CHAT: IPA Question

Fellow Conlangers:

Please pardon my ignorance, and forgive me if the answer to this has been in a
thread that I missed.

IPA symbols represent a certain sound. I always see them defined (informally)
in terms of the way words in a certain languge sound, e.g., "[symbol] = the
sound of 'ng' in 'sing.' "  Now, obviously, different speakers of a language
may pronounce the same word quite differently. How do the formal definitions
for the IPA character sounds (whatever those definitions are) account for this
problem? Is there, for example, a "standard" audiotape of  each IPA sound, to
which other sounds can be compared?

Take Care,

Adam