A mono recording of the tones used before an announcement at an airport.
Two before after examples of random frequency modulation (reverbed). Reference ... http://www.freesound.org/forum/viewtopic.php?p=24852#24852
I made a sort of ringing sample in Adobe Audition, then applied an echo effect to it.
A 1-shot sample taken of harmonics of a Yamaha Eterna classical acoustic guitar, recorded with a CAD E100 microphone. Notes ...