DOCID: 3860926
UNCLASSIFIED Cryptologic Quarter1y
(U) A History of Secure Voice Codin~: Insights Drawn from the Career of One of tile Earliest Practitioners of the Art of Speech Coding JOSEPH P. CAMPBELL, JR., and RICHARD A. DEAN
Editor's Note: This artrde Is basecl on one publlshecl In Dlgittl Signal Processing, July 1993, wfth permission ofthe authors.
The history of speech coding is closely tied to tion of PCM. A "Buzz" /"Hiss" generator was used the career of Tom Tremain. He joined the as an exciter for the vocoder corresponding to the National Security Agency i~ 1959 as an Air Force voiced/unvoiced attribute of each 20-ms speech lieutenant assigned to duty at the Agency. Llttle segment. Balance of the "Buzz" /"Hiss" generator, did he know then that this assignment would or voicing, represented a major factor in the qual shape his career as well as' the future of speech ity of the speech. Early practitioners of speech coding. 1 coders, like Tom, can still be found today speak I . ing"Aaahhh" /"Sshhhhh" into voice coders to test Thomas E. Tremain was the U.S. govern- this balance. ment's senior speech scientist. He was a recog nized leader and an expert in speech science. From the time of SIGSALY until Tom arrived 1 Tom's work spanned five dife3des of state-of-the- at NSA, several generations of voice coders had art modem and speech co<;Iing innovations that been developed in conjunction with Bell Labs. are the basis of virtually e~ery U.S. and NATO The K0-6 voice coder, developed in 1949 and modem and speech coding standard. His efforts deployed in limited quantity, was a close approx have been critical to U.S. a~d NATO tactical and imation to the 1200-bps SIGSALY voice coder. sifategicI • 51cure. commumcations• . • programs. This was followed in 1953 by the 1650-bps KY-9 I f41tor's Note: Since the original <1rtlde was pub!rshecl, shown in Figure 2. Using a 12-channel vocoder · Mr. Trem<1fn passecl Cryptologic Quarterly UNCLASSIFIED . ' I J Fig. 1. A vi~ o( SIGSALY through the ~ I i temperature, so does the sensitive tracking Coding (LPC) generation of voice coders. Tom's required between th~ speech analyzer and speech predecessors and contemporaries never quite synthesizer. Performance in the field never ,understood how the deck of punched cards he approached laborat9ry' performance; users, start- carried down the hall to a Honeywell computer I ' ing with Churchill a1nd Roosevelt [2], were reluc was ever going to result in a vocoder. Tom devel tant to use systems :that had a synthetic "Donald oped the subtle techniques necessary to load and Duck" quality. President ·Johnson refused to use invert a matrix in real time in the. fixed-point the HY-2 beclmse bf its poor quality and, as a arithmetic necessary for such an operation. A for result, deployment kas 1imited. ,, mer director of research at NSA ridiculed Tom for I suggesting such an outlandish proposal; that very 1 j , Tom's moSt: sigbificant contribution to voice method is common practice today. So that sys I coding was in· seei~ the possibilities of digital tems could run faster on the computers of the signal processing fbr voice. In an era when the day, he developed new constructs, such as the state of the art wak analog tuned circuits, Tom Average Magnitude Difference Function (AMDF) imagined a change toI computer-based processing- as a replacement for the multiply-intensive auto of speech - a radichl shift in thinking. Tom pio correlation function. Finally, in 1974 Tom . neered this new abproach, again coJlaborating demonstrated the first real-time computer simu with Bell Labs, to develop the Linear Predictive lation of LPC-10 on the CSP-30 computer, a mile- ~1 i' Page 98 UNCLASSIFIED .. DOCID: 3860926 UNCLASSIFIED Cryptologic Quarterly Fig. 2. ,The KY-9 trqns!stot!zed secure' voice : system, . citca 1953 i . J ) stone in signal processing history. This led to a whole new family of NSA vocoder products, the STU products, built around the first generation of AMD2901/TRW ~ultiplier-based high-speed bit-slice sig nal processors that forever changed the way voice coding was accomplished. Today's STU-III, shown in Figure 4, is the thjrd-generation desktop telephone that uses an enhanced LPC-10 and supports secure voice users throughout the govern ment. Voice coders, long associated only with exotic encryption schemes,'' are find ing numerous applications today for wire less communications, voice mail, and syn thetic voice applications. Today's voice I . . coders used in satellite 'communications I I I j Tom Tl'Cm Fig. 3. The HY-2 ch<1nnel voco ;1 Fig. 4. The STV-111 secure voice term!n<1I family. circa 1986 Page 100 UNCLASSIFIED ~-----~------.. -·-·· ·-·- DOCID: 3860926 UNCLASSIFIED Cryptologic Quarterly Tom was the chairman of the U.S. govern [3] on LPC is perhaps the most widely referenced , ment's Digital Voice Processing Consortium for paper in speech coding. : over twenty years. He reported directly to : the under secretary of defense for command, con Tom's later achievements were as numerous i trol, communications, and intelligence. The and important as his long-term successes. His I Consortium is the recognized U.S. government team's Code Excited Llnear Prediction (CELP) i forum for voice algorithm developments. It pro- speech coder, used in the STU-III, was endorsed 1 motes innovative research, removes duplication, as Federal Standard 1016 and proposed for a evaluates new algorithms, and promotes technol j ogy insertion. Under Tom's leadership, the · Consortium became a prestigious U.S. forum for · advancing state-of-the.,.art speech technology ; research. The Consortium activities and Tom's !personal designs have had a far reaching impact : on operational and planned communications sys- 1 terns totaling billions of dollars of national assets. ; His voice compression \VOrk facilitated high-qua] , ,ity secure communications worldwide. Senior IU.S. government officials, national communica ' tions leaders, and other senior scientists fre , quently sought his opini~ns. He instituted speech ; testing comparison standards, promoted the establishment of a worJd-recognized. r independent 1 ;test facility, initiated .inP,ovative voice compres- 1 :sion development programs, and started and To~ T~main. ~left) w.is recognized by the IEEE In monitored voice resean;h programs at universi- in~jor <;:~trl:t.i~u..,. 