lawfully posess the encryption keys?

A: From the README file:

        Decryption of speech is NOT supported, even if you lawfully posess the
        encryption keys.  Decryption support will not be added in the future as
        the authors wish to steer as far away from the legal issues associated
        with encryption as possible.

Q: Who are the author(s)?'

A: The author(s) are anonymous but PGP keys are provided inside the packages so future releases/communications can be verified.