Not a pro here, so just giving a half-arsed answer...
Maybe multiband compression is typically a last-in-chain type of thing where you want to get your out levels as high as possible without clipping, but you also want the signal compressed to make the quieter parts louder. So if the default was zero, the compression effect would just lower the loud parts, and overall lower output would not maximize the signal to noise ratio.
That’s my guess. If you want to make your stuff jump out in a mix, throw MBC last in chain, and even crank up to 9db instead of 6 for each band. You lose some dynamic range, but get a more in-your-face sound and more clarity of subtle finger stuff.
When I did amateur sound engineering for my band a while back, I figured out that doing this with various mastering tools to the overall mix made it sound way better for listening in a car. Maybe audiophile purists who want maximal dynamic range would disagree, but if you want a more radio sound, this will help you get there.
I don't see any other compressor defaulting to +6db on the makeup gain...Adjusting each band by the same amount is no different from turning the main block level (or your recorded track) up/down by that amount.
Bands at 0 dB would result in lower level when you engage the block, assuming you're sending enough level in to get any compression. 6 dB was probably chosen because it's a few dB above 0.
the MultiBand compressor does.I don't see any other compressor defaulting to +6db on the makeup gain...
Uhh... yeah? That's exactly what I said...the MultiBand compressor does.
I'm pretty sure the band levels are post comp and not pre comp, we have the threshold to dial in what you described.The +6 you are focusing on in the multiband compresssor is how much gain is applied *before* the compression. Turning up the pre-compression gain value here has the indirect effect of increasing how much the signal is compressed. Think of it as cranking up a signal level that would normally cause clipping, but then the compressor avoids the clipping in a more graceful way. So you can bring up the apparent sound of the quiet sections, the sound of your fingerprints on the strings, without causing the loud parts to be so loud that it fizzes out in clipping distortion.
Makeup gain, in contrast, is about increasing a signal level after it has been lowered through compression. So post-compression gain might reasonably default to zero meaning no added gain, or to a value that causes the signal to match the peak or rms levels before the compression... that would be a logical intention for a default makeup gain... or maybe just a target output level... the actual amount of gain required to do this would depend on how much the signal was compressed first.
So just like an amp can have a “pre” and “post” section with different consequences for the sound, the same rough idea applies here: one nerd knob controls gain before compression, and a different one controls gain after compression. They have different consequences for the sound.
Someone else correct me if I’m off in the weeds please
I don't see any other compressor defaulting to +6db on the makeup gain...
Still can't find a reason for it to add 6db on the default settings...That's probably because the MBC is a post-effect, where the other Compressor types are often used before the Amp.