Edit Proposal: Milestone-Proposal:Line spectrum pair (LSP), an essential technology for high-compression speech coding, 1975

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Line Spectrum Pair, invented at NTT in 1975, is an important technology for speech synthesis and coding. A speech synthesizer chip was designed based on Line Spectrum Pair in 1980. In the 1990s, this technology was adopted in almost all international speech coding standards as an essential component and has contributed to the enhancement of digital speech communication over mobile channels and the Internet worldwide.

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• the historic significance of the achievement,
• its importance to the evolution of electrical and computer engineering and science,
• its importance to regional/national/international development,
• its benefits to humanity,
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improvement of existing technology.

The material submitted here will constitute the main descriptive article on the ETHW website for readers to learn about the milestone. Space is unlimited, and detail is encouraged. Most milestones require 1000 to 1500 words of support, however there is no word limit. The article should be readable by a wide audience that includes practicing engineers, scholars of history, and the general public. Some examples of the text of good milestone articles are First Radio Astronomical Observations Using Very Long Baseline Interferometry] and G3_Facsimile International Standardization of G3 Facsimile (Do not worry about the formatting of the page, IEEE History Center Staff will do that afterwards.)

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 [1]. 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 [2]. 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 [3] – [7]. 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.

Supporting texts and citations to establish the dates, location, and importance of the achievement. You must supply the texts or excerpts themselves, not just the references. Minimum of five (5), but as many as needed to support the milestone, such as patents, contemporary newspaper articles, journal articles, or chapters in scholarly books. At least one of the references must be from a scholarly book or journal article. 'Scholarly' is defined as peer-reviewed, with references, and published. The full reference, in English, must be uploaded, not just the citation. See below section for details on uploading material to the website. All supporting materials must be in English, or accompanied by an English translation.

[1] B. S. Atal, “The History of Linear Prediction”, IEEE SIGNAL PROCESSING MAGAZINE, pp. 154-157, MARCH 2006. [2] F. Itakura, “Line Spectrum Representation of Linear Predictive Coefficients of Speech Signals,” J. Acoust. Soc. Am., 57, 533(A), 1975. [3] 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 [4] 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 [5] 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. [6] 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. [7] 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) which can be made publicly available on the IEEE History Center’s website (i.e. unencumbered by copyright, or with the copyright holder’s permission). All supporting materials must be in English, or if not in English, accompanied by an English translation. You must supply the texts or excerpts themselves, not just the references. Images and photographs are especially appreciated, however, it is necessary that you list the copyright owner for these and obtain the copyright owner’s permission to reuse. For documents that are copyright-encumbered, or which you do not have rights to post, email the documents themselves to ieee-history@ieee.org. Please see the Milestone Program Guidelines for more information.

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[8] 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 [9] 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 [10] 3GPP AMRhttp://www.etsi.org/deliver/etsi_ts/126000_126099/126090/10.01.00_60/ts_126090v100100p.pdf, section 5.2 [11] 3GPP2 EVRC http://www.3gpp2.org/public_html/specs/C.S0014-0_v1.0_revised.pdf, section 4.2 [12] IETF SILKhttp://tools.ietf.org/html/draft-vos-silk-01, page 261 [13] Example of VoIP gateway supporting G. 729 http://www.cisco.com/en/US/docs/ios/solutions_docs/voip_solutions/CAC.html

Please email a jpeg or PDF a letter in English, or with English translation, from the site owner(s) giving permission to place IEEE milestone plaque on the property, and a letter (or forwarded email) from the appropriate Section Chair supporting the Milestone application to ieee-history@ieee.org with the subject line "Attention: Milestone Administrator." Note that there are multiple texts of the letter depending on whether an IEEE organizational unit other than the section will be paying for the plaque(s).

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