
Pre-Safe Sound: Playing ‘pink noise’ in the split second before impact (2015) - rosstex
https://www.mercedes-benz.com/en/mercedes-benz/next/connectivity/pre-safe-sound-playing-pink-noise-in-the-split-second-before-impact/
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ComputerGuru
This is a comment from Reddit on the same [0]; though I cannot vouch for its
veracity, I found it interesting nonetheless:

Former Benz master tech here.

I've spent a good bit of time diving into the nitty gritty of these systems.

It uses all of the vehicle sensors to determine crash logic.

You want to fire the pretensioners before the airbags if at all possible. This
locks the occupants in a much more secure and predictable psition.

Accelerometers can determine if something like a rollover is in progress.

Heavy braking + high speed + sudden activation of the parking sensors
indicates a crash before physical contact happens.

It can use the radar on distronic equipped cars to predict a crash.

If the vehicle is in a slide, and a sudden yaw correction happens, this means
a collision has occurred, even if the airbag sensors haven't been triggered.
This is useful because the airbag sensors are only good at detecting force in
one dimension.

It's even possible for the vehicle to determine to fire the pretensioners but
no airbags based on occupant size and weight (determined through seat/steering
wheel position and capacitive mats in the seats) and impact vectors.

It will even do things like full field the alternator up to 18+ volts to slam
the windows shut super fast in the event of a rollover.

The actual detection logic fills a 4" thick book.

It's a big reason those cars are so damn expensive.

Mercedes doesn't fuck around with safety.

If I had to be in a wreck, it would be in an S class. Hands down.

0:
[http://www.reddit.com/r/todayilearned/comments/59qhaw/til_ne...](http://www.reddit.com/r/todayilearned/comments/59qhaw/til_new_mercedesbenz_cars_will_play_a_short_blast/d9avtav)

~~~
3chelon
This is all fascinating stuff, thanks.

Of course, in the future when all cars are connected (even if they're not
self-driving), combining all this sensor data and sending it to the vehicles
behind you would save countless lives. The number of times you hear about
pile-ups in fog and heavy rain - that could all be avoided by cars talking to
each other.

But I'll bet there's still no open (or even closed) standard on inter-
manufacturer comms yet?

~~~
arethuza
That does raise interesting security problems though - my car receives a
message saying to stop as quickly as possible, how does it decide whether this
is a valid message or someone hacking cars for fun?

~~~
Splines
I don't have an answer for you, but maybe it stems from some sort of idea of
identity? Maybe the car sends a message authenticated with your license ID.
Cars are (hand waves) able to authenticate the validity of a message. If you
send a message saying you were in a collision, that comes with the side
effects of saying you were in a collision - emergency contacts and police may
be notified, maybe something pings cars registered to you to see if it was
actually in an accident based on sensor data. Your insurance rates may go up.
If it turns out you were lying, maybe your car gets flagged for repairs next
time you try to re-register your tags. Or maybe you are flagged for trolling
and you get the "boy who cried wolf" effect.

~~~
3chelon
Sure, the actual vehicle systems had better work and be properly
authenticated, and that could be achieved in numerous ways... but none of this
stops a hacker war-driving with a laptop, or sitting on an overhead bridge, or
on the other side of the world.

There is no doubt that intelligent highways would be a massive target for
terrorist and cyber attacks. However, one thing in our favour is the fact
there is so little technology already in place, since they won't be burdened
with decades' worth of insecure legacy systems: at least they'll be able to
start out building infrastructure in full knowledge that it better be secure.

~~~
athenot
I'm tempted to qualify the second point as optimist.

US voting machines didn't have to deal with legacy technology and still turned
pretty bad from an infosec POV.

~~~
mannykannot
Exactly, and it is not just this one case: serious, avoidable security cock-
ups have happened every time a new class of device has been put on the
internet, with the IoT DDOS debacle being perhaps the latest example.

------
codeulike
The interesting bit:

 _If an impending collision is detected that would be expected to produce a
loud crash, the vehicle’s sound system plays a short interference signal. This
causes the stapedius muscle in the ears to contract, which for a split second
changes the link between the eardrum and the inner ear and so better protects
it against high acoustic pressures. Most importantly, the reflex reduces the
damage to hearing._

~~~
Angostura
I wonder if it as cool hypothesis that they decided to implement as a cheap
bit of marketing, or whether the protective factor is actually evidence-based.

