<P> The theme and incidental music were composed by David Arnold and Michael Price . Arnold explains that he and Price worked with the producers to "come up with a central theme and character" for the series, then found what was "going to be the defining sound of this show". Pieces were often constructed using synthesizers, but the tracks used for the show were recorded using real musicians, Arnold says, to bring the music "to life". Similarly, Price comments that the musicians can adapt their performance of a score by responding to footage from the show . </P> <P> Four series, each consisting of three episodes, have been produced . The first series was initially broadcast in July and August 2010 on the BBC, later premiering on Public Broadcasting Service (PBS) in the United States in October 2010 . A second series of three episodes was first broadcast in the UK in January 2012, and then in the U.S. during May 2012 . The third series premiered in the UK on 1 January 2014 and in the US on 19 January 2014 . The series has been sold to 180 territories . A special episode premiered on 1 January 2016, on BBC One and PBS, marking the first time the series has aired on the same day in the UK and U.S. The fourth series began airing on BBC One and PBS on 1 January 2017 and concluded on 15 January 2017 . </P> <Table> <Tr> <Th_colspan="2"> Series </Th> <Th_colspan="2"> Episodes </Th> <Th_colspan="2"> Originally aired </Th> <Th_colspan="2"> Average ratings (millions) </Th> </Tr> <Tr> <Th> First aired </Th> <Th> Last aired </Th> <Th> UK </Th> <Th> U.S. </Th> </Tr> <Tr> <Td> </Td> <Td_colspan="1"> </Td> <Td_colspan="2"> </Td> <Td_colspan="1"> 25 July 2010 (2010 - 07 - 25) </Td> <Td> 8 August 2010 (2010 - 08 - 08) </Td> <Td> 8.37 </Td> <Td> N / A </Td> </Tr> <Tr> <Td> </Td> <Td_colspan="1"> </Td> <Td_colspan="2"> </Td> <Td_colspan="1"> 1 January 2012 (2012 - 01 - 01) </Td> <Td> 15 January 2012 (2012 - 01 - 15) </Td> <Td> 10.23 </Td> <Td> 4.4 </Td> </Tr> <Tr> <Td> </Td> <Td_colspan="1"> </Td> <Td_colspan="2"> </Td> <Td_colspan="1"> 1 January 2014 (2014 - 01 - 01) </Td> <Td> 12 January 2014 (2014 - 01 - 12) </Td> <Td> 11.82 </Td> <Td> 6.6 </Td> </Tr> <Tr> <Td> </Td> <Td_colspan="3"> Special </Td> <Td_colspan="2"> 1 January 2016 (2016 - 01 - 01) </Td> <Td> 11.64 </Td> <Td> 3.4 </Td> </Tr> <Tr> <Td> </Td> <Td_colspan="1"> </Td> <Td_colspan="2"> </Td> <Td_colspan="1"> 1 January 2017 (2017 - 01 - 01) </Td> <Td> 15 January 2017 (2017 - 01 - 15) </Td> <Td> 10.00 </Td> <Td> N / A </Td> </Tr> </Table> <Tr> <Th_colspan="2"> Series </Th> <Th_colspan="2"> Episodes </Th> <Th_colspan="2"> Originally aired </Th> <Th_colspan="2"> Average ratings (millions) </Th> </Tr>

When did series 4 of sherlock come out