>>>Why do parps come in different 'tunes'
Because it's vibration that causes sound. In the same way that you'll get a different note if you 'twang' a really taught rubber band than if you do the same thing to a loosely-stretched one, the note produced depends upon the taughtness of your anal sphincter, which varies depending upon (among other things) how much gas is present. Additional noise (at lower frequencies) might be created when the blast of gas passes over the 'inner' parts of your buttocks if they're clenched together.
>>>and scents?
Unless you eat the same thing for every meal there wil be different things being digested in your alimentary canal at different times; so there will be different combinations of gases produced, with different odours.
>>>Why do they disgust everyone else but please me?
http://www.huffingtonpost.co.uk/2014/11/11/why-do-we-like-the-smell-of-our-own-farts_n_6137990.html
>>>Even the Queen parps
But hopefully, like her earlier namesake, she will forgive others who do (but only after a suitable period of time). The historian, John Aubrey recorded this:
"'This Earle of Oxford, making of his low obeisance to Queen Elizabeth, happened to let a Fart, at which he was so abashed and ashamed that he went to Travell, 7 yeares. On his returne the Queen welcomed him home, and sayd, My Lord, I had forgott the Fart.'