~~~
pja
Did you actually read the article, or are you just here to snark on HN?

Here, let me do your research for you. First link on a search for "stapedius
reflex" is
[https://en.wikipedia.org/wiki/Acoustic_reflex](https://en.wikipedia.org/wiki/Acoustic_reflex)

A quick search on Google Scholar for "acoustic reflex noise" turns up this
paper from _1962_ which states in the abstract that the acoustic reflex is
more easily triggered by wide bandwidth noise than a single sinusoidal tone.
[http://scitation.aip.org/content/asa/journal/jasa/34/9B/10.1...](http://scitation.aip.org/content/asa/journal/jasa/34/9B/10.1121/1.1918384)

I think we can safely say that this work is pretty evidence based.

~~~
fasteo
A friendly reminder: "a quick search on Google Scholar" is not research.

That paper you mention is just a functional description of the "accoustic
reflex". I don't think the parent comment was putting the existence of the
"accoustic reflex noise" in doubt; rather, and I agree with him, it's its
effectiveness to protect the driver in a car crash what is in doubt.

The page makes a reference to a human trial in 2011. It would be great if they
included a footnote with the reference to the actual paper.

~~~
pja
It’s not "research research" but it is "does this phenomenon actually exist in
the literature" research.

Insisting on testing the phenomenon in an actual car crash seems superfluous
to me. A car crash produces a loud noise that can potentially damage hearing,
which can be alleviated to some extent by triggering the acoustic reflex with
a quieter noise immediately before impact. So long as the generated noise is
well below the threshold of damage then I’m really failing to see why more
specific research is required in order to believe that this would be an
effective intervention.

~~~
semicolon_storm
The bit about the noise from a car crash being loud enough to damage hearing
after a one-time short exposure is what I doubt. Sure it's loud, but does a
split second exposure to it really do permanent damage? I don't know what the
answer is, but I am skeptical about the usefulness of this feature.

~~~
dogma1138
Stand by some one at the range without ear pro and ask them to shoot one shot.

The sound is only a fraction of a second but that ringing you'll hear is the
death sound of the frequency you'll likely never to be able to hear again.

You also need to understand that sound and loudness isn't what causes hearing
loss it's the pressure shockwave.

If a blast "noise" is mostly outside of your hearing range the pressure will
still do permanent damage.

When a bomb goes off most of the energy can very well be outside of the normal
frequency range of the human ear, it will still however rip your ears apart.

~~~
mark_kalvelage
_that ringing you 'll hear is the death sound of the frequency you'll likely
never to be able to hear again_

or you'll hear it all the time

------
hiharryhere
Forwarded this onto my dad who is an ENT specialist. He responded:

"The Stapedius reflex has been use for artillery gunners for decades but the
pink noise use is certainly novel."

~~~
arprocter
I was going to ask if this would work at the gun range

------
martin-adams
I worked with an audio engineer on real-time video encoding hardware and he
said that in audio compression, you can throw away audio data immediately
after a loud noise because the ear can't pick it up. This is probably an
oversimplification, but sounds like a similar technique in this safety
feature. I like it.

~~~
kimburgess
This is actually a big part of how MP3 compression works. Rather than using
straight up data compression, it uses a psychoacoustic model to simplify
different components of the signal that are affected by masking.

There's a nice high-level (human readable) technical overview here if you'd
like to learn more: [http://arstechnica.com/features/2007/10/the-audiofile-
unders...](http://arstechnica.com/features/2007/10/the-audiofile-
understanding-mp3-compression/)

~~~
kimburgess
I should add, as another side note / rabbit hole to those new to the art of
'fucking with brains through audio' — masking is also frequently put to use in
mixing, particularly EDM and more percussive genres.

