[sudo-discuss] shotspotter will be discontinued

[Steve Berl]

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.

Steve

On Friday, March 14, 2014, Jake <jake at spaz.org> wrote:

> 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.
>
> 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.
>
> On Fri, 14 Mar 2014, Steve Berl wrote:
>
>  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
> time stamp.
> 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.
>
> Steve
>
> On Friday, March 14, 2014, Jake <jake at spaz.org> wrote:
>       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.
>
>       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
>       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
>       that the police obviously are not capable of.
>
>       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
>       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
>       channel, so that the central processing computer can sort it all out
> and pinpoint the source.
>
>       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.
>
>       -jake
>
>       On Sat, 15 Mar 2014, Hol Gaskill wrote:
>
>             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
>             solution at a low cost and
>             share the data directly with everyone, it makes alot less
> sense for public officials to propose alternatives wherein our freedoms are
> demanded
>             in exchange for
>             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
>             could show up and
>             videotape or whatever, or reconsider going to that area within
> the next hour, generally use that info however they see fit.
>
>             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
>             and spectral (audio range)
>             analysis would be enough to check for gunshots, maybe car
> crashes, sirens, etc, without storing or transmitting the actual audio.
>  could this
>             be a potential optional
>             addon module to the mesh nodes?
>
>
>             on Mar 14, 2014, Patrik D'haeseleer <patrikd at gmail.com> wrote:
>                   Very interesting! That $264,000/yr fee does seem
> outrageous - once the system is installed, there should be relatively little
>             maintenance to keep it
>                   running.
>
>             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
>             equipment. Or that
>             the company has build in some sort of self-destruct to prevent
> cities taking over the network without them...
>             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
>             transmitting more
>             information than is required for its stated purpose). I think
> that Sudo Room taking over and overhauling the existing network in a
> completely
>             open-source
>             fashion would be a great thing to do. That way people could
> satisfy themselves that the technology only does what it claims to do.
>             Patrik
>
>
>             On Fri, Mar 14, 2014 at 3:23 PM, Jake <jake at spaz.org> wrote:
>                   what do people think of the shotspotter system installed
> in oakland?
>
>                   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
>             sound is
>                   detected, they send the sound and its precise timing to
> a central server that determines the location of the shot, and tells the
> police
>             to go there.
>
>                   some people have expressed concern that the microphones
> are used to spy on people, but it would be impossible to hear a conversation
>             from the top of
>                   a telephone pole that wasnt already loud enough to be
> heard inside nearby houses (or the phone in your pocket).
>
>

-- 
-steve
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