yupz... it's a very general question. But being a simple question as it is, i believe it is actually one of the hardest question to answer in song making especially production. Maybe i can be more specific.. From producing many songs, i have realise that some songs, as simple as they may seem when they were in their raw stages, actually turned out to be pretty complex during the stage of production. Either they end up with complex drum groove and variation, or they may have complex piano or organ riffs. Yet, there turn out to be some songs which are as simple as they look or turn out simple when though to be complex at the start.
These complexity actually makes the song's 'feel' better as compared when they are made simple. As for simple songs, complexities just don't work for them. Complex natures also can revolve in terms of arrangement. There were some songs i did in the past which i thought would have a simple arrangement (maybe i was just being lazy, who doesn't want an easier job!). But somehow, after listening back and forth, these songs actually had to have a more complex arrangement in order to bring out their emotions.
The simple answer would be the song's nature or character that brings forth whether they are meant to be complex or simple. Apparently, as musicians, simplicity seems the easier solution, but when we face the song as it is, understand it's character and nature, sometimes we have to face the fact when the song just had to have something (groove, melody, synths or arrangement!) complex.
There were songs that took me a shorter time to complete, everything came out more or less as it is, with only slight variations later, but somehow, simple as it is, nothing could be changed there after. But some songs have to be really dug in and out, even with my band, with major variations coming in and out over time, to get them right.
I believe it is not just me as a producer that faced this, even with bands coming out songs, i believe they do face songs that are more difficult than others.
I'm just wondering if there are any character or nature similarities between songs that are complex and those that are simple. Are there common traits between simple songs?? Are there common traits between complex ones?? I'm still digging this question, maybe you can give me your opinions.