Now this is a really, really interesting and provoking topic. Too bad it turned into a flamewar for a while, but as several people have stated, mbhaub's post showed real ignorance and lack of understanding about metal, and was sure to provoke an adverse reaction. Fortunately we are back on topic again. I personally do think that I have knowledge of both classical and metal music, just like a lot of other frequent darkest desires posters and other metal listeners on this forum do, so I try to avoid making any broad generalizations of either musical style. I even did study musicology for a few years (exploiting finnish free academic education is a bliss...).
I wouldn't say that there is a ongoing trend of classical musicians turning into metal. There are some, but I think it's more about metal bands implementing elements from western classical music and showing some will to merge with the classical music institution. In example, we have had metal operas in Finland. "Evankeliumi" was even performed in the finnish opera house. Swedish Entombed performed with ballet dancers and symphonic orchestras are often hired to play on metal albums. Of course there are also cases like Apocalyptica, where four professional cello players formed up a metal band and Tarja Turunen, who was originally a classical vocalists and ended up in a metal band. The list goes on...
Still, I think the more interesting topic is "What do metal and classical music have musically in common?". First of all, both are limited only by their instrumentation and musical institutions (or possibly art worlds). Looking at the history of western classical music, the only thing that hasn't completely changed during the times is the instrumentation, and in some cases, composers/musicians, who are connected to the classical music "scene", can also make wide sonical experimentations, like electroacoustic music from Stockhausen, Varese, Saariaho etc, and it's still considered as part of the classical music canon. Same goes for metal. It's main element has been distorted guitars, electric bass and loud drums, but the compositions and subgenres/styles have varied ernomously. Interestingly the evolution of metal music is somewhat similar to western classical music. Oldschool heavy metal (or new wave of british heavy metal) has a lot in common with baroque-era classical music. Less emphasize on harmony, more on virtuosic playing, contrasts and kind of contrapunctal composing, where we have simplified notes/chord progressions as rhytm and more expressive and lively melodies on top of them. Usually made up from a lot of short duration notes. This is most apparent in neo-classical metal. After that, a lot of metal bands started to slow down the tempo a bit (except extreme metal bands of course) and create a bit softer, more melodic approach. Just like composers of Wien-classical era did. Then we have nordic metal, which relied more on expressing (often dark) emotions than instrumental virtuosity. Nationality and cultural heritage also became frequent themes. This reminds me a lot of romantic and post-romantic era classical music. Finally we have avant-garde metal, technical metal, math-metal etc, which are musically really atonal, unharmonic, rhytmically complex and hard to listen. Some of the most complex tracks from Meshuggah differ from the works from ie. Schöenberg only by their instrumentation. Both classical and metal music in their extremes have moved further and further into composing soundscapes instead of notes. The modern atonal classical/electroacoustic music composer, Xenakis, even stated that the future of music is in composing sound, not notes.
There are even cases, where metal and classical music get so close to each other that it's hard to even categorize the music in either genre. This most often happens when metal bands abandon the metal instrumentation, and express their music with acoustic instruments. In musicology I did a short essay about Elend and why it's considered metal. I started the presentation by playing the track "La Terre N'Aime Pas Le Sang" (a very intense and chaotic piece played entirely by classical instruments) and asked the listeners, who mostly had experience only on classical music, if they could recognize the composer. Many of them thought it was a work of some composer of modern atonal art music. None of them had any idea that the track came from a band which is considered as part of the metal scene.
The idea of instrumentation being the only defining factor of a genre and musical freedom being more important than pleasing the wide audience also works for jazz and electronic music. In some cases even folk music. So why is metal closest to classical? Maybe because in a way, emotion has not been that imporant in pure electronic music, and compositions are not that complex or ambitious in jazz, which relies more on pure improvisation. Folk often favours simplicity, which may turn some classical musicians off.
Just my ideas. Feel free to comment.
