Is "audience" singular or plural?

Singular if you want to emphasise its homogeneity, plural if you want to emphasise its component parts.

Ooh, I learned something today: American and British English apparently differ on this.

From Grammar Girl (which I understand is an even more authoritative source than pop song lyrics):

Americans tend to treat collective nouns as single units, so it’s more common to use the singular verb unless you’re definitely talking about individuals (3). So in America you would be more likely to hear “The faculty is meeting today” than “The faculty are meeting today.” In British usage, however, it’s the opposite; it’s more common to use the plural verb (4). In fact, some sentences that are perfectly correct in Britain would be considered incorrect in America (3). Take “Cambridge are winning the boat race.” Although I spent my elementary-school years in London, I have been fully Americanized, so this sentence doesn’t sound right to me. As an American, I would say, “Cambridge is winning.”

[http://grammar.quickanddirtytips.com/collective-nouns.aspx]

When I was in school I was taught that collective nouns always take a singular.

The ever-popular Google Ngram shows "audience is" far more common than "audience are". http://books.google.com/ngrams/graph?content=audience+is%2Caudience+are&year_start=1800&year_end=2000&corpus=0&smoothing=3

Of course a collective noun can be pluralized: You can say, "Of the three audiences we have had at our concerts, one audience booed us off the stage and two audiences threw rocks." Just like "committee" is a collective noun, but it's quite reasonable to say, "Two new committees were formed yesterday."

It's a singular noun that represents a set of people, so I would use

How the audience demotivates players

but

How the people in the audience demotivate players