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FLEXI-232 and FLEXI-422

Low-Cost MELPe Data Terminal Equipment (DTE)

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. 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. The FLEXI-232 board, illustrated in Figure 1, may be 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 (Figures 4 & 5 below), and optional Smart Lithium-Ion Battery. Compandent's specially developed sample C++ program is also available for developing your own VoIP application.

Figure 1.a Compandent's FLEXI-232 card for interfacing with external devices such as modems. (c) All rights reserved.

Figure 1.b Compandent's FLEXI-PC104 card in PC-104 form. (c) All rights reserved.

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 Figures 4 & 5 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.

Figure 5. Compandent's MELPe DTE in PlexiGlass plate enclosure and PTT switch. (c) All rights reserved.

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 and generate low-cost system solutions needed by the industry. In addition, Compandent provides various software and hardware related to the MELPe vocoder.

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 Unix, Linux, Windows PC, MacOS, 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


Customer Reviews
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5 out of 5 stars Highly Recommended!!!
Reviewer:   Project Engineer - Major Worldwide Defence Technology and Security Company (UK)

Integrating the Compandent MELPe package & FLEXI-232 DTE with our military modem device was seen as a possible risk area at the start of our project. Your first class technical support helped us immensely with our integration activities, including tailoring of the FLEXI-232 DTE firmware to meet our exacting requirements. We were up and running in less than a week of the package arriving in the UK and best of all no additional interfacing circuitry was required. Top marks!

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5 out of 5 stars Great package!!! Very professional!!!
Reviewer:   Product Manager - Defense industry (USA)

It was great pleasure doing business and working with you guys! I will be more than happy to support and recommend you. Compandent is a very professional and customer service oriented company. Your MELPe package was so easy to work with. It is a high quality software and has clear documentation. Thanks for everything, and we will support you as best we can.

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5 out of 5 stars Great product! Highly recommended!
Reviewer:   Project Manager - Secure Voice industry (Europe)

Compandent saved us many months of hard work, enabled us short time-to-market, and provided us with critical competitive advantage. Your package was very reliable, and achieved the best quality. The audio demo was very helpful for us in presenting our prototype successfully within a short period of time. It is pleasure working with Compandent. Highly recommended!

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5 out of 5 starsHigh quality software & excellent service!
Reviewer: Engineering Manager - Wireless comm. industry (USA)

Way to go Compandent! We integrated your MELPe into our product almost instantly! The Test Vector and software verification was so easy, we had almost nothing to do, it was all automatically performed, so smooth and easy. Great package which includes everything one may need for using MELPe vocoder in a product. We started with the c54xx, and in the future we will probably use the c55xx as well!

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5 out of 5 stars Excellent MELPe package, and very professional company!
Reviewer: Senior Engineer - NATO vendor (Europe)

Compandent knows the MELPe coder in-and-out! They responded promptly to any question or issue we had, and provided us with the correct answer and solution. Compandent's MELPe is very efficient computationally and memory-wise, which allowed us to run all our software on the c55xx! Definitely the best in the market. We will be more than happy to further recommend you.

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4 out of 5 stars Recommended Good Product
Reviewer: Project Manager - Wireless Device Manufacturer (USA)

This package was easy to test/verify, implement, and use on our platform. Compandent has been extremely helpful and professional with all questions and concerns. One improvement which could be made is related to the memory map. Otherwise, the product has worked exactly as expected.

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