I'm looking for 3 solid suggestions of a piece of music approx. 30
seconds in duration played by solo violin to illustrate the words "the
sweetest sound ever heard"

It will be part  of a much longer composition most likely, and I need
to be steered to the general area of the composition to listen to.
Specific recordings are even better, so I can quickly buy online and
have a listen. It's classical I'm looking for, from Bach on let's say.
The piece of music needs to have something of a narrative arc, that
is, it needs to go someplace. It needs to be short, but the ending can
be edited.
It wants to be emotional, but not too sad. 

If you have 3 really good suggestions and illustrate your
understanding of at least what I am going for  I may ask the question
again just to get more good suggestions.

thanks. Hope to hear from you soon!

"Sweet sound" would tend to suggest romantic repertoire for the most
part, and I guess you would be wanting pieces to appeal to the widest
audience.
I don't know that you can get much of a musical arc from just 30
seconds though, you night want a little more. Also it is alittle
unclear whether you want strictly solo repertoire or merely something
with violin as principal solo intstrument.

But I would suggest:
The Lark Ascending by Vaughan Williams. 
The last minute or so is all solo violin on its own and includes the
main musical theme.
http://www.amazon.com/gp/product/B000004CVM

The Romance from The Gadfly by Shostakovich.
http://www.amazon.com/gp/product/B0000042F8

The Meditation from Thais by Massenet
In fact this last record contains several other candidates
http://www.amazon.com/gp/product/B0000041ZL

and if you don't mind arrangements for violin this companion recording
would also be well worth getting
http://www.amazon.com/gp/product/B0000DG06L