Read this: West's fourth studio album, 808s & Heartbreak (2008), marked an even more radical departure from his previous releases, largely abandoning rap and hip hop stylings in favor of a stark electropop sound composed of virtual synthesis, the Roland TR-808 drum machine, and explicitly auto-tuned vocal tracks. Drawing inspiration from artists such as Gary Numan, TJ Swan and Boy George, and maintaining a "minimal but functional" approach towards the album's studio production, West explored the electronic feel produced by Auto-Tune and utilized the sounds created by the 808, manipulating its pitch to produce a distorted, electronic sound; he then sought to juxtapose mechanical sounds with the traditional sounds of taiko drums and choir monks. The album's music features austere production and elements such as dense drums, lengthy strings, droning synthesizers, and somber piano, and drew comparisons to the work of 1980s post-punk and new wave groups, with West himself later confessing an affinity with British post-punk group Joy Division. Rolling Stone journalist Matthew Trammell asserted that the record was ahead of its time and wrote in a 2012 article, "Now that popular music has finally caught up to it, 808s & Heartbreak has revealed itself to be Kanye’s most vulnerable work, and perhaps his most brilliant."
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): What types of instruments are present on his fourth album?
dense drums, lengthy strings, droning synthesizers, and somber piano