Re: Physics of the sound of footsteps

[Axel Roebel <Axel.Roebel@xxxxxxxx>]

On 21/01/2014 17:45, Linda Seltzer wrote:
> When we walk, we can hear our footsteps, even if we are walking barefoot
> on a soft surface.  However, the number of steps per second in walking is
> below the auditory range.  What is it about the impact with the ground
> that causes the auditory signal?  Are there papers on the acoustics of a
> footstep?
> 
> Thank you for any information.

We usually perceive each footstep individually, so there is no relation
to the number of steps per second and the fact that you hear the
footsteps. You would hear a single footstep similar as you hear a single
knock on the door. If due to physical conditions you don't hear a single
footstep, you wont here the sequence either.

Related to the second part of your question. I am not aware of any
papers on physics of footsteps, probably because the physical
explanation depends on the material that you step on.

In general there are multiple events emitting sound related
to a single footstep (that's why individual footsteps are probably
best treated as a randomly distributed superposition of micro events)

E.g. gravel stones move and collide if you step on them. Soft material
may make noise when compressed due to air circulating within the
material, or due to the fact that the material structure makes sound if
deformed, moreover you may have effects that parts of the skin of the
foot attaches and detaches form the surface, finally the foot may rub
the surface (like you move your hand over a table surface), and you may
also hear noise due to air moving when you put your foot and small
cavities may form between your skin and the surface where the air is
first compressed and then finally evades (This last point is probably
the one that makes the least sound in general but it is a potential
sound source).

So the hypothesis would be if you walk with a perfectly dry feet on a
rigid (no deformation) and very smooth (no noise generated by friction)
surface (a mirror) then you would not hear your footsteps.

Best
Axel

> Linda Seltzer
> 


-- 
Axel Roebel
Analysis/Synthesis Team, IRCAM
Phone: ++33-1-4478 4845 | Fax: ++33-1-4478 1540