Helpful Note About STANAG-4591 / MELPe HW & SW is COTS

This note in intended for Defense Contractor Management and Engineering who intend to productize MELP or MELPe vocoder (voice coder).


MELPe - Enhanced Mixed-Excitation Linear Predictive (MELP) vocoder is the latest standard for secure voice applications developed primarily for US DoD and NATO. The MELPe related software and hardware is COTS and is available in various platforms and form factors such as COTS processors or chips, boards and portable devices. Easy to integrate & maintain COTS MELPe software is available in commonly used programming languages for COTS processors in floating-point and/or fixed-point arithmetic.

But It may not be what you expect!

Some engineers who may not yet be familiar with the MELPe standard reference code might mistakenly assume that reference source code they may have access to can easily be ported to and integrated in available COTS hardware. Our conclusion from extensive debugging and improvement activities is that a highly competent and experienced DSP engineer would still require several months of time-consuming, difficult and challenging debugging and yet with uncertain outcome. We already encountered customers who initially decided to debug and port by themselves the source code that they had access to, and then contacted us again months later urgently requesting to buy our MELPe package with immediate delivery! It is noteworthy, that during our subsequent support for these customers, we realized that their DSP engineers were highly skilled and professional, and even had prior familiarity with the MELPe vocoder. So, why did that happen?


Here are some facts that managers and engineers may not realize: Compandent joined the innovative effort (led and sponsored by NSA & NATO) of creating and contributing to the development of the official MELPe standard back in 2001, following prior innovative work and contributions by excellent speech coding researchers from Texas Instruments, SignalCom (later acquired by Microsoft), and AT&T. The innovative NSA MELPe project that we participated in was aimed toward creating a proof of concept rather than a commercial product. Our official MELPe task at that time achieved its immediate goals, but with today's perspective several drawbacks have become apparent, such as:

  • the original development tools became obsolete along with their associated MELPe files, they are not supported by today standard TI's Code Composer Studio (CCS) software projects,
  • the original MELPe code was fully written in Assembly and was not C callable,
  • it did not conform to standard C environment conventions including stack usage, function calling parameters, heap usage and it still uses a small memory model,
  • Very limited real-time testing and debugging was done back then, which unfortunately missed numerous bugs and other real-time issues,
  • it takes no advantage of the newer and more advanced COTS DSP architecture,
  • it was not multi-channel and allowed for only one-channel per DSP with tons of global variables,
  • it was difficult to integrate and port to field system or commercial product.

Handling the above issues is time-consuming and is likely to take several good months even for a highly competent and experienced DSP engineer, and yet with uncertain outcome. Compandent's MELPe suite can save you the time, the risk, the uncertainty, and avoids the need to recreate what is already available as COTS.

What we did to take the MELPe package to the next level

Compandent MELPe software was used in 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. The software package has passed tests that are similar to the quality and performance tests used in the MELPe development process and/or used in Compandent's MELPe testbed. The same Compandent expertise that contributed to the official NSA MELPe standard has since continued with the development, debugging, and code enhancements at Compandent, bringing the MELPe standard reference to the next level - the Compandent MELPe suite (a.k.a MELPe++ or MELPe-Plus-Plus). Compandent has leveraged its previous experience developing MELPe components for NSA to create a reliable and compliant package that conforms with modern DSP environments & tools. It is user-friendly & easy to integrate and port to any COTS platform. Some of our contributions to create the Compandent MELPe (MELPe++) package are:

  • creating the standard CCS project for the MELPe package
  • our MELPe code was made C callable,
  • it now conforms to standard C environment conventions including stack usage, function calling parameters, heap usage and it uses large memory model having far calls,
  • we improved the code optimization,
  • more extensive tests revealed real-time bugs and other issues which we have resolved (some of which even originated from the old MELP and the C code),
  • we separated components of the MELPe package for customers that needs only parts of it,
  • we created a multi-channel packages (some are also multi-thread),
  • we had more opportunity to create a much better package that is easy to integrate and port to field system or commercial product.,
  • we created spectacular real-time demos on COTS hardware and an easy to use file processing utilities,
  • we also created COTS MELPe real-time implementation for COTS floating-point processors, and
  • we can provide you with complete software & hardware system solutions to interface MELPe and your system (modem, crypto device, etc.) and test it in real-time.

As a result, Compandent's MELPe (MELPe-Plus-Plus) package produces better quality speech than the standard reference! It is also more reliable, friendlier, and more flexible than the standard reference!

In fact, combining Compandent's MELPe++ in a system that already uses MELP (or even MELPe standard reference) on the other end is likely to improve quality on both ends! (compared to MELP or MELPe standard reference on both ends).

Compandent has also ported MELPe to various COTS processors such as TMS320c54xx, and the more advanced ones such as TMS320c55xx, TMS320c64xx C64x+ (such as C674x C672x etc.), and OMAP (c55x based, c64x+ based (L-137, L-138) etc..), and Analog Devices BlackFin ADSP-BF561 and TigerSharc (TS101, TS20x, etc.), ARM, Android, GHS PowerPC, and Microchip PIC32MZ. Compandent also created multi-channel & multi-thread COTS & POSIX compliant MELPe real-time implementation for COTS floating-point processors, and various operating systems such as Unix, Linux, Windows PC, Apple MacOS, etc...

Compandent offers low-cost Data-Terminal Equipment (DTE) such as FLEXI-232 and FLEXI-PC104 for interfacing MELPe vocoders with external devices such as Rockwell Collins MDM-3001 and other modems or crypto devices. The FLEXI-PC104 DTE are small form factor (PC-104) standalone devices made to military grade using COTS components.

Compandent has developed additional MELPe related software components such as serial communication, a proprietary robust algorithm for tracking the synchronization signaling bit in noisy channel conditions, and additional forward error correction codes (FEC).

Executive Summary

Thank you for taking the time to read this note. We continue encountering companies expending so much of its valuable resources in time and money on government, military, and other projects to recreate what is already available as COTS. Our extensive background and expertise with MELPe over a period of years, coupled with our experience with several MELPe related government projects places us in a unique position to handle your needs for MELPe. We keep up to date with new DSP techniques and developments, and we always strive to maintain compatibility with future DSP and VoIP technology. The Compandent MELPe package is easy to use and integrate, and our customer reviews provide testimonials to its high quality. We will be more than happy to answer further questions that you may have and to furnish you references. Our customers are typically more than happy to serve as our references. Compandent continues to create advanced, state-of-the art complete solutions that integrate speech coders such as MELPe with other add-on modules and functions. Dealing with Compandent means benefiting from the same world-class speech coding expertise that contributed to the creation of the official NSA/NATO MELPe standard, and continued to update and enhance it in the most professional, and reliable way!

I do believe that you want to complete your project successfully and on time, with the benefits of the best quality MELPe available. Hence I strongly recommend that you trust the experience of many demanding engineers and speech coding experts: minimize risk and maximize productivity with Compandent's MELPe suite. We are here to support you and to answer all your questions.

Please feel free to call me to discuss this further.

Oded Gottesman, Ph.D.

CTO, Compandent Inc.

What our Customers Say About US

Compandent works closely with all our customers to assist them in reaching a successful completion of their MELPe project and move forward.  You can read some of the reviews that we received from our customers, and list of partners that Compandent developed productive relationships with...