Milestone-Proposal:Line spectrum pair (LSP), an essential technology for high-compression speech coding, 1975
This proposal has been submitted for review.
Is the achievement you are proposing more than 25 years old? Yes
Is the achievement you are proposing within IEEE’s fields of interest? (e.g. “the theory and practice of electrical, electronics, communications and computer engineering, as well as computer science, the allied branches of engineering and the related arts and sciences” – from the IEEE Constitution) Yes
Did the achievement provide a meaningful benefit for humanity? Yes
Was it of at least regional importance? Yes
Has an IEEE Organizational Unit agreed to pay for the milestone plaque(s)? Yes
Has an IEEE Organizational Unit agreed to arrange the dedication ceremony? Yes
Has the IEEE Section in which the milestone is located agreed to take responsibility for the plaque after it is dedicated? Yes
Has the owner of the site agreed to have it designated as an Electrical Engineering Milestone? Yes
Year or range of years in which the achievement occurred:
Title of the proposed milestone:
Line spectrum pair (LSP) for high-compression speech coding, 1975
Plaque citation summarizing the achievement and its significance:
Line Spectrum Pair, invented at NTT in 1975, is an important technology for speech coding. A speech synthesizer LSI was designed based on LSP in 1980, and many international speech coding standards of ITU-T (IP phones), 3GPP, 3GPP2 (3rd generation cellular phones), and the Internet Engineering Task Force have adopted LSP as an essential technology. These standards cover almost all cellular and IP phones worldwide.
In what IEEE section(s) does it reside?
IEEE Tokyo Section, Japan
IEEE Organizational Unit(s) which have agreed to sponsor the Milestone:
IEEE Organizational Unit(s) paying for milestone plaque(s):
Unit: IEEE Tokyo Section, Japan
Senior Officer Name: Senior officer name
IEEE Organizational Unit(s) arranging the dedication ceremony:
Unit: IEEE Tokyo Section, Japan
Senior Officer Name: Senior officer name
IEEE section(s) monitoring the plaque(s):
IEEE Section: IEEE Tokyo Section, Japan
IEEE Section Chair name: Section chair name
Proposer name: Takehiro Moriya
Proposer email: Proposer email
Street address(es) and GPS coordinates of the intended milestone plaque site(s):
NTT Musashino R&D center 9-11, Midori-cho 3-Chome Musashino-Shi, Tokyo 180-8585 Japan
Describe briefly the intended site(s) of the milestone plaque(s). The intended site(s) must have a direct connection with the achievement (e.g. where developed, invented, tested, demonstrated, installed, or operated, etc.). A museum where a device or example of the technology is displayed, or the university where the inventor studied, are not, in themselves, sufficient connection for a milestone plaque.
Please give the address(es) of the plaque site(s) (GPS coordinates if you have them). Also please give the details of the mounting, i.e. on the outside of the building, in the ground floor entrance hall, on a plinth on the grounds, etc. If visitors to the plaque site will need to go through security, or make an appointment, please give the contact information visitors will need.
Initial invention, follow up investigations and developments have been carried out at this site.
Are the original buildings extant?
No. New building has been built on the original site.
Details of the plaque mounting:
The plaque will be placed near the reception area in the ground floor entrance hall. All visitors have free access to this hall.
How is the site protected/secured, and in what ways is it accessible to the public?
NTT’s receptionists are always near the plaque, and the plaque will be displayed in a transparent hard case.
Who is the present owner of the site(s)?
NTT (Nippon Telegraph and Telephone) corporation
A letter in English, or with English translation, from the site owner(s) giving permission to place IEEE milestone plaque on the property:
A letter or email from the appropriate Section Chair supporting the Milestone application:
What is the historical significance of the work (its technological, scientific, or social importance)?
The line spectrum pair (LSP), invented in 1975, is one of the most efficient feature representation technologies for speech signals. Due to its number of practical merits for high-compression speech coding, it is commonly used worldwide in speech coding standards for cellular and IP phones, including 3GPP AMR (3G cellular in Europe and Japan), 3GPP2 EVRC (3G cellular in the USA and Japan), ITU-T G.723.1 and G.729 (IP phones), IETF SILK (software IP phones, Skype) , and PDC half (2G cellular in Japan), which cover almost all high-compression telephone communications systems that are widely used around the world now and will be in the future.
What obstacles (technical, political, geographic) needed to be overcome?
