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Digital Speech Decoder (software package)

From The RadioReference Wiki

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 1.3 supports the following formats and modulation types:

  • P25 Phase 1
  • ProVoice EDACS Digital voice
  • X2-TDMA - Motorola public safety TDMA system with P25 style signaling (mostly based on DMR)
  • DMR/MOTOTRBO - Digital Mobile Radio standard
  • C4FM modulation
  • GFSK modulation (including GMSK and other filtered 2/4 level FSK)
  • QPSK modulation (sometimes marketed as "LSM")

The following formats are currently under investigation or development:

  • OpenSky - Need signal samples, four slot format vocoder may be supported by mbelib
  • NXDN - 9600 baud frames recognized, vocoder is supported by mbelib, no voice yet
  • P25 Phase 2 - standard not finalized yet, vocoder is supported by mbelib
  • D-STAR - Voice frames recognized, vocoder not supported by mbelib

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. DSD version 1.3 and later requires mbelib 1.2 or later.

Copyright License

DSD and mbelib are both released under a BSD style copyright license. This means that as far as copyrights 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 mbelib 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-1.3-src.tar

dsd-1.3-src.tar

mbelib-1.2.1-src.tar

mbelib-1.2.1-src.tar

Known Working Hardware Setups

Template:Prettytable |-align="left" style="background:silver;" ||Discriminator Source||Input||Input Sound Device||Output Sound Device||Linux Flavor||Computer Specs||Audio Successfully Decoded |- |Pro-2067 direct tap||Line In||Analog Devices ADI 198x Integrated Audio||Analog Devices ADI 198x Integrated Audio||Ubuntu 10.4||Dell GX520||mototrbo and provoice |}

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.