here's another one for music music players,if playback of a recording and live sound different then why is it only when observers get ...?

Again, I don't know what point you are trying to make.

In the example you give, "the crowd" is "fooled" because when they see a singer appearing to sing in a situation where they expect them to be singing, they assume they are singing. The only time when most of them will doubt this is when it becomes obvious that they are miming. Many people will watch a band "performing" on TV and assume that they are actually playing despite the fact that it's quite obvious they are not - drum kit not mic'd, guitars not plugged in, amps not turned on etc. etc. They just don't question it. Ihave always assumed that, if a "performance" on TV sounds "just like the record", then I'm listening to the record!

Also, in the example you give, the audience can't know what the "singer" actually sounds like when singing "live". If they are lip-syncing for the whole concert then they have nothing to compare it too. They just assum that's what they sound like.

In the case of a "good" ainger who basically sounds like they do on record, there will be little, if any, difference between them singing "live" through a PA with compression, eq, effects etc. and a recording which has already had those effects etc. applied, being played through the same PA. usually, what you actually hear when a person sings at a live concert is pretty far removed from what you'd hear if they just sang in front of you.