STANAG-4591 MELPe - Enhanced Mixed-Excitation Linear Predictive Vocoder Software

MELPe - Enhanced Mixed Excitation Linear Predictive (MELP) vocoder, known as military standard MIL-STD-3005 and NATO STANAG 4591, is a triple-rate low rate coder that operates at 2400, 1200 and 600 bps. Compandent's MELPe vocoder software suite (a.k.a. MELPe++ or MELPe-Plus-Plus) includes also compressed bit-stream transcoding between the rates as well as optional Noise Pre-Processor. MELPe's performance is demonstrated in Tables 1-3 below, and c54xx & c55xx MELPe Package Fact Sheet & c64xx / c64x+ MELPe Package Fact Sheet, as well as Windows, Linux, ARM, Android, iOS, Analog Devices BlackFin ADSP-BF561 and TigerSharc (TS101, TS20x, etc.), ARM, GHS PowerPC, and Android & iOS are also available. See also Compandent MELPe FAQ. Compandent offers low-cost Data-Terminal Equipment (DTE) such as FLEXI-232 and FLEXI-PC104 for interfacing vocoders such as MELPe with external devices such as modems. It is based on Compandent created testbed device (MELCODER a.k.a. the NATO “gold standard” reference hardware for STANAG-4591) utilized by the NATO's test-laboratory as a part of the MELPe standard adoption process.

Compandent Inc. has participated in the research, development and implementation of the Enhanced Mixed-Excitation Linear Predictive (MELPe) vocoder, and utilized its savvy expertise in speech coding and DSP to take the MELPe to the next level, the Compandent MELPe suite. In addition, Compandent provides various software and hardware related to the MELPe vocoder. Compandent MELPe software under Android was used and tested by NATO also as part of the development of Secure Communications Interoperability Protocols (SCIP).

Compandent's MELPe is better than the standard reference!

Compandent's MELPe (MELPe-Plus-Plus) produces better quality than the standard reference! Compandent has been supporting and improving the MELPe real-time implementation, and has found and fixed numerous bugs in it, many of these bugs could not be discovered by simply processing the standard Test Vectors, rather than by comprehensive process of analyzing and optimizing the code and testing it under wide variety of scenarios and conditions conducted by Compandent's speech coding and DSP experts. We can show you examples where the standard reference produces hoarse speech or annoying clicks while Compandent's MELPe (MELPe++) produces much better sounding and cleaner speech. Therefore Compandent's MELPe (MELPe++) is in fact better than the standard reference! Compandent has also greatly improved and optimized the code. Compandent has ported MELPe to various DSPs by Texas Instruments such as TMS320c54xx, TMS320c55xx, TMS320c64xx C64x+ (such as C674x C672x etc.), and OMAP (c55x based, c64x+ based (L137, L138) etc..), Analog Devices BlackFin ADSP-BF561 and TigerSharc (TS101, TS20x, etc.), ARM, GHS PowerPC and Android, iOS .

Compandent's MELPe codec software suite includes the following features:

  • STANAG-4591 NATO standard compliant
  • real-time implementation of all algorithm components
  • extensively analyzed, tested, fixed, and improved real-time implementation
  • C-callable high-level functions
  • optional components available (customer can select desired combination):
    • MELPe at 2400 bps - high rate encoder and/or decoder
    • MELPe at 1200 bps - low rate encoder and/or decoder
    • MELPe at 600 bps - very low rate encoder and/or decoder
    • compressed bit-stream transcoding between the rates
    • noise pre-processor - for reducing background noise
    • postfilter - for quality enhancement of the reproduced speech
    • multi-channel implementation
  • example of main C program that initializes and runs the MELPe vocoder functions
  • "Packetized-Network-Ready" - to maintain high quality even in severe FER conditions
  • operation mode can be switched on the fly (no need to reload the program to the DSP)
  • easy and fast Test Vectors running and verification setup
  • comprehensive and spectacular Real-Time demo, using DIP-switch control and LEDs indicators
  • comprehensive and detailed documentation that allows for smooth and easy integration
  • Compandent support and service
  • Supports Secure Communications Interoperability Protocols (SCIP) 210.
  • Optional customization adding 16 kb/s CVSD, FS-1016 4.8 kb/s CELP, FS-1015 2.4 kb/s LPC-10e, etc.
  • very low-cost (about $500) complete DSP development board and tools (CCS) on which Compandent's MELPe may run, process the Test Vectors, and spectacular real-time audio demo
  • System solution FLEXI-232 and FLEXI-PC104 : Cost-effective board and software for customized communication link to your modem or other equipment.

