Here’s the rub… create a BIAB recording (or use a commercial backing track) you’re basically functionally back to using SMF’s. Start at the beginning (very few arrangers can jump around within the file like many computer programs can) play to the end. Period.
No opportunity to mess with the song, no chance to change structure (add extra solos etc), no medleys on the fly, no easy transposition to different keys (again, few arrangers have really high quality file transposition, change more than one half step, quality drops off radically).
Decades ago, most arranger players decided to use the arranger rather than a decent workstation for its on the fly flexibility. Even back then, you lost a bit of quality compared to a good WS, and even today you lost a bit of editing flexibility. But nothing else allowed you freedom to improvise better than the arranger.
Using BIAB to make tracks using real audio parts has been around for decades. And the results have long surpassed the arranger. But you can’t play it live. So this seems to be useful by those that use mostly tracks.
Nowadays, compared to when Real Tracks came out, there has been a radical drop in the price of high quality multitrack files. To the point of perhaps working out cheaper than BIAB with a whole slew of Real Tracks packs. Depending on how many you have the time to make, or how fast you think you’d pick up the complexities of the program (and have a fast enough computer to deal with multiple real audio tracks) you may end up spending a ton more than you’d have done shopping around the backing track sites.
Don’t get me wrong, I’ve always had a soft spot for BIAB from its first days as a MIDI only track generator. But the scenery has changed since the 90’s (it came out in 1990 and ran on PC and my great Atari ST) and it faces a lot more challenges and has ballooned in price massively when you go get those Real Tracks..!
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An arranger is just a tool. What matters is what you build with it..!