music fell in two categories: guitar, drum and bass groups or singers backed by a traditional orchestra. Since early in the decade, it was common for pop producers, songwriters, and engineers to freely experiment with musical form, orchestration, unnatural reverb, and other sound effects. Some of the best known examples are Phil Spector's Wall of Sound and Joe Meek's use of homemade electronic sound effects for acts like the Tornados. At the same time, pop music on radio and in both American and British film moved away from refined Tin Pan Alley to more eccentric songwriting and incorporated reverb-drenched rock guitar, symphonic strings, and horns played by groups of properly arranged and rehearsed studio musicians. A 2019 study held by New York University in which 643 participants had to rank how familiar a pop song is to them, songs from the 1960s turned out to be the most memorable, significantly more than songs from recent years 2000 to 2015. Before the progressive pop of the late 1960s, performers were typically unable to decide on the artistic content of their music. Assisted by the mid-1960s economic boom, record labels began investing in artists, giving them the freedom to experiment, and offering them limited control over their content and marketing. This situation declined after the late 1970s and would not reemerge until the rise of Internet stars. Indie pop, which developed in the late 1970s, marked another departure from the glamour of contemporary pop music, with guitar bands formed on the then-novel premise that one could record and release their own music without having to procure a record contract from a major label. The 1980s are commonly remembered for an increase in the use of digital recording, associated with the usage of synthesizers, with synth-pop music and other electronic genres featuring non-traditional instruments increasing in popularity. By 2014, pop music worldwide had been permeated by electronic dance music. In 2018, researchers at the University of California, Irvine, concluded that pop music has become 'sadder' since the 1980s. The elements of happiness and brightness have eventually been replaced with electronic beats making pop music more 'sad yet danceable'. International spread and crosspollination Pop music has been dominated by the American and (from the mid-1960s) British music industries, whose influence has made pop music something of an international monoculture, but most regions and countries have their own form of pop music, sometimes producing local