Compandent also provides MELPe related DSP software & hardware in various COTS form factors and platforms, including multi-channel & multi-thread POSIX (Portable Operating System Interface) compliant software running on various platforms such as Linux, Windows, MacOS, iOS, Android, IAR, ARM, Unix, Green Hills Software GHS, etc.. Such implementations are suitable for applications such as PDA, pocket PC, laptop, cell-phones, VoIP, satellite communications, secure voice, secure radio, Software Defined Radios (SDR) or software-programmable radio, STE (Secure Terminal Equipment), JTRS and MIDS terminals, Ground Mobile Radio (GMR) Joint Tactical Radio System (JTRS), Soldier Radio Waveform (SRW), Multiple Call Box (MCB), Line Replaceable Unit (LRU). Defense Contractors, please also refer to: Note to Defense Contractor Management and Engineering.

For details contact us, Download MELPe Package Fact Sheet MELPe Package Fact Sheet in PDF format , Compandent MELPe FAQ

MELPe - Audio Samples: (click to play)

 

Coder / Condition Original 600 bps 1200 bps 2400 bps
Clean Original 600 bps 1200 bps 2400 bps
Noisy Original 600 bps 1200 bps 2400 bps

Table 1. Audio samples of Compandent's 600/1200/2400 bps MELPe (including Noise Pre-Processor)

 

Coder / Condition 600 bps 1200 bps 2400 bps
Clean 600 bps 1200 bps 2400 bps
Clean - 1% FER 600 bps 1% FER 1200 bps 1% FER 2400 bps 1% FER
Clean - 3% FER 600 bps 3% FER 1200 bps 3% FER 2400 bps 3% FER
Clean - 5% FER 600 bps 5% FER 1200 bps 5% FER 2400 bps 5% FER
Clean - 10% FER 600 bps 10% FER 1200 bps 10% FER 2400 bps 10% FER
Clean - 20% FER 600 bps 20% FER 1200 bps 20% FER 2400 bps 20% FER
Table 2. Audio samples of Compandet's 600/1200/2400 bps MELPe in various Frame Erasure Rates (FER)

 

Coder / Condition 600 bps 1200 bps 2400 bps
Noisy 600 bps 1200 bps 2400 bps
Noisy - 1% FER 600 bps 1% FER 1200 bps 1% FER 2400 bps 1% FER
Noisy - 3% FER 600 bps 3% FER 1200 bps 3% FER 2400 bps 3% FER
Noisy - 5% FER 600 bps 5% FER 1200 bps 5% FER 2400 bps 5% FER
Noisy - 10% FER 600 bps 10% FER 1200 bps 10% FER 2400 bps 10% FER
Noisy - 20% FER 600 bps 20% FER 1200 bps 20% FER 2400 bps 20% FER
Table 3. Audio samples of Compandent's 600/1200/2400 bps MELPe in various Frame Erasure Rates (FER)

Please note: Compandent owns intellectual property (IP) in the official (standard) MELPe implementation, and any of its derivatives (see for example USCO certificate of copyright registration numbers: TX0006703781 (postfilt.asm), TX0006845325 (lpc_lib.asm), TX0007161044 (lpc_lib.c), , and many more. Any party intending to develop commercial products based on MELPe should contact Compandent as well as other IP holders regarding licensing.

To report bugs or suggestions to the MELPe algorithm implementation please mail to: MELPeSupport@compandent.com

MELPe Software Platforms Samples

Compandent's highly optimized and enhanced MELPe vocoder software is already available on many platforms, some of which are listed below. Compandent keeps porting it to new platforms.  Please contact us for specific platform implementation.

platforms1
platforms2
Platforms3

MELPe Hardware...

MELPe hardware is also available for quick integration...