Heard about this the other day in Physics and looked up a bit more about it. This is like the audio equivalent of Escher's never-ending staircase - successive tones that seem to always to go down in pitch forever, without getting any lower.
Risset accelerando
Wikipedia article - click the sound file at the bottom for a glissando

I thought it was quite cool, it fools the ears into thinking they're hearing something which they aren't. And out of general curiosity, could someone with perfect pitch tell me if it works for them.

edit - this one's quite nice too

Yes, it works. Although, if I fight it, I can jump up and down the octaves of the notes I'm hearing.

Oh okay. Just wondered if it would make a difference

I listened for a while, before it got too annoying and could only hear it rising. What is it supposed to sound like? I have not read the article yet.

It's supposed to sound continually rising but it never goes out of your range of hearing, because it's not actually rising the whole time - you just think it is.

I'm a bit confused, it's supposed to sound like it's continually rising or falling depending on which one you're listening to, yes? To me it sounds like a series of rises or falls, for example dropping from high to low gradually, then a leap, then another drop... the descending glissando is, to my ear, more effective and smoother, but I can hear octave jumps or something happening in there, and can definitely hear that the falling starts from higher up every so often... um... that makes no sense... (why am I not in bed??!) I think I can hear what the illusion is but I can also quite clearly hear how it's done if that makes sense... The one with the beat I would say the "jumps" are more obvious. I have to say I don't understand the science at ALL maybe I should try again tomorrow...

I can't make the Wiki one work... it won't play ogg files on my pc

Interesting....... *is slightly confused* I wonder if knowing there is a "trick" makes it easier to pick out?

I just listened to the first one. It sounded to me as thought the pitch rose and then the octave below was gradually introduced at the same time, then the upper pitch gradually disappeared and left the lower pitch rising.

Couldn't get the second one to play

You both obviously have better ears than me. That is (I think) how it's done, playing descending octaves and then jumping the bottom one up when it gets low. Maybe it works better if you're not listening too hard...

OK I guessed that must be how it was done, from what I heard, something like that. The science bit was way over my head!

I'll have a listen today now I'm a bit more awake - see if it makes any difference...

edit: Just been reading the Wiki article again, I think that one with the beat is also supposed to sound like it keeps getting faster as well as higher - to me that does sound like it's getting faster but then suddenly I think "hold on, it's got slower" but I can't hear the transition, or haven't managed to - anyone else?

With the glissando one I can just about make myself hear the illusion but actually seem to have to concentrate to hear it, rather than the other way around....

You can hear, if you try, on the second one the higher frequency cutting in.

I can hear that - it's letting myself hear the illusion I have a problem with

Maybe I'm just weird.....

What is the bottom link supposed to be? I just heard a really low murmur (sp?)

On the first one it sounded like it was getting faster but when I started listening it sounded the same. I heard the pitch go higher then drop the octave and start again but there was still the other note ascending, but then the other note got too high and went !

I couldn't get the second one to work

The last link is very quiet - I had to turn the volume up to hear it (it's a gliss)

this is interesting - the effect of sound resonance on rice