>Maybe she's trying to get the same amount of sound out of the muted instrument and is forcing it. You do have to adjust air pressure and lip a bit when you have a mute in - especially the cone mute that is often used for students (as opposed to bell mute)

Think about guys like Clyde McCoy and Bubber Miley who used plunger mutes manually. I never could figure out how those guys did it back then. You have to hold it and release it just right, or forget it. Maybe if I'd stuck with it longer...

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>>>>Ok, all you musicians out there. A mute should not change how the tone of a note sounds, just how loud. Right? We have a promising Alison Balsom here and when we put the mute in her trumpet, the notes tend to break and are not clean. I tried it as well with the same result. Take the mute out and they are good. It's a Humes & Berg student mute, if that matters. The corks are filed down much, but seems to be plenty of room for air to get through. I think the trumpet is a King (she's practicing now). Any ideas?
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>>>Brings back memories. Used to play a King and man I loved my mute. Do you mean the tone or the pitch? I think the tonal quality definitely changes - that's part of the idea of the mute - gives it kind of a funky, less brassy sound. Pitch shouldn't change at all. Listen to some old Harry James or Biederbecke when they use the mute.
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>>The notes actual crack and break. I think Alan may be onto something with the air being restricted. I'm going to look into other mutes that soften/mellow the tone.
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>>I thought it was amazing that I haven't picked-up a brass instrument in over 30 years, but I still remembered the scale. It's probably why I can't find my glasses half the time; no more room in the keppie!