I agree with all posted here. Just to add a couple of direct answers to Chickers' questions:
Still a bit confusing; let me know if it would correct to say---- "musette is a degree, or value of wet ?
I wouldn't say this. The only definite thing that can be said about the word "musette" is that it won't be applied to a dry-tuned setting. You might encounter the phrase "amount of musette" used colloquially to refer to amount of tremolo in a setting.
Is that correct ? Is that the tremolo I hear ? This would not be the same as the raspy sound, or gurgle sound ?
Raspy and gurgling sounds generally aren't seen as features, though some accordions do feature them, when in need of repair. The tremolo will sound like "beating" or "pulsing" but with the tone still clean and ringing. If you listen to a sustained note, you can actually time the beats and use that to determine the amount of tremolo. As the notes converge, the rate of beating will slow, and as the notes get further apart, the beating increases. This creates the effect Chrisrayner's poking fun at. Scottish tremolo tuning can be almost half a semitone apart, so the beats warble to a degree that I have heard variously described as "lovely," "nostalgic," "comical," "questionable," "unconscionable," and "criminal."
Then there is "true-musette". What is this tuning ?
That always refers to MMM (three mid-octave reeds) rather than MM. But it doesn't tell you anything about how wet it is, or how much beating you will hear. For example, my main box has a "light swing" tuned MMM (more than concert, less than swing - so on the dry side) that creates even less audible beating than its MM setting. The reason is what Glug and John both mentioned earlier: If you consider the three M reeds as M- (tuned down), M (roughly in the middle), and M+ (tuned up), the degree of wetness, or tremolo, will be determined by the difference between the M- and M+ reed. The middle M doesn't add tremolo - if anything, it decreases the perception of that tremolo.
Picture the two sine waves of the M- and M+ reed. They have slightly different frequencies, causing them to go in and out of phase. Each time two valleys or two peaks line up precisely, the listener perceives a "beat." When you add a third wave to the mix, it mitigates that effect. It would require all three waves aligning to hear a "beat" - and this will be much rarer with three waves. So MMM settings are sometimes used to help a very wet tuning sound a little more pleasant, and they're also sometimes used just to add richness and complexity to a drier tuning like light swing. I hope this demystifies it a bit!