1 1993 \vith·a special aw.itd i-For'.his. ,·. 1 ties. Hi's original work on continuously variable tions and sustqined l~ade,rship in digital sp~e.ch c~ct- ; 1 ! slope delta modufation.\linear predictive coders, ing, mo4em technology, and V.S. and NATO stqn vocode~s, adaptive predictive coders, code excited l dards for speech coding and communi~tfon.' !41 i.}~ear ~redictors,. mo~~~- ~echnology, ~hannel i ·s1mulahon, and mtelhgib1hty and quahty test : methodology forms the :basis of most voice com NATO standard. A modified form of CELP is the : .nmnications used today. For these efforts, the basis of the algorithm used in North American . ·secretary of defense awarded. Tom with U.S. DoD digital ceJlular systems. . , ,Meritorious Civilian Service Medals in 1985 and "1992. j TolJl was also the chairman of the NATO I Narrowband Speech Working Group where he Tom chaired many ~f the IEEE ICASSP a·nd introduced low bit rate speech coders for HF I Speech Tech sessions arid was a primary organiz ECCM and VHF /UHF ECCM applications. He led . er of early ICASSP~ and Speech Coding .research in low bit rate speech coding designs by · Workshops. He personally disseminated developing vector quantization approaches using ' throughout the world the LPC source code that split codebooks and tree-based algorithms for I enabled much of today's research. He was solely fast search of large codebool, Cryptologic Quarterly UNCLASSIFIED In looking back on Tom's career, one might For further information regarding the subject point to the voice standards that he set or the of this article please contact the authors at the fol,. organizations that he chaired as a measure of his lowing email addresses: [email protected] and overall contribution. Tom would more likely have [email protected] pointed not to his own research accomplish.;. ments, but rather to the new generation of speech researchers that he mentored who still carry on his work. I . I . ~ I ,' l ~t.~ .. . 1 1 The UNCLASSIFIEDllFOR OFFICIAL USE ONLY Cryptologic Quarterly References [l] Kahn, 0. "Cryptography and the origins of [3] Tremain, T. "The government standard spread spectrum." IEEE Spectrum 21, No. 9 linear predictive coding algorithm: LPC-10." (September 1984), 70-80. Speech Technology Magazine (April 1982), 40- l 49. i [2] Doyle, M. "Private communication." October 13, 2000. The extent of actual use by [ 4] Campbell, J. "In Memory of Thomas E. Roosevelt and Churchill is still unclear and needs Tremain 1934-1995." IEEE Transactions on further research to clarify; however, there is evi Speech and Audio Processing 4, No. 1 (January dence of a call between Truman and Churchill on 1996), 1. 1:-Day (Victory in Euro~). l I I . I (U//FOUO) Jo~eph Paul Campbell, Jr., was born in Oneonta. New York, on December 20, 19~6. He received a BSEE from Rensselaer Polytechnic Institute in 1979, an MSEE from The Johns Hopkins University in 1986, and a Ph.D. in electrical enginee~ing from Oklahoma State University in 1992. He has been employed by ·· the National Security Agency since 1979. From 1979 +o 1990, he was a member of !the Narrowband Secure Voice Technology research group. His team developed 1t'e first software modem and LPC-10e, which enhanced the Federal Stan~ard 11015 voice coder and improved US and NATO secure voice sys tems. He led thej U.S. government's speech coding team in the development of th~ CELP voice coder, which became Federal Standard 1016 and is the founda tion of digital cellLlar and voice over the Internet telephony systems. From 1991 to 1998, he was ~senior scientist in NSA's Biometric Technology research group where he led voice verification research and chaired the Biometric Consortium (http://www.biom~trics.org/); the U.S. government's focal point for research, ~f I development, test, evaluation, and application biometric-based personal iden- I . tification/verificarion' technology. From 1991 ~o 1999, he was on associate edi - tor of the IEEE rransactions on Speech and Audio Processing . . I (U//FOUO) Dr. Campbell currently is a M~er Engineer in NSA's Speech . Research branchj and leads the, Acoustics Section; is a coeditor of Digital Signal Processing: A Review Journal (http://www. academicpress .com/dsp); teaches speec,h processing at The Johns Hopkins University (http://www. apl.jhu .edu/Classes/Notes/Campbell/); 2001 IEEE Distinguished Lecturer; chairs the Ellicott Mills Middle School PTA Technology Team; is a mem ber of Sigma Xi: and is a senior member of the IEEE and the Acoustical Society of America. UNCLASSIFIED//FOR OFFICIAL USE ONLY Page 103 . •, DOCID: 3860926 Cryptologic Quarterly UNCLASSIFIED (U//FOUO) Richard A. Dean received a BSEE degree from Manhattan College in 1966, an MSEE degree .from the University of Maryland in 1969 and a Ph.D. in electrical engineering from Oklahoma State University in 1990. He recently retired from NSA where he spent 33 years in the research and development of INFOSEC technology. He was a contributor to the family of Secure Telephone Units (STU) and tactical secure voice terminals developed in the 70s through the 90s. He also influenced much of the INFOSEC efforts in the development of secure wireless solutions. Mr. Dean retired from NSA in 1999 as a senior level expert. He is currently teaching electrical and computer engineering at Morgan State University. { Page 104 UNCLASSIFIED