Tag Archives: waves

Extracting audio from video. Without a microphone.

We’ve all winced at those scenes in CSI:Nowheresville when somebody in a lab coat ‘enhances’ an image until you can see the reflection of the room in the pupil of somebody’s eye, or whatever.

This video is like that. Clearly implausible, most likely witchcraft.

Alternatively, a group of researchers at MIT really have found a way of extracting temporal information from CMOS sensor skew, sufficient to reconstruct audio up to around the 400Hz range from pictures alone.

Damned impressive, even if ‘sorcery’ is a more plausible algorithm.


I threw this together last night to try out an arrangement for a practical demo Elin is planning to build for a new show at the Centre for Life. I thought it might find wider use than just us sitting on the sofa saying “Coo!”. To be fair, it already has found wider use: Rosy from Cambridge Science Centre is staying with us, and was also saying “Coo!”.

One of the things that’s rather hard to wrap your head around when looking at waves in water is that the individual bits of water don’t translate with the wave propagation. Which rather obviously has to be the case once you realise you’ve been staring at the waves coming towards you for quite some time and yet the sea (tides permitting) hasn’t swept you away. Nevertheless, it’s one of those situations where a diagram helps, and an animated diagram helps a lot.

So here’s that animated diagram. For anyone who cares about such things, I built this in Apple Motion: it’s one (rotating) object, replicated with a rotation shift, which makes it very easy to play with different arrangements. It’s particularly interesting when the movement discs overlap. Maybe I’ll build another animation of that…

Anyway, you’re welcome to use the clip, though you’ll want to download and use this high-definition version (3Mb .mov, right-click and ’Save target as…’, and all that). It should loop smoothly enough.

Acoustic levitation using standing waves

Most physics teachers will have to demonstrate standing waves at some point in the school year and there are a number of standard demonstrations which can be done with school lab equipment. When teaching about them, I also show videos of standing waves I can’t recreate in the classroom and the one above is a lovely addition to my resources for this topic. This video also reminded me of a piece of art I saw at the Tate Modern several years ago – Kinetic Construction (Standing Wave) – which was the first time I saw a Physics demonstration presented as “art”.