FIPS 137, originally issued as FED-STD-1015, is a secure telephony

speech encoding Speech coding is an application of data compression of digital audio signals containing speech. Speech coding uses speech-specific parameter estimation using audio signal processing techniques to model the speech signal, combined with generic da ...

standard for

Linear Predictive Coding Linear predictive coding (LPC) is a method used mostly in audio signal processing and speech processing for representing the spectral envelope of a digital signal of speech in compressed form, using the information of a linear predictive model. ...

vocoder A vocoder (, a portmanteau of ''voice'' and ''encoder'') is a category of speech coding that analyzes and synthesizes the human voice signal for audio data compression, multiplexing, voice encryption or voice transformation. The vocoder was ...

developed by the

United States Department of Defense The United States Department of Defense (DoD, USDOD or DOD) is an executive branch department of the federal government charged with coordinating and supervising all agencies and functions of the government directly related to national secu ...

and finished on November 28, 1984. It was based on the earlier STANAG 4198 promulgated by

NATO The North Atlantic Treaty Organization (NATO, ; french: Organisation du traité de l'Atlantique nord, ), also called the North Atlantic Alliance, is an intergovernmental military alliance between 30 member states – 28 European and two No ...

on February 13, 1984. FED-STD-1015 was re-designated as ''Federal Information Processing Standard'' ( FIPS) Publication 137, (FIPS PUB 137) on October 20, 1988. It is also known as "LPC-10". The

codec A codec is a device or computer program that encodes or decodes a data stream or signal. ''Codec'' is a portmanteau of coder/decoder. In electronic communications, an endec is a device that acts as both an encoder and a decoder on a signal or da ...

uses a bit rate of 2.4 kbit/s, requiring 20 MIPS of processing power, 2 kilobytes of

RAM Ram, ram, or RAM may refer to: Animals * A male sheep * Ram cichlid, a freshwater tropical fish People * Ram (given name) * Ram (surname) * Ram (director) (Ramsubramaniam), an Indian Tamil film director * RAM (musician) (born 1974), Dutch * Ra ...

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 VQ quantizer, the

bit rate In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time. The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction w ...

is reduced to 800 bit/s.

References

External links

CELP-3.2a and LPC-10

LPC10 presentation, Soo Hyun Bae, ECE 8873 Data Compression & Modeling, Georgia Institute of Technology, 2004
Speech codecs {{US-gov-stub