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MELPe - Enhanced Mixed-Excitation Linear Predictive Vocoder

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. The Compandent's MELPe vocoder 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 Analog Devices BlackFin ADSP-BF561, ARM, GHS PowerPC, and Android 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.

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'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, ARM, GHS PowerPC, and Android.

The MELPe-Plus-Plus software suite includes the following features:

  • hand optimized Assembly 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
  • 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 $400) 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 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, Ground Mobile Radio (GMR) Joint Tactical Radio System (JTRS), Soldier Wave Form (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)

Condition\Coder
 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) 

 

Condition\Coder
 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) 

 

Condition\Coder
 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), TX0006874773 (melp_syn.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 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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