After posting the "definition" of a mute, it occurred to me that the added weight is reducing the magnitude of the high frequency components of the note. With a bit of further search, a video on YouTube confirmed my opinion.

With a "performance mute, reducing the higher frequencies makes the sound less piercing, which is what "cuts" into the ears of listeners, for better or worse depending on the composer and player's intention. This is more change of tone than of volume.

With a "practice mute, the lower frequencies are also more easily absorbed by walls and furnishings like curtains and upholstery, thus providing more isolation of the practicing fiddler from friends and family.

A mute probably won't work with a dulcimer because the bridge-stick combination is already heavy.

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To my ears, I hear a mute on a violin as making it sound a little more 'hollow' with a quality not unlike an old gramophone or like a medieval crumhorn or shawm. Personally, i really like that sound. 

Wally,that's it,the particular mute I used is some hard,dark wood shaped like a big-toothed double comb.Takes the "shrill" out of the violin.Beth,you may be amused that in my youth I used clothes pegs(the kind with the metal spring) clamped to the sides of the bridge to have mercy on my roomates while I was learning the fiddle...

A mute for a string instrument is a small weight clipped on to the bridge of the instrument. It lowers the volume and changes the tone.

Google "violin mute" for pictures and lots more information.

A "muted fiddle" is a violin with a mute installed on it.

Can I ask a daft question? What's a muted fiddle?

That's funny Robin,but now that you mention it,I can hear the similarities!(Scotland the Brave).

Got that wrong re the tuning!The drones are D g dd,that enables the G-D bass on the 1st half of the 2nd. verse.

Pretty doggone cool, Jamie!  Maybe it's because I just heard Scotland the Brave recently, I feel like I'm hearing a little snippet of that trad tune in yours.