I am not entirely sure what makes a tribute band different from any cover band. It's just a cover band by a specific original band. Just like the Elvis or Beatles impersonators. Mostly of bands that aren't around anymore. I went to see that Swedish P-Floyd tribute band the other year. Free concert, well attended. However, while they sure could play the parts, sometimes - and more often than not - I couldn't helpt but notice a certain "hack" mentality or "orchestra-pit-band-backing-up-someone-else" flair to it. You know, an orchestral band in a pit can back up Frank Sinatra, and the audience couldn't give a ***** about it, as long as they play it to a tee. Some kind of Swedish "dance-foxtrot-restaurant-" music. A certain amount of anonymity crept in, at all times.
I thought that some kind of progressive music, say, like Genesis "Lamb Lies Down On Broadway" are supposed to be something like of a musical. Albeit rock. And musicals they run for a long time, with different lead singers in the lead role, and way different orchestral bands. To the same success to the audience.
But when I saw that Canadian tribute act "Musical Box" perform that one in Hamburg some 10-12 years ago, I thought that it would be - basically - the same thing, as a regular musical. But it wasn't. Regardless of that "Musical Box" has been granted license and copyright to use original color slides as backdrop, and even costumes from Genesis management. They were sort of a "period" band. While I did think they cut it very well, there's something lacking in this "hungry" sound or "charged emotional vocals" that where present with the original artist. Peter Gabriels voice always had some gravitas, that even Phil Collins couldn't cover up later on. It just hadn't the same deep impact. And that deep impact can be lacking in the other instruments too, not just vocals.
To me, it's just like some kind of acting. While you can pull off anything convincingly enough, it's not... you. You speak another language with "accent" that can be detected.
I DO think it's ok though, that these bands are around and exists, because there are enough people who likes this stuff as an audience. These kinds of threads has been brought up before, when we start to speak of original bands, that has become tribute or cover bands of themselves, due to that no original members are part of it any more, but they're "original" in name only. Like Foreigner being the most striking example at the moment. I know that late Chris Squire of Yes, and even Gene Simmons worked/works a way out, with lawyers, to make Kiss / Yes I kind of franchise deal, that the bands, and names can continues long after any of the original members has gone. I mean gone, as in passed on, and not around us anymore. Not just leaving the band.
I think this "tribute" industry has been a valid force to be reckon with, since it a few decades ago, all of a sudden, was more accepted for musicians to start to sound like someone else and that has been regarded as a highly sought after trait. That one beats me, really. In jazz, Jaco was the most blatant thing to copy.
But still to me, which p*sses some of these bands off, I tell them up front "Just a cover band, anyway".
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EDIT: Those Pink Floyd tributes bands, seems to come here ever as often. Brit Floyd, Australian Pink Floyd Show, etc, that swedish P-Floyd (uncanny name since the first letter really has to be pronounced "Pee...!") and there's a cartoonish novelty act that used to be around to mock that pretentiousness and make punk parody version of Floyd tunes, of course, called Punk Floyd.