20th Century Music Audio Timeline

Overture

Initially, I just wanted to understand all the different branches of rock music out there today and how they relate to each other, but that naturally evolved into researching how all the different branches of popular music evolved throughout the 20th century. There are a lot of sources on the web that have annoyingly incomplete fragments of the whole story, and none that I could find that included clips of the actual music being discussed, so that's mostly what this article will do: attempt to give a 500-ft view of all the different kinds of popular music out there today, complete with audio examples.

Disclaimers:

• I am not a subject matter expert and most of the information here is probably going to be blatantly lifted from Wikipedia and other crowd-sourced sources. I'm also going to be talking about music theory, a subject on which I have minimal exposure and no formal training, so the information may be off or just blatantly wrong on multiple levels.
• I don't really care about the evolution of certain genres of music (like country), so this will not be comprehensive or exhaustive. I'll talk about them if there is something interesting to be said.
• I have to use examples to illustrate some of these points, and that means I have to pick one or two bands to exemplify a particular sound or movement. I'm really sorry if I happened to not pick your favorite band. I wasn't born when a lot of these people were famous and I do not count myself as familiar with most popular music scenes so I apologize in advance if I offend anyone here with my choice of examples.
• I'm going to try really hard not to insert my personal opinion of the state of popular music today, but there will be times when good taste will triumph over restraint.
  
• This is mostly an attempt to gain some perspective on how pop music evolved, so that when someone makes a statement like "The Vienna Franks are a good example of urban white acid folk revivalism laced with ska," I will have a better foundation to understand just how ridiculous of a statement that is. I make no attempts to be rigorous or scholarly.

The Colour and the Shape

Broad Trends, Musical Formats
Classical Music up to 1950s or so: Mahler, Gershwin, Debussy, Ravel, Copland, Prokofiev, John Cage
Jazz up to 1950s or so: Ragtime, Big Band/Swing, Bebop, Cool Jazz
1950s: Rock and Roll is born: Elvis Presley, Buddy Holly, Bill Haley, Richie Valens. "Rockabilly" is born. Blues is popularized by Ray Charles and Fats Domino, who introduced "boogie-woogie."
1960s: Bubblegum pop: the Monkees, folk music, Bob Dylan, the Beatles and the British Invasion (The Who), San Francisco sound: The Grateful Dead and Jefferson Airplane and the birth of psychedelic rock (Hendrix and the Doors), progressive rock. Soul and Motown develop. Johnny Cash and Dolly Parton. Woodstock. Vietnam.
1970s: Lots of Famous People Die. Glam rock (David Bowie). German-inspired kraut-rock influences prog-rock (Jethro Tull, Pink Floyd), punk (Ramones, Sex Pistols, the Clash) and New Wave (Talking Heads). Hard Rock develops with Led Zeppelin, Black Sabbath. Country rock (the Eagles). Metal starts up (AC/DC, Aerosmith, Def Leppard). It is the age of disco (Bee Gees). Funk (James Brown) is also popular. Bob Marley and reggae become popular. 1979 saw the birth of hip-hop music with the song Rapper's Delight by Sugarhill Gang. Improvements in cassette tape technology makes it competitive to the 12-inch vinyl LP gramaphone.
1980s: alternative rock (U2 and REM). New Wave: new Romantic (David Bowie) and CBGB-style punk. Arena rock: Journey. Glam Metal/hair metal: Van Halen, Queen, Kiss. Hard rock/metal: Motley Crue, Iron Maiden, Metallica, Guns 'n Roses, Aerosmith. Orchestra-heavy disco is replacced by lighter synthpop. Teenpop is born: Madonna and Whitney Houston are popular. Michael Jackson releases Thriller in 1982. Hip hop: Run DMC, Salt n Peppa, Grandmaster Flash.
1990s: Teen pop singers and boy bands (Britney Spears, Backstreet Boys, Spice Girls). R&B: (Usher, R Kelly, Aaliyah). Alternative rock continues (Our Lady Peace, Red Hot Chili Peppers, Smashing Pumpkins), Grunge (Nirvana, Pearl Jam, Alice in Chains, Soundgarden). Pop punk (Greenday, Third Eye Blind). Britpop (Oasis, Blur). Indie Rock (the Pixies, Flaming Lips), Third Wave Ska (Mighty Mighty Bosstones). Hip hop explodes: Puff Daddy, Dr. Dre, 2Pac. Singer-songwriter revival (Alanis Morisette, Tori Amos). Industrial music spawns industrial metal (Nine Inch Nails). Other electronic movements such as house and techno music lead to trance. Massive Attack spawns the trip hop movement. European death metal (Rammstein).
2000s: The Hip Hop trend continues and surpasses rock as the dominant musical form: crunk and gangsta rap. Alternative rock spawns post grunge (Creed, Nickleback, Foo Fighters), numetal (Linkin Park, Evanescence), and emo (Dashboard Confessional, My Chemical Romance). Metal is popular again (Slayer), and death metal is popular in Europe. British invasion (Coldplay, Radiohead, Muse). Pop punk continues (Fall Out Boy). Indie Rock becomes very popular (the Strokes), more commercialized (Modest Mouse, Death Cab for Cutie), and becomes catch-all term for non-commercial bands, also spawning lots of odd categories (chamber pop/baroque pop) because indie rock doesn't have a unified sound. Electropop remains big: Christina Aguilera, Lady Gaga. R&B/Hip Hop is still huge. Ethnic music (is a terrible category name): Shakira, MIA. Country music is big. K-pop and J-pop are huge in Japan.

On with the Show

Technology changed the face of popular music on a lot of fronts. New instruments such as the synthesizer, the drum machine, the electric guitar, and the theremin were invented, which created genres built around new sounds. The radio and the rise of popular recording formats made music easier to distribute; musicians could now reach a wider audience than ever before. Music became more portable; we can now take our own music with us in CD players or iPods and listen to our own collection on headphones. Musicians can travel all over the world with ease and play to huge audiences with the rise of amplification techniques in stadium concerts. The music video as a form of popular dissemination rose to fame. The advent of digital music and file sharing is still changing the face of musical distribution in ways that the recording industry hasn't really caught onto yet.

The vinyl disc emerged as the first true hi-fi format around the 1930s and still holds some sway as the format of choice amongst really hard-core audiophiles. Around 1963 the cassette tape came into play, but it didn't really hit its stride until the advent of the Sony Walkman in the 1980s. There was a period of time in the 60s when the 8-track tape was popular, but it seems to be mostly a dead format now. I've never even seen one. In the 1980s, the CD emerged and still remains a popular format, even though the sound quality cannot compare with true analog. In the 90s, the MP3, the first truly digital format to receive any kind of wide acceptance, rose to prominence; however, as it is a lossy format, it will never have the same kind of audio quality as a CD, even though most people can't really tell the difference anyway. Then we get into the era of iTunes DRM and other ugly proprietary formats, a fight which the music industry is doomed to lose to common sense. There are also two audiophile versions of the CD, which are SACD and DVD Audio, although neither of them have gained much popularity since most people don't even have the equipment needed to play them.