Editing Speech coding (section)

{{Short description|Lossy audio compression applied to human speech}}
{{Use American English|date=May 2022}}
{{more citations needed|date=January 2013}}

'''Speech coding''' is an application of [[data compression]] to [[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 data compression algorithms to represent the resulting modeled parameters in a compact bitstream.<ref>{{cite journal|first1=M. |last1=Arjona Ramírez|first2=M.|last2=Minam|title=Low bit rate speech coding|journal=Wiley Encyclopedia of Telecommunications, J. G. Proakis, Ed.|location=New York| publisher=Wiley|year=2003| volume= 3|pages=1299–1308}}</ref>

Common applications of speech coding are [[mobile telephony]] and [[voice over IP]] (VoIP).<ref>M. Arjona Ramírez and M. Minami, "Technology and standards for low-bit-rate vocoding methods," in The Handbook of Computer Networks, H. Bidgoli, Ed., New York: Wiley, 2011, vol. 2, pp. 447–467.</ref> The most widely used speech coding technique in mobile telephony is [[linear predictive coding]] (LPC), while the most widely used in VoIP applications are the LPC and [[modified discrete cosine transform]] (MDCT) techniques.{{Citation needed|date=December 2019}}

The techniques employed in speech coding are similar to those used in [[audio data compression]] and [[audio coding]] where appreciation of [[psychoacoustics]] is used to transmit only data that is relevant to the human auditory system. For example, in [[voiceband]] speech coding, only information in the frequency band 400 to 3500&nbsp;Hz is transmitted but the reconstructed signal retains adequate [[Intelligibility (communication)|intelligibility]].

Speech coding differs from other forms of audio coding in that speech is a simpler signal than other audio signals, and statistical information is available about the properties of speech. As a result, some auditory information that is relevant in general audio coding can be unnecessary in the speech coding context. Speech coding stresses the preservation of intelligibility and ''pleasantness'' of speech while using a constrained amount of transmitted data.<ref>P. Kroon, "Evaluation of speech coders," in Speech Coding and Synthesis, W. Bastiaan Kleijn and K. K. Paliwal, Ed., Amsterdam: Elsevier Science, 1995, pp. 467-494.</ref> In addition, most speech applications require low coding delay, as [[Latency (audio)|latency]] interferes with speech interaction.<ref>J. H. Chen, R. V. Cox, Y.-C. Lin, N. S. Jayant, and  M. J. Melchner, A low-delay CELP coder for the CCITT 16 kb/s speech coding standard. IEEE J. Select. Areas Commun. 10(5): 830-849, June 1992.</ref>