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Anything that can pick up a gunshot will also pick up false
positives such as: fireworks going off, automobiles backfiring, loud
motorcycles starting, and sometimes, basketballs bounced hard on the
street and baseballs hit with bats. That's why audio recording
& monitoring is useful during possible gunshot events.<br>
<br>
If all the event-datapoints are logged to a public map that anyone
can click to examine the data more closely, the risk of abuse of any
audio or video transmission or recording function is minimal,
because any abuse or non-essential use of audio/video will be found
and exposed quickly.<br>
<br>
With appropriate safeguards, audio & video will help catch
shooters. Safeguards would include a rolling record/erase that
stores a maximum of e.g. 15 minutes of recording, centered on the
event. With this you can see e.g. the car drive up before the
passenger shoots the pedestrian, or the souped-up motorcycle start
up with loud pops and a roar. The same actions that trigger saving
a recording for evidence, would also put information to that effect
on the datapoint on the map.<br>
<br>
The contract terms with the city (which should also be public)
should specify usage for evidence of violent crimes only, and that
any abuse of the recording capability (such as to pull over that
motorcycle driver for a loud exhaust system) would trigger a large
financial penalty. If the city gov is serious about stopping crime
rather than e.g. catching loud motorcycles and illegal fireworks,
the city should have no trouble signing a contract with those terms
& conditions. <br>
<br>
-G.<br>
<br>
<br>
=====<br>
<br>
<br>
<div class="moz-cite-prefix">On 14-03-14-Fri 5:46 PM, Steve Berl
wrote:<br>
</div>
<blockquote
cite="mid:CAB4gGnf=E4MdniF60mLTggxn1_a0b6A_DA19wMtMChag-raaMg@mail.gmail.com"
type="cite">It is a DSP problem that should already be solved. I
suspect google can turn up a lot of info. I suspect It can likely
be implemented on a little Linux board computer like a RaspberryPI
or similar. Add the cost of a microphone, GPS, and mesh networking
HW.
<div>
<br>
</div>
<div>Steve<br>
<br>
On Friday, March 14, 2014, Jake <<a moz-do-not-send="true"
href="mailto:jake@spaz.org">jake@spaz.org</a>> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
I'm glad somebody knows about this! however i would suggest
that it's not quite as simple to decide "when the big impulse
of sound starts" without waiting for it to end and then
choosing a peak event.<br>
<br>
the best i know how to do is a peak detector where you wait
for the slope of the amplitude to head downward after a
threshold is achieved, but i think we can do better, and i
think we would need to if we were going to achieve good
results. and the more versatile the analysis is better, to
reduce false alarms (!) and increase detection of events at
lower amplitudes.<br>
<br>
On Fri, 14 Mar 2014, Steve Berl wrote:<br>
<br>
<blockquote style="margin:0 0 0 .8ex;border-left:1px #ccc
solid;padding-left:1ex">
You don't need to record and transmit the audio at all. You
just need the time of when the big impulse of sound starts,
which you can do locally. Just transmit the<br>
time stamp. <br>
NTP has a lot of the logic built in to discipline a computer
clock to a few microseconds of UTC time. It works best
attached directly to a serial port. <br>
<br>
Steve<br>
<br>
On Friday, March 14, 2014, Jake <<a
moz-do-not-send="true">jake@spaz.org</a>> wrote:<br>
I think it would be a positive move. When you hear a
gunshot outside you want to believe it's far away, somebody
else's problem.<br>
<br>
when you can look at a website and see where the
gunshots have been over time, you can figure out if it is
your neighborhood, and decide to talk with your<br>
neighbors about it. Maybe everybody knows who it is
and nobody knows what to do about it. You can have subtle,
problem-solving conversations with people<br>
that the police obviously are not capable of.<br>
<br>
as for the timing data, i think GPS clock is necessary
to remain synchronized with all the other nodes (plus it
serves as a handy location resolver) but<br>
i'm not sure yet what is the right way to stamp the
audio data. My best guess would be to put the timestamp
into the audio stream as a second audio<br>
channel, so that the central processing computer can
sort it all out and pinpoint the source.<br>
<br>
I do think this would be a good opportunity to grow
the mesh network but i don't know if the mesh group would be
excited to do it this way.<br>
<br>
-jake<br>
<br>
On Sat, 15 Mar 2014, Hol Gaskill wrote:<br>
<br>
setting up a system like this would have a
powerful effect on the public safety narrative - if the
public is able to self-organize a better<br>
solution at a low cost and<br>
share the data directly with everyone, it makes
alot less sense for public officials to propose alternatives
wherein our freedoms are demanded<br>
in exchange for<br>
whatever degree of security is theoretically
offered. who's saying it has to be the police that respond?
if the data is made public people<br>
could show up and<br>
videotape or whatever, or reconsider going to
that area within the next hour, generally use that info
however they see fit.<br>
<br>
i think using gps clock signal or a realtime
clock IC such as a ds1307 we could get pretty good time
data. a condenser mic doing amplitude<br>
and spectral (audio range)<br>
analysis would be enough to check for gunshots,
maybe car crashes, sirens, etc, without storing or
transmitting the actual audio. could this<br>
be a potential optional<br>
addon module to the mesh nodes? <br>
<br>
<br>
on Mar 14, 2014, Patrik D'haeseleer <<a
moz-do-not-send="true">patrikd@gmail.com</a>> wrote:<br>
Very interesting! That $264,000/yr fee
does seem outrageous - once the system is installed, there
should be relatively little<br>
maintenance to keep it<br>
running.<br>
<br>
I wonder if the company will be disabling or
retrieving the microphones when the contract ends. It's
possible the city is only "leasing" the<br>
equipment. Or that<br>
the company has build in some sort of
self-destruct to prevent cities taking over the network
without them...<br>
FWIW, I do think ShotSpotter is a useful
technology, but it needs to be designed with some ethical
issues in mind (e.g. not collecting and<br>
transmitting more<br>
information than is required for its stated
purpose). I think that Sudo Room taking over and overhauling
the existing network in a completely<br>
open-source<br>
fashion would be a great thing to do. That way
people could satisfy themselves that the technology only
does what it claims to do.<br>
Patrik<br>
<br>
<br>
On Fri, Mar 14, 2014 at 3:23 PM, Jake <<a
moz-do-not-send="true">jake@spaz.org</a>> wrote:<br>
what do people think of the shotspotter
system installed in oakland?<br>
<br>
it's a network of microphones on telephone
poles, each with a GPS (for a precise clock) and a network
connection. When a gunshot-like<br>
sound is<br>
detected, they send the sound and its
precise timing to a central server that determines the
location of the shot, and tells the police<br>
to go there.<br>
<br>
some people have expressed concern that
the microphones are used to spy on people, but it would be
impossible to hear a conversation<br>
from the top of<br>
a telephone pole that wasnt already loud
enough to be heard inside nearby houses (or the phone in
your pocket).<br>
<br>
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<br>
<br>
-- <br>
-steve<br>
<br>
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