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MELP


The MELPe (Mixed-Excitation Linear Predictive enhanced) algorithm was derived using several enhancements to the original MELP standard. It is also known as military standard MIL-STD-3005 and NATO STANAG 4591. MELP was itself derived from another military coder, LPC-10. However, MELP originally only specified a 2400 bps mode of operation. MELPe is a triple-rate low codec that supports rates of 600 bps, 1200 bps, and 2400 bps. A MELPe frame interval is 22.5 ms in duration and contains 180 voice samples, at a sampling rate of 8,000 kHz. Recommended analog requirements are for a nominal bandwidth ranging from 100 Hz - 3800 Hz. MELPe can operate with a more band-limited signal but with a degradation in performance.

MELP was selected as the new 2400 bps Federal Standard speech vocoder by the United States Department of Defense (DoD) Digital Voice Processing Consortium (DDVPC) after a multi-year extensive testing program. The selection test concentrated on four areas: intelligibility, voice quality, talker recognizability, and communicability. The selection criteria also included hardware parameters such as processing power, memory usage, and delay. MELP was selected as the best of the seven candidates and even beat the FS1016 4800 bps vocoder, a vocoder with twice the bit-rate. Advantages

MELPe is robust in difficult background noise environments such as those frequently encountered in commercial and military communication systems. It is very efficient in its computational requirements. This translates into relatively low power consumption, an important consideration for portable systems. MELPe uses extensive lookup tables and models of the human voice to extract and regenerate speech; further, the codec is tuned to regenerate the english language, and speakers of non-germanic languages generally rate the coder more poorly than english speakers.


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