SUMMARY / RELATED TOPICS

Linear predictive coding

Linear predictive coding is a method used in audio signal processing and speech processing for representing the spectral envelope of a digital signal of speech in compressed form, using the information of a linear predictive model. It is one of the most powerful speech analysis techniques, one of the most useful methods for encoding good quality speech at a low bit rate and provides accurate estimates of speech parameters. LPC is the most used method in speech coding and speech synthesis. LPC starts with the assumption that a speech signal is produced by a buzzer at the end of a tube, with occasional added hissing and popping sounds. Although crude, this model is a close approximation of the reality of speech production; the glottis produces the buzz, characterized by its intensity and frequency. The vocal tract forms the tube, characterized by its resonances. Hisses and pops are generated by the action of the tongue and throat during sibilants and plosives. LPC analyzes the speech signal by estimating the formants, removing their effects from the speech signal, estimating the intensity and frequency of the remaining buzz.

The process of removing the formants is called inverse filtering, the remaining signal after the subtraction of the filtered modelled signal is called the residue. The numbers which describe the intensity and frequency of the buzz, the formants, the residue signal, can be stored or transmitted somewhere else. LPC synthesizes the speech signal by reversing the process: use the buzz parameters and the residue to create a source signal, use the formants to create a filter, run the source through the filter, resulting in speech; because speech signals vary with time, this process is done on short chunks of the speech signal, which are called frames. The origins of linear predictive coding date back to 1966, when the concept was first proposed by Fumitada Itakura of Nagoya University and Shuzo Saito of Nippon Telegraph and Telephone, they described an approach to automatic phoneme discrimination that involved the first maximum likelihood approach to speech coding. In 1967, John Burg outlined a maximum entropy approach.

In 1969, Itakura and Saito introduced partial correlation, Glen Culler proposed real-time speech encoding, Bishnu S. Atal presented an LPC speech coder at the Annual Meeting of the Acoustical Society of America. In 1971, realtime LPC using 16-bit LPC hardware was demonstrated by Philco-Ford. LPC is the basis for voice-over-IP technology. In 1972, Bob Kahn of ARPA, with Jim Forgie and Dave Walden, started the first developments in packetized speech, which would lead to voice-over-IP technology. In 1973, according to Lincoln Laboratory informal history, the first real-time 2400 bit/s LPC was implemented by Ed Hofstetter. In 1974, the first real-time two-way LPC packet speech communication was accomplished over the ARPANET at 3500 bit/s between Culler-Harrison and Lincoln Laboratory. In 1976, the first LPC conference took place over the ARPANET using the Network Voice Protocol, between Culler-Harrison, ISI, SRI, LL at 3500 bit/s. LPC technology was advanced by Manfred Schroeder during the 1970s -- 1980s.

In 1978, Atal and Vishwanath et al. of BBN developed the first variable-rate LPC algorithm. The same year and Manfred R. Schroeder at Bell Labs proposed an LPC speech codec called adaptive predictive coding, which used a psychoacoustic coding algorithm exploiting the masking properties of the human ear; this became the basis for the perceptual coding technique used by the MP3 audio compression format, introduced in 1993. Code-excited linear prediction was developed by Schroeder and Atal in 1985. LPC is used for transmitting spectral envelope information, as such it has to be tolerant of transmission errors. Transmission of the filter coefficients directly is undesirable, since they are sensitive to errors. In other words, a small error can distort the whole spectrum, or worse, a small error might make the prediction filter unstable. There are more advanced representations such as log area ratios, line spectral pairs decomposition and reflection coefficients. Of these LSP decomposition has gained popularity since it ensures the stability of the predictor, spectral errors are local for small coefficient deviations.

LPC is the most used method in speech coding and speech synthesis. It is used for speech analysis and resynthesis, it is used as a form of voice compression by phone companies, such as in the GSM standard, for example. It is used for secure wireless, where voice must be digitized and sent over a narrow voice channel. LPC synthesis can be used to construct vocoders where musical instruments are used as an excitation signal to the time-varying filter estimated from a singer's speech; this is somewhat popular in electronic music. Paul Lansky made the well-known computer music piece notjustmoreidlechatter using linear predictive coding. A 10th-order LPC was used in the popular 1980s Spell educational toy. LPC predictors are used in Shorten, MPEG-4 ALS, FLAC, SILK audio codec, other lossless audio codecs. LPC is receiving some attention as a tool for use in the tonal analysis of violins

Easy Rock Network

Easy Rock is an adult contemporary music radio brand of Manila Broadcasting Company. Its main studios are located in Pasay City, Metro Manila, its flagship station is DWRK in Metro Manila, with seven regional stations located throughout the Philippines either owned by MBC or its sister companies within the company's media group. The Easy Rock Network was formed on May 18, 2009; the formation of the Easy Rock Network started with an initial rebrand of the newly acquired DWRK radio station, which MBC bought from the ACWS-United Broadcasting Network on October 6, 2008. The Easy Rock network was expanded by rebranding a number of former Yes FM stations, Love Radio and Hot FM stations to Easy Rock; the format of Easy Rock resembles that of WRocK, with "no/minimal talk, less commercials and more music". But while most of the regional stations maintained its traditional format, the Manila station shifted to Mainstream AC with its playlist being more identical to that of sister stations Love Radio and Yes The Best.

