What do you think - can listening to songs in German be helpful when learning the language? Can it improve listening comprehension and understanding of speech?
The lyrics in classical music are often stilted, frequently concerning religious topics and in modern popular music they are often full of puns, revolving around romantic topics. Also, rhyme and rhythm are usually more important than pronunciation and grammar, which could make the language better resemble the one actually spoken than in most other written texts (incl. theater and film), but often it doesn’t.
I’m a native speaker of German and on proficiency level C2 for reading and listening comprehension of English, but as soon as it’s sung (even rapped) my understanding plummets in both languages unless I intentionally try to concentrate on the words. I may be able to hum the melody and perhaps can recite the chorus, but have not the least of an idea what a song was all about. I don’t think I’m alone with that.
Therefore, I would suggest listening to songs as a learning device only to those beginners and intermediates for whom music and poetry provide an inherent motivation to learn the language in the first place. If, as an advanced learner, you really want to understand a language and the culture associated with it, you will need to know some of its musical canon. This doesn’t mean you’d need to know or understand the lyrics to Ode an die Freude, for instance, because that’s more of a melodic heritage than a textual one, but it won’t hurt (your language proficiency) to get to know some of the modern classic. There are popular compilations like Fetenhits to get you started.
Crissov's answer is a very good one, but I will give a contrary answer based on my own language learning experience. Your mileage may vary.
I learned both German and Japanese to a high degree of fluency as an adult, and memorizing poetry and song lyrics was a major part of my process in both languages. It's important not to just start memorizing whatever you hear on the radio, though. You want music that is interesting to you (so that you'll be motivated to learn it), but also that is written in grammatically correct German, ideally in complete sentences, and not sung in a strong dialect.
A good example of a German artist that I found helpful is Reinhard Mey. He's a singer-songwriter with beautiful, grammatically correct lyrics that don't contain a great deal of slang, and his pronunciation is very clear Hochdeutsch. I can also recommend the Wise Guys, an acapella group from Köln, that also have a lot of songs I found to be good practice.
Have at it, but choose carefully. My high school German teacher brought beer hall songs in December instead of christmas carols. That was in 1982-84 and I can still remember most of them (unfortunately he didn't bring German beer too). We also knew the full lyrics (and meaning) of Nena's 99 Luftballons, a huge hit at the time.
Nena also has a lovely voice, and you can repeat anything you learn there in polite company. Better to remember "singe ich ein Lied für dich" than "Horst Wessel Lied" when you want "song".
Rammstein would be a rather poor choice here, unless you plan on going to some of the unmarked basement bars near the Reeperbahn and can handle yourself in a fight.