6 ms·

Previously done a lot of research into firearm and explosive acoustics (and the DSP to locate and categorise) and can say this is a _hard_ problem. Military ve

Previously done a lot of research into firearm and explosive acoustics (and the DSP to locate and categorise) and can say this is a _hard_ problem. Military versions for use in wide open spaces have a much better chance than in urban areas. Less than five percent seems unlikely, but I wouldn't be surprised to hear "less than half the time".

hcfman 3y ago
Categorisation will certainly be error prone as there is so much similarity because fireworks and gunshots. The main difference I expect is the speed of the shockwave resulting in steeper spectrograms for gunshots. However, a steep spectrogram is essentially showing a large amount of high as well as low frequencies. The higher frequencies degrade very quickly over distance reducing the difference of a gunshot from a firework the more this degrades. Not finding evidence is a different problem, it could be as simple as using a revolver rather than a semi-auto that ejects the cartridges. In any case, it would be great to see independent testing of this problem by the sort of people in this forum and you can use the software I developed last year (https://github.com/hcfman/sbts-aru https://github.com/hcfman/sbts-aru) to do so. That software sets the time on the Raspberry Pi to have less than 1 microsecond of error, which is more than enough for any validation efforts.
- nonrandomstring 3y ago
  Categorisation is one problem. Localisation is the other.
- nonrandomstring 3y ago
  Nice work. PM me if you want to chat. Have you considered the possibilities with oversampling and adding more channels- now there are much cheaper 192kHz multi-chan ADCs on the market - these can be used with MEMS arrays. Then you can play with phase information much more freely.
  - hcfman 3y ago
    Will do. Interesting looking show you run btw.
nonrandomstring 3y ago
The frustrating problem with people down voting without any explanation is that simply ignoring the knowledge of experts and hiding whatever has emotionally enraged you does not further the discussion.
- bko 3y ago
  I think people don't "trust the experts" when they read the "experts" saying things like this: > The reader can probably infer how this coverage pattern relates to race and class in Albuquerque. It's not perfect, but the distance from your house to a ShotSpotter sensor correlates fairly well with your household income. The wealthier you are, the less surveilled you are. This sets off the bs alarms to me. The author knows this is a gross distortion of the rationale and is playing dumb. So what else are they lying about?
  - jncfhnb 3y ago
    Are you saying the quoted passage is a lie?
    - bko 3y ago
      There's two explanations: 1. Cops use enforcement on poor neighborhoods because they like to make their lives difficult and because they hate poor people 2. Cops use enforcement there because that's where the crimes take place Explanation 2 is so obviously much more likely that I can't take the person that purports reason #1 without acknowledging the other explanation. They're playing dumb.
      - jncfhnb 3y ago
        The answer is obviously 2. However that does not make the quoted passage a lie.
      - lolinder 3y ago
        Two thoughts: 1) Why is this conversation happening in this subthread? What does this have to do with nonrandomstring's experience in doing similar work for the military? 2) Nothing in the passage you quoted insinuates anything about the reasoning for surveiling poor neighborhoods more than rich. It simply points out that this is a thing that is happening. Earlier they said this: > Many assumed that ShotSpotter coverage was concentrated in disadvantaged parts of the city, an unsurprising outcome but one that could contribute to systemic overpolicing. It's unsurprising because that is where the crime tends to take place, but there's a valid concern raised that this is a self-fulfilling prophecy. I've read some highly political anti-police rants in the past few years, but this isn't one of them. The author barely makes their opinions known at all, and when they do they're very aware of the complexities.

hcfman 3y ago

Categorisation will certainly be error prone as there is so much similarity because fireworks and gunshots. The main difference I expect is the speed of the shockwave resulting in steeper spectrograms for gunshots. However, a steep spectrogram is essentially showing a large amount of high as well as low frequencies. The higher frequencies degrade very quickly over distance reducing the difference of a gunshot from a firework the more this degrades. Not finding evidence is a different problem, it could be as simple as using a revolver rather than a semi-auto that ejects the cartridges. In any case, it would be great to see independent testing of this problem by the sort of people in this forum and you can use the software I developed last year (https://github.com/hcfman/sbts-aru https://github.com/hcfman/sbts-aru) to do so. That software sets the time on the Raspberry Pi to have less than 1 microsecond of error, which is more than enough for any validation efforts.

nonrandomstring 3y ago
Categorisation is one problem. Localisation is the other.
nonrandomstring 3y ago
Nice work. PM me if you want to chat. Have you considered the possibilities with oversampling and adding more channels- now there are much cheaper 192kHz multi-chan ADCs on the market - these can be used with MEMS arrays. Then you can play with phase information much more freely.
- hcfman 3y ago
  Will do. Interesting looking show you run btw.

nonrandomstring 3y ago

The frustrating problem with people down voting without any explanation is that simply ignoring the knowledge of experts and hiding whatever has emotionally enraged you does not further the discussion.

bko 3y ago
I think people don't "trust the experts" when they read the "experts" saying things like this: > The reader can probably infer how this coverage pattern relates to race and class in Albuquerque. It's not perfect, but the distance from your house to a ShotSpotter sensor correlates fairly well with your household income. The wealthier you are, the less surveilled you are. This sets off the bs alarms to me. The author knows this is a gross distortion of the rationale and is playing dumb. So what else are they lying about?
- jncfhnb 3y ago
  Are you saying the quoted passage is a lie?
  - bko 3y ago
    There's two explanations: 1. Cops use enforcement on poor neighborhoods because they like to make their lives difficult and because they hate poor people 2. Cops use enforcement there because that's where the crimes take place Explanation 2 is so obviously much more likely that I can't take the person that purports reason #1 without acknowledging the other explanation. They're playing dumb.
    - jncfhnb 3y ago
      The answer is obviously 2. However that does not make the quoted passage a lie.
    - lolinder 3y ago
      Two thoughts: 1) Why is this conversation happening in this subthread? What does this have to do with nonrandomstring's experience in doing similar work for the military? 2) Nothing in the passage you quoted insinuates anything about the reasoning for surveiling poor neighborhoods more than rich. It simply points out that this is a thing that is happening. Earlier they said this: > Many assumed that ShotSpotter coverage was concentrated in disadvantaged parts of the city, an unsurprising outcome but one that could contribute to systemic overpolicing. It's unsurprising because that is where the crime tends to take place, but there's a valid concern raised that this is a self-fulfilling prophecy. I've read some highly political anti-police rants in the past few years, but this isn't one of them. The author barely makes their opinions known at all, and when they do they're very aware of the complexities.