Further information: Easy Rock stationsEasy Rock is broadcast to 11 provincial stations in the Philippines Manila Broadcasting Company

History of slavery in Missouri

The history of large-scale slavery in the State of Missouri began in 1720, when a French entrepreneur named Philippe François Renault brought about 500 negro slaves from Saint-Domingue up the Mississippi River to work in lead mines in what is now southeastern Missouri and southern Illinois. These people were the first enslaved Africans brought en masse to the middle Mississippi River Valley. Prior to Renault's enterprise, slavery in Missouri under French colonial rule had been practiced on a much smaller scale as compared to elsewhere in the French colonies; the institution of slavery only became prominent in the area following two major events: the invention of the cotton gin by Eli Whitney in 1793, the Louisiana Purchase in 1803. These events led to the westward migration of slave-owning settlers into the area of present-day Missouri and Arkansas known as Upper Louisiana; the majority of slave owners in Missouri had moved from worn-out agricultural lands in North Carolina, Tennessee and Virginia.

Still, cotton cultivation, arguably the industry to which slave labor was the most important, was never as well-suited to Missouri's climate as to the rest of the southern United States, was limited to the most southern parts of the state near the border with present-day Arkansas. Slavery in other areas of Missouri was concentrated in other agricultural industries, such as those for tobacco, hemp and livestock. A number of slaves was hired out as stevedores, cabin boys, or deck hands on the ferries of the Mississippi River. By the beginning of the American Civil War, only 36 counties in Missouri had 1,000 or more slaves. Male slaves fetched a price of up to $1,300. In the State Auditor's 1860 report, the total value of all slaves in Missouri was estimated at US$44,181,912. Missouri's territorial slave code was enacted in 1804, a year after the Louisiana Purchase, under which slaves were banned from the use of firearms, participation in unlawful assemblies, or selling alcoholic beverages to other slaves.

It severely punished slaves for participating in riots, insurrections, or disobedience of their masters. It provided for punishment by mutilation of a slave who sexually assaulted a white woman; the code was retained by the State Constitution of 1820. At the end of 1824, the Missouri General Assembly passed a law providing a process for enslaved persons to sue for freedom and have some protections in the process. An 1825 law passed by the General Assembly declared blacks incompetent as witnesses in legal cases which involved whites, testimonies by black witnesses were automatically invalidated. In 1847, an ordinance banning the education of blacks and mulattoes was enacted. Anyone caught teaching a black or mulatto person, whether enslaved or free, was to be fined $500 and serve six months in jail. Elijah Lovejoy edited an abolitionist newspaper, the Observer, in St. Louis before being driven out by a mob in 1836, he fled across the Mississippi River to Alton, where he was killed in an exchange of gunfire with a pro-slavery mob.

In 1846, one of the nation's most public legal controversies regarding slavery began in St. Louis Circuit Court. Dred Scott, a slave from birth, sued his owner's widow on the basis of a Missouri precedent that held that slaves freed through prolonged residence in a free state or territory would remain free upon returning to Missouri. Scott had spent several years living in Illinois and the Wisconsin Territory with his owner, Dr. John Emerson, before returning to Missouri in 1840. After Emerson's death, Emerson's widow refused to buy Scott's and his family's freedom, so Scott resorted to the legal action permitted him under Missouri's 1824 law. Scott lost his case in the Missouri Supreme Court, but brought legal suit again in 1853 under federal law; the case was appealed to the United States Supreme Court and became a flashpoint in the ongoing national debate over the legality of slavery. In 1857, the Supreme Court handed down its verdict in Dred Scott v. Sandford: slaves were not citizens, therefore Scott did not have the right to sue for his family's freedom.

The landmark decision found the provisions of the Missouri Compromise of 1820 unconstitutional, helped to fan the flames of conflict between pro-slavery and anti-slavery factions in the United States. The Scott family was granted freedom by their owners, but Scott died shortly after, in 1858; as one of the border states during the American Civil War, Missouri was exempt from President Abraham Lincoln's 1863 Emancipation Proclamation decreeing the freedom of slaves in all territory held by Confederate forces. On January 11, 1865, a state convention approved an ordinance abolishing slavery in Missouri by a vote of 60-4, the same day, Governor Thomas C. Fletcher followed up with his own "Proclamation of Freedom"; this action marked the end of legal slavery in the state of Missouri. Marguerite Scypion, a slave of African and Native American descent who sued for her freedom Missouri Constitutional Convention of 1861-1863 Slavery in Missouri Another history of slavery in Missouri