MELCODER – NSA & NATO’s MELPe Test-Bed

The “Gold standard” reference hardware for STANAG-4591

Compandent was contracted by NSA (who lead and funded the MELPe R&D and standardization) to develop and deliver the MELPe “Gold standard” reference hardware for STANAG-4591, a.k.a. MELCODER. It was utilized by the NATO’s test-laboratory as a part of the MELPe standardization process. Its software conformed with all the MELPe standard’s requirements. MELCODER provided real-time implementation of MELPe, panel mount user’s control for selecting the different MELPe features, and LED indications for real-time MELPe status monitoring. It included audio IO, and serial link for compressed bitstream IO. It can be connected to any testing device, or field channel for real-time testing of the MELPe vocoder under various conditions. The MELCODER was used by the NATO’s test laboratory that evaluated the MELPe and confirmed its performance under numerous conditions.

Figure 1.a Compandent’s MELCODER (front) The MELPe “Gold standard” reference hardware for STANAG-4591. (c) All rights reserved.
Figure 1.b Compandent’s MELCODER (rear) The MELPe “Gold standard” reference hardware for STANAG-4591. (c) All rights reserved.

Today Compandent offers low-cost Data-Terminal Equipment (DTE) for interfacing vocoders (such as MELPe) with external Data Communication Equipment (DCE) such as modems or crypto devices. For example, Compandent’s Flexible-Link for EXternal Instrument using RS-232 (FLEXI-232) or RS-422 (FLEXI-422) is a low-cost card that can be used as DTE connected to various external devices such as modems or crypto device using RS-232 or other protocols. It is easy to use, just plug it and play, and comes with optional Push-To-Talk (PTT) switch, and Smart Lithium-Ion Battery for your convenience. The FLEXI-232 board, illustrated in Figures 3 & 4, mounted to DSK board (such as the DSK5416, DSK5510, DSK6416 and various OMAP, such as OMAP1xx, OMAP2xx, OMAP3xx, OMAP4xx, and L-13x), or PC-104 DSP board that runs vocoders such as MELPe, G729, G723.1, etc.. The FLEXI-232 is an extremely versatile board that can be programmed to handle any required standard or customized communication protocol (beyond what a typical DSP may be capable of) including MIL-STD-188-114, RS-232, RS-422, RS-423, USB, TCP-IP Ethernet, 802.11b/g Wireless, etc.. It also has user friendly control and set-up interface. In addition, the FLEXI-232 has general purpose I/O lines that can be customized to your special needs. It can be also delivered as a standalone portable device in appropriate enclosure (Figure 4 below), and optional Smart Lithium-Ion Battery.Compandent’s specially developed sample C++ program is also available for developing your own VoIP application.

Block diagram of voice via DTE and modem / DCE system is illustrated in Figure 2.a, and VoIP application example Figure 2.b. Compandent offers such a low cost MELPe-DTE that can interface with Rockwell-Collins MDM-3001 modem for example (Figure 3).

Figure 2.a Block diagram of voice via FLEXI-232 DTE and modem / DCE system. (c) All rights reserved.

Figure 2.b Block diagram of VoIP system example using FLEXI-232 DTE. Compandent’s specially developed sample C++ program is available. (c) All rights reserved.

The FLEXI-232 MELPe-DTE features:

  • Low cost MELPe data terminal (may also include other vocoders such as CVSD, CELP (FS-1016), LPC-10 (FS-1015), G729, G723.1, GSM, etc.)
  • User friendly and is easy to use, just plug it and play
  • Compatible with Rockwell-Collins MDM-3001 modem,
  • Can interface with any required standard or customized protocol, synchronous and/or asynchronous (serial RS-232, RS-422, RS-423, USB, TCP-IP Ethernet, 802.11b/g Wireless, etc.), and perform processing for networks such as GSM, CDMA, TDMA, 3GPP, 3GPP2, etc.
  • Form factor: OEM board, PC-104 (plus) form, or Standalone portable device with optional high quality enclosure (see Figure 4 below). Metal enclosure dimensions are 47 x 120 x 235 mm = 1.85″ x 4.70″ x 9.25″, and about the same for the PlexiGlass economy enclosure.
  • Optional MELPe 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
  • Full-duplex (half duplex is also possible)
  • Robust synchronization even in noisy channel conditions
  • Various bit packing formats
  • Allows for independent receive and transmit clocks
  • Auto-detection of connected modem’s bitrate
  • “Packetized-Network-Ready” – to maintain high quality even in severe FER conditions
  • Optional Push-To-Talk (PTT) (optional bleep insertion)
  • Optional analog bypass or sidetone insertion (useful for telephony and headset applications)
  • Audio input and output (on DSK), and volume adjustment
  • Develop your own VoIP application using helpful specially developed sample C++ program by Compandent.
  • Operation and functionality can be switched on the fly
  • General purpose IO connector
  • Watchdog timer for providing a very robust system (in PC-104 only)
  • Optional standalone device using Smart Lithium-Ion Battery
  • Optional connectors such as DB25, DB9, Ethernet, Wireless 802.11b/g antenna module, etc.
  • Additional RS-232 port for communicating with host PC (useful for debugging)
  • Various DSP such as c5416, c5510, c6416 OMAP, DaVinci etc.
  • Easy control and status interface using push-button switches, DIP-switch, and LEDs indicators
  • Comprehensive and detailed documentation that allows for smooth and easy hook-up and operation
  • Compandent’s excellent support
  • Very low-cost (about $400) complete DSP development board and tools (CCS)
  • Customized System solution: Cost-effective board and software for customized communication link to your modem or other equipment.
  • Also avaiable Economy Option: cable for directly communicating two DSK boards (i.e. without modem and daughtercard)
  • Lead-Free RoHS compliant.

Figure 3. Compandent’s MELPe DTE connected to Rockwell-Collins’ MDM-3001, microphone and headphone. (c) All rights reserved.

Figure 4. Compandent’s MELPe DTE in high quality custom metal enclosure and PTT switch. Metal enclosure dimensions are 47 x 120 x 235 mm = 1.85″ x 4.70″ x 9.25″, and about the same for the PlexiGlass economy enclosure. (c) All rights reserved.

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.

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 PC, Android, iOS, MacOS, ARM, DSP, GHS, TI, Analog Devices, 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. 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

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 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

Note To Defense Contractor Management and Engineering

This note in intended for Defense Contractor Management and Engineering who intend to productize MELP or MELPe vocoder (voice coder).  To learn more about Compandent’s MELPe software suites and hardware… Helpful Note About MELPe