Auto-regressive linear prediction coding (LPC) technology is one of the most powerful and useful speech coding tools . Pioneering investigations of the technology were independently and simultaneously started by Dr. B. S. Atal and Dr. M. R. Schroeder at AT&T Bell Labs in 1966, and by Dr. F. Itakura and Dr. S. Saito at NTT (Nippon Telegraph and Telephone) Labs. Representation and quantization of the prediction coefficients with less bit consumption and smaller LPC spectral distortion are the most critical issues in the LPC framework. At the same time, speech coding for cellular phones needs to be robust against transmission bit errors in the radio-wave environment. Thus, the representation method of predictive coefficients needs to achieve smaller LPC spectral distortion with fewer quantization bits while maintaining robustness against transmission channel errors.
What features set this work apart from similar achievements?
It is possible to transmit prediction coefficients directly. Quantizing predictive coefficients, however, needs many bits for maintaining the LPC spectral shape. It is also difficult to avoid the risk of instability of the coding system. Partial auto correlation (PARCOR), invented by Dr. F. Itakura and Dr. S. Saito in 1972, enables an easy stability check but still needs many bits of quantization to maintain the LPC spectral shape. It is possible to reduce bit consumption for quantizing PARCOR by applying adaptive bit allocation and variable length coding schemes. Both schemes are, however, extremely sensitive to transmission channel errors. LSP, an alternative representation technology for prediction coefficients, was invented by Dr. F. Itakura in 1975 . It enables a simple stability check and can maintain the LPC spectrum shape with around 30% less bit consumption than PARCOR, even without using adaptive bit allocation or the variable length coding schemes  – . This is because the quantization distortion of LSP has smaller and more natural influences on LPC spectral shape than PARCOR. Thus, small LPC spectral distortion is achieved by efficient coding of LSP in combination with prediction, interpolation, and vector quantization.
References to establish the dates, location, and importance of the achievement:
 B. S. Atal, “The History of Linear Prediction”, IEEE SIGNAL PROCESSING MAGAZINE, pp. 154-157, MARCH 2006.
 F. Itakura, “Line Spectrum Representation of Linear Predictive Coefficients of Speech Signals,” J. Acoust. Soc. Am., 57, 533(A), 1975.
 JP Patent 56051116 - ALL POLE TYPE DIGITAL FILTER invented by F. Itakura http://worldwide.espacenet.com/publicationDetails/biblio?DB=EPODOC&II=8&ND=6&adjacent=true&locale=en_EP&FT=D&date=19810508&CC=JP&NR=56051116A&KC=A
 US Patent 4,393,272 Sound synthesizer invented by F. Itakura and N. Sugamura http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=4,393,272.PN.&OS=PN/4,393,272&RS=PN/4,393,272
 F. Itakura, “Statistical Methods for Speech Analysis and Synthesis –from ML Vocoder to LSP through PARCOR –,” IEICE Fundamental Review Vol.3 No.3. 2010. (in Japanese) Abstract: The invention process of the line spectrum air (LSP), one of the most important analysis technologies for speech signals, is described. Partial auto correlation (PARCOR) and LSP are alternative representation methods for a speech spectrum shape or a vocal tract shape. Both methods were invented at NTT Labs in 1972 and 1975, respectively. This paper covers the processes for these inventions, starting from the original invention of a speech analysis method based on maximum likelihood estimation in 1966.
 F. Itakura, T. Kobayashi and M. Honda, “A Hardware implementation of a new narrow and medium band speech coding,”, Proc. ICASSP 82, pp. 1964 – 1967, 1982.
 F. Soong and B. H. Juan, “Line spectrum pair (LSP) and speech data compression,” Proc. ICASSP 84, Vol. 9, pp. 37 – 40, 1984.
Supporting materials (supported formats: GIF, JPEG, PNG, PDF, DOC):
 ITU-T G.723.1(Dual rate speech coder for multimedia communications transmitting at 5.3 and 6.3 kbit/s) http://www.itu.int/rec/T-REC-G.723.1-200605-I,section 2.4-2.7
 ITU-T G.729(Coding of speech at 8 kbit/s using conjugate structure algebraic-code-excited linear prediction (CS-ACELP)) http://www.itu.int/rec/T-REC-G.729-200701-S, section 3.2
 3GPP AMRhttp://www.etsi.org/deliver/etsi_ts/126000_126099/126090/10.01.00_60/ts_126090v100100p.pdf, section 5.2
 3GPP2 EVRC http://www.3gpp2.org/public_html/specs/C.S0014-0_v1.0_revised.pdf, section 4.2
 IETF SILKhttp://tools.ietf.org/html/draft-vos-silk-01, page 261
 Example of VoIP gateway supporting G. 729 http://www.cisco.com/en/US/docs/ios/solutions_docs/voip_solutions/CAC.html