To help squeeze every last drop of perceived dynamic range out of a track you
can use a technique known as sidechain compression
([http://samplesfrommars.com/blogs/tips-tricks/18999227-how-
to...](http://samplesfrommars.com/blogs/tips-tricks/18999227-how-to-use-
sidechain-compression-to-make-kicks-cut-through-the-mix)) to dynamically
compress other components of the mix in response to (usually) a kick drum.

~~~
ttctciyf
Thanks for that informative link.. I would say the advice to simply re-write a
musical composition so that bass and kick don't happen at the same time seems
to put the cart of mix aesthetics before the horse of musical intent! :)

"Sideband compression" sounds like an interesting dsp project! But I think the
term is "sidechain compression", right?

~~~
golergka
In electronic music, mix aesthetics is quite often exactly the musical intent
- you're trying to create a track that sounds a certain way first, and think
about melodies and harmonies (if you even have them) second. You would often
pick specific key and bassline because of how low frequencies (55-110 Hz
octave and below) sound in the mix on your intended equipment. You would even
distinguish between open-air and club tracks sometimes because of how open
space affects sonic qualities of your mix.

------
JHHuijnen
Dear everyone,

Mercedes is a good marketeer and with best intentions they included protection
of hearing in their campaign. I wouldn't blame them for not knowing and after
having spent lot's of money on this it could be dissapointing to hear that in
fact, the acoustic reflex arc, otherwise known as the stapedius reflex does
not protect hearing against loud sounds. It is simply a myth that even among
many professionals is believed.

The facts are that the ear's transparency for sounds is traditionally tested
with only a single frequency, around 226 Hz, and around that frequency the
sound levels get reduced by the acoustic reflex. Thus it seems as if the ear
protects itself for loud sounds and the myth is born although it has only been
measured at a single frequency.

Technology to measure the same prinicples for a wider frequency range is
currently only available for a selective group of researchers and for the
industry developing medical instruments in this direction (for which I work).
We know that above 1000 Hz the stapedius reflex is doing the opposite of
protection. It will increase the sound levels.

I could explain why the reflex is doing this, why did it evolve like this
during the last many thousands of years. It is certainly easy to understand
that a couple of hundred years ago (before industrialization) no protection
for loud sounds was actually needed and thus hearing protection is not a
logical candidate for explaining why we have such acoustic reflex...

Though this is not the point. The point is that Mercedes' feature is not
protecting your hearing during a collision impact. They made it with best
intentions and for that they deserve a compliment and credits.

A little more info about the acoustic reflex that I consider to be correct can
be found here:
[https://youtu.be/3a3Eeuhkh-c?t=1164](https://youtu.be/3a3Eeuhkh-c?t=1164)

Feel free to try to get in touch with me as well if you want to find out more
about this topic.

Cheers Jos

------
lordelph
Mildly interesting: when I played the sample pink noise in the article, my dog
went mental.

~~~
buserror
Of course he did. Poor thing, he realized you were going to be involved in a
car crash in the next 100ms.

(sorry couldn't resist :-))

------
rrmm
I wonder if that noise is going to be a major ptsd trigger for people involved
in an accident afterwards. (Of course probably any loud noise would be). It
will be interesting to see any data they can collect out of this on the
benefit in practice.

------
gururise
Fascinating stuff. Kudos to Mercedes-Benz for pushing the envelope and making
driving safer.

------
Stenzel
The pink noise in the video has some strange dropouts and is compressed. If
you want to listen to real pink noise I suggest this:
[http://stenzel.waldorfmusic.de/post/pink/](http://stenzel.waldorfmusic.de/post/pink/)
Source Code:
[https://github.com/Stenzel/newshadeofpink](https://github.com/Stenzel/newshadeofpink)
disclaimer: I made this.

------
cpeterso
I often listen to pink noise while I work to suppress room noise and mask
tinnitus. Ironically, I find it is also good for relieving headaches! :) I
have a CD with hour-long tracks of just white noise (sounds like static), pink
noise (sounds like waves), and brown noise (sounds like airplane hum).

[http://whitenoisemeditation.bandcamp.com/](http://whitenoisemeditation.bandcamp.com/)

~~~
audeyisaacs
You can also use SoX!

`[audey@feather ~]$ play -c2 -n synth whitenoise lowpass 400 highpass 40`

------
smegel
Sounds more like white noise to me. What makes it pink??

~~~
eyuelt
Redshift

~~~
leblancfg
The sound is distinctly crisper on BigQuery, though. Of course, cables can
make a difference but not always -- use CAT-8.2 if possible.

