That's fairly common and the simplest explanation I know about is that you can "memorize" a sound if you train for it and then when you hear it you recall the memory without going through the whole "pipeline" for understanding what it is. Your memory or "cache" for what C is indexes with the specific harmonics that make the timbre of a piano. On another instrument it's a different sound, the main harmonic is the same one but the timbre is so different that you need to go through the "let's use perfect pitch for this" part of your brain.

It's the same thing mechanics use to identify engine sounds quickly or why some people can tell who's walking on a hallway because of how the steps sound. Repeated exposition to a stimulus that then gets associated with something etches a memory.

This not only happens with perfect pitch. To for example know how to tell a major third from a minor third on all keys you can "memorize" all the sounds and know which one they are. I think my brain kinda did that and now I sometimes get confused with M3 and P5 because of how "similar" they sound even though you can like totally fit another tone comfortable between the root and the fifth and the root and the third don't have enough air for that.

My partner did her dissertation on exactly this.

If you are interested, see Chapter 3:

https://escholarship.org/uc/item/0rp5w2rd

Thank you! Primary instrument AP — 80% accuracy (C4 to B5), reaction time 1.81 seconds. Yet reduced by non primary instrument.

> Participants got significantly more trials correct when the timbre of the trials was congruent with the participant’s primary instrument (M = 39.13 (out of 48) trials, SD = 11.26) as opposed to incongruent with it (M = 36.5 (out of 48) trials, SD = 13.7), [t(23) = 2.935, p < .01].

Perfect pitch here too...

Curious if this happens to others - you’ll hear a noise (e.g a glass hitting something, an object falling to the ground etc) that makes a single tone, and a song immediately starts playing in your head because it starts with that same tone?

My stand up desk at an old job was the starting pitch to Beyoncé’s Crazy in Love

Not perfect pitch, but I play a fretless instrument. I learned to map specific intervals to songs.

    minor 2nd : Jaws
    major 2nd : Frere Jacques
    ...

Now every time I hear an interval these things enter my brain.

"My Bonnie lies under the ocean"

Yep... intervals helped during music exams :)

For me, its more that hearing any song for a few chord changes conjures up other songs in either the same key or with the same chord progression, independent of key.

I remember noticing in highschool that hitting a few different corrugated plastic gutter pipes in my backyard would allow playing the bass line to Crazy Train...in principle, i immediately recognize the notes to different beeps and alarms in daily life and think about it unconsciously.

Not perfect pitch, but yeah, this does happen to me. I'll hear a sound and start singing the rest of the song the sound reminds me of, and everyone will look at me oddly.

but the pitches on the piano are not perfect, aren't they ? It uses equal temperament iso just temperament. So shouldn't a piano sound out of key to you ?

That's not what perfect pitch means, per se. It should work with any tonal system.

Suppose you're calibrated to an G1 on 49Hz. You get exposed to a wave at 61.25Hz. Do you consider it to be a B ? For me, the major third on a piano sounds different ('off') from where I imagine it to be.

I don't know if it works by calibrating a note to a frequency, so much as being able to hear the intervals perfectly.... but I don't know for sure, my own pitch is only of modest quality