Shape of a room 'heard' by acoustic echoes

[dipsydoodle]

The shape of a room can be modelled using echoes produced from sound, new research has found.

Like bats who emit sounds in order to navigate, researchers can now plug sounds into a computer algorithm to map a room.

The team were able to build a full 3D image of a room using four microphones to record echoes bouncing off walls.

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The ability to use sounds to navigate the world, called echolocation, is already used by dolphins and bats. Though rare, some blind people have also been known to possess this skill.

http://www.bbc.co.uk/news/science-environment-22941278

[wandy]

1. This is new? Why your room matters.............

Why your room matters

The sound that you hear in any room is a combination of the direct sound that travels straight from your speakers to your ears, and the indirect reflected sound — the sound from your speakers that bounces off the walls, floor, ceiling, and furniture before it reaches your ears.

Reflected sounds can be both good and bad. The good part is that they make music and movie dialogue sound much fuller and louder than they would otherwise. If you've ever played your speakers outdoors where there are no walls to add reflections, you've probably noticed that they don't sound as good — thin and dull, with very little bass. Reflected sound can add a pleasant spaciousness to your sound.

The bad part is that these same reflections can also distort sound in a room by making certain notes sound louder while canceling out others. The result may be midrange and treble that's too bright and harsh or echoey, or bass notes that are boomy, with a muddy "one-note" quality that drowns out deep bass. Because these reflections arrive at your ears at different times than the sound from your speakers, the three-dimensional "soundstage" created by your speakers and the images of the instruments and singers may become vague or smeared.

http://www.crutchfield.com/S-CjD9pqWDolI/learn/learningcenter/home/speakers_roomacoustics.html







Of course in the old days you'd have to do the math by hand, which basically meant 'move stuff around till it sounds good'.

[napoleon_in_rags]

2. I love this work.

Acoustic stuff is how the working person can have fun with the mystery of waves. I worked on a lot of this stuff. I actually worked on this problem at a napkin sketch level. As I recall, suppose you have the signal as put at right at the speaker, called P (pure). Then you record at another point, called R (reverbed) and F = fourier transform and IF = inverse fourier transform then:
IF(F(P)*F(M)) = R #convolution
F(P) * F(M) = F(R)
F(M) = F(R)/F(P)
M = IF(F(R)/F(P))
M should be the reverb profile of the room, which can be convolved with other sounds electronic to give them the same reverb as the room. Multiple reverb profiles should be enough to build maps of room, if the mic locations are precisely known. But that's as far as I got with that napkin sketch. I'm glad some one did this, it has ramifications for audio recording and maybe even public safety.

edit: by * I mean multiply each sample with the other at the same spot, like dot product (but not summed) and my / I mean multiply by the reciprocal.