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 data compression algorithms to represent the resulting modeled parameters in a compact bitstream; some applications of speech coding are mobile telephony and voice over IP. The most used speech coding technique in mobile telephony is linear predictive coding, while the most used in VoIP applications are the LPC and modified discrete cosine transform techniques; the techniques employed in speech coding are similar to those used in audio data compression and audio coding where knowledge in psychoacoustics is used to transmit only data, relevant to the human auditory system. For example, in voiceband speech coding, only information in the frequency band 400 Hz to 3500 Hz is transmitted but the reconstructed signal is still adequate for intelligibility. Speech coding differs from other forms of audio coding in that speech is a simpler signal than most other audio signals, a lot more statistical information is available about the properties of speech.
As a result, some auditory information, relevant in audio coding can be unnecessary in the speech coding context. In speech coding, the most important criterion is preservation of intelligibility and "pleasantness" of speech, with a constrained amount of transmitted data. In addition, most speech applications require low coding delay, as long coding delays interfere with speech interaction. Speech coders are of two types: Waveform coders Time-domain: PCM, ADPCM Frequency-domain: sub-band coding, ATRAC Vocoders Linear predictive coding Formant coding From this point of view, the A-law and μ-law algorithms used in traditional PCM digital telephony can be seen as an earlier precursor of speech encoding, requiring only 8 bits per sample but giving 12 bits of resolution; the logarithmic companding laws are consistent with human hearing perception in that a low-amplitude noise is heard along a low-amplitude speech signal but is masked by a high-amplitude one. Although this would generate unacceptable distortion in a music signal, the peaky nature of speech waveforms, combined with the simple frequency structure of speech as a periodic waveform having a single fundamental frequency with occasional added noise bursts, make these simple instantaneous compression algorithms acceptable for speech.
A wide variety of other algorithms were tried at the time on delta modulation variants, but after a careful consideration, the A-law/μ-law algorithms were chosen by the designers of the early digital telephony systems. At the time of their design, their 33% bandwidth reduction for a low complexity made an excellent engineering compromise, their audio performance remains acceptable, there was no need to replace them in the stationary phone network. In 2008, G.711.1 codec, which has a scalable structure, was standardized by ITU-T. The input sampling rate is 16 kHz. Much of the works in speech compression was motivated by military research into digital communications for secure military radios, where low data rates were required to allow effective operation in a hostile radio environment. At the same time, far more processing power was available, in the form of VLSI circuits, than was available for earlier compression techniques; as a result, modern speech compression algorithms could use far more complex techniques than were available in the 1960s to achieve far higher compression ratios.
These techniques were available through the open research literature to be used for civilian applications, allowing the creation of digital mobile phone networks with higher channel capacities than the analog systems that preceded them. The most used speech coding algorithms are based on linear predictive coding. In particular, the most common speech coding scheme is the LPC-based Code Excited Linear Prediction coding, used for example in the GSM standard. In CELP, the modelling is divided in two stages, a linear predictive stage that models the spectral envelope and code-book based model of the residual of the linear predictive model. In CELP, linear prediction coefficients are computed and quantized as line spectral pairs. In addition to the actual speech coding of the signal, it is necessary to use channel coding for transmission, to avoid losses due to transmission errors. Speech coding and channel coding methods have to be chosen in pairs, with the more important bits in the speech data stream protected by more robust channel coding, in order to get the best overall coding results.
The modified discrete cosine transform, a type of discrete cosine transform algorithm, was adapted into a speech coding algorithm called LD-MDCT, used for the AAC-LD format introduced in 1999. MDCT has since been adopted in voice-over-IP applications, such as the G.729.1 wideband audio codec introduced in 2006, Apple's Facetime introduced in 2010, the CELT codec introduced in 2011. Opus is a free software speech coder, it combines both the MDCT and LPC audio compression algorithms. It is used for VoIP calls in WhatsApp; the PlayStation 4 video game console uses the CELT/Opus codec for its PlayStation Network system party chat. Codec2 is another free software speech coder, which manages to achieve good compression, as low as 700 bit/s. Wideband audio codingLinear predictive coding AMR-WB for WCDMA networks VMR-WB for CDMA2000 networks Speex, IP-MR, SILK and Opus for voice-over-IP and videoconferencing Modified discrete cosine transform AAC-LD, G.722.1, G.729.1, CELT and Opus for VoIP and video
Sunny Skylar was an American composer, singer and music publisher. He was born Selig Shaftel in New York; as a singer, he appeared with a number of big bands, including those led by Ben Bernie, Paul Whiteman, Abe Lyman, George Hall and Vincent Lopez. It was Lopez. After the end of the big band era, Skylar continued to sing in nightclubs and theaters until 1952. Among the songs he wrote are: "Amor" "And So to Sleep Again" "Atlanta, G. A." "Bésame Mucho" "Cry, Cry" "Don't Wait Too Long" "Gotta Be This or That" "Hair of Gold, Eyes of Blue" "I Miss Your Kiss" "It Must Be Jelly" "Louisville, K. Y." "Love Me with All Your Heart" "Where There's Smoke, There's Fire" "You're Breaking My Heart" "If You Loved Me"
Liu Jiang is a Chinese retired politician who served as minister of Agriculture of the People's Republic of China between 1993 and 1998. Liu was a member of the 15th CPC Central Committee and 16th Committee of the Central Commission for Discipline Inspection, he was a member of the 10th National Committee of the Chinese People's Political Consultative Conference and a member of the 11th Standing Committee of the Chinese People's Political Consultative Conference. Liu was born in Beijing in April 1940. In December 1964 he graduated from the College of Agriculture in Xinjiang Production and Construction Corps, where he majored in animal husbandry. After gradation, he was assigned to Tibet Military District, where he worked until August 1972. In August 1972, Liu became a technician at Beijing Municipal Animal Husbandry and Veterinary Station, five years he was promoted to become its deputy director. Liu was the head of Beijing Red Star Chicken Farm in December 1979, held that office until July 1982.
In 1982 he was promoted to become director of the Bureau of Animal Industry in Beijing, a position he held until 1986. In January 1986, he was appointed vice-minister of Agriculture of the People's Republic of China, he remained in that position until November 1990, when he appointed deputy director of the State Planning Commission, he rose to become minister of Agriculture of the People's Republic of China in March 1993, served until March 1998. He served as deputy director the National Development and Reform Commission from March 1998 to March 2003, again from March 2003 to August 2005. In February 2005 he was appointed deputy director of the Committee for Ethnic and Religious Affairs, an institution under the jurisdiction of the Chinese People's Political Consultative Conference