Adorno and Horkeimer are both philosophers from Frankfurt school who are most know for their work on the Culture Industry and their book "Dialectic of Enlightenment" which is also mostly about the cultural industry.
Within there book Adorno and Horkeimer argue that the culture industry exhibits an "assembly-live character which could be observed in the synthetic". What this basically means is that the culture is made through the culture industry and are created like mass created factory products on an assembly line. They are made in a certain way and the big corporations have a planned method of turning out its product.
They believe that products produced by the culture industry have standardized features within them all. And they believe there is nothing different or spontaneous about each individual one and that it has become a routine operation that can be done by anyone with the "specific formulae".
Adorno and Horkeimer both notice that most products released now days become standardized, relating to this Adorno has also said songs become more successful over time because of standards and because of carefully thought out sequences which frequently recur in songs like patterns. Which make the songs all similar in a certain way.
Adorno and Horkheimer also believe the culture industry allows people to become "masses" and be easily manipulated by capitalist corporations and authoritarian governments. They believe that they have control over the cultural norm. Which in my opinion is true, this can be seen all around the world as from when a small trend come out it starts to become the cultural norm because everyone has to have it for example a new pair of Nike shoes or even the iphone this is all being backed and pushed further by the big capitalist corporations who stand to make money from the cultural trends of the world.