When talk show bands play an impromptu song, how do instantly play in the same key?

Question

When talk show bands play an impromptu song, how do instantly play in the same key?

In: Other

Answer 1

Thrre is also some stuff people do not know about.

There is 2 audio mixer or more. One for the band*, one for the audience. The one for tbe band is always on. They can strike a chord while the audience mixer is still muted. So it basically go: can you make a (here we go.. chord is played) song? (Audience mixer on) (they play). 

Note: often each musician/singers have their own different mixer because they do not want or need to hear everything, or have different preferences. The drummer will have a click track. Basically a metronome. The singer don’t care about clicks. He might want the instruments but mostly the guitar.