FS-1015

FS-1015 is a secure telephony speech encoding standard developed by the United States Department of Defense and later by NATO. It is also known as LPC-10 and STANAG 4198.

The standard was finished in 1984. The algorithm used is a linear predictive coding vocoder. The vocoder enables understandable speech, but the quality is very unnatural and synthetic. The compression rate is 20 times better than that of the MP3 algorithm.

The codec uses a bit rate of 2.4 kbit/s, requiring 20 MIPS of processing power, 2 kilobytes of RAM and features a frame size of 22.5 ms. Additionally, the codec requires a large lookahead of 90 ms.

Recently an improved version of the standard was introduced. With a longer super frame structure and better quantizer, the bit rate is reduced to 800 bit/s.

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