You know that little ring on Facebook that sounds off when you get an incoming call? Here, it sounds like this:

Well, that's not an off-the-shelf sound effect. It is the Facebook ping, and it was very well considered.

We know this because that ping has a fan, and that fan asked on Quora, "How much research has gone into developing the Facebook ping sound? The sound is so pleasant sometimes that it makes me wonder how much effort has been put into its development."

A flattered former Facebooker named Everett Katigbak, who "designed most of the audio currently in the product," chimed in with a most comprehensive answer.

Let's start with the best part. The chord is an F Major 7 (Fmaj7), which means it is composed of four notes: F, A, C, and E. That the perfect ping sound also spelled FACE was a "serendipitous discovery."

The chord had the additional good qualities, in Katigbak's estimation, that it's "a jazz chord... less formal, improvisational, and has a positive feel to it" and "contains a few interesting intervals within the chord that have certain connotations, and these form the modules for other notifications." It was improvisational and easily extensible, you could say.

"The [interesting] intervals are: 2 major thirds, F-A, and C-E. The major third trill is what is used on old school telephones," he explained, embedding this video of an old-school phone ringing.

Within the common Fmaj7 framework, Katigbak also could find "a minor 3rd interval, A-C. Descending, this interval is the same used in the common doorbell (ding-dong), which conceptually reminded me of when a friend would show up at your house," he wrote. "It is also the quintessential 'DIINNNNEERRR' or 'LAASSSIIIEEE' call out, which again, is a very nostalgic pattern."