6 ms·

I'd really like to know how this technology differentiates a gunshot from a car backfiring.

• nanomonkey 5y ago
  From my understanding, looking into making an open source version years ago, a human will actually listen to the audio clip and verify, plus there is some triangulation going on where they can determine the speed of the bullet and direction for at least high powered bullets using multiple microphones.
• throwaway0a5e 5y ago
  It's easy in a lab, in a city with potential for fairly arbitrary reverberations hitting the microphone at fairly arbitrary timings it's right up there with forensic fire analysis and other crap like that.
• sokoloff 5y ago
  I’d guess a backfire (or afterfire) is significantly subsonic and therefore probably has a different (less sharp) profile than gunshot report of typical ammunition.
  • darksaints 5y ago
    .45 ACP, which is probably the second most common pistol round, is subsonic by default.
    • CydeWeys 5y ago
      It's definitely not the second-most common pistol round, especially in crime. It's way below .22LR and 9mm. Might even be below .380 ACP, .38 Special, and .25 ACP too. The guns used in crime are quite different than the guns preferred by the enthusiast community -- they're generally older, smaller, and cheaper.
      • darksaints 5y ago
        .380 ACP, .38 special, and .25 ACP are also subsonic in their most commonly available rounds. As is .22LR as long as it is being shot out of a pistol (longer barrels will accelerate it past supersonic velocities, but almost all ammo is subsonic out of a pistol like a mark IV). According to this survey on guns used in crime, it is 9mm, followed by .40 S&W (a typically transonic round), and then .45ACP. https://oag.ca.gov/sites/all/files/agweb/pdfs/publications/firearms-report-16.pdf https://oag.ca.gov/sites/all/files/agweb/pdfs/publications/f...
• darksaints 5y ago
  It likely doesn't. In the article it mentions that it sends the Chicago PD on 60+ wild goose chases every day.
  • deleted 5y ago
    [deleted]
• SkyPuncher 5y ago
  I went to college in Flint. Hearing gunshots were not uncommon. You can tell the difference from a car backfire. At it's core the "chamber" size is different. This creates a different reverb pattern, sound pattern, and frequency. I'm guessing you could imagine the difference between slapping a surface of water vs concrete. The over noise will be dominated by the sound of your hand, but you can hear specifics for each. ---- Whether or not these systems can tell the difference, I'm not sure.
  • chasd00 5y ago
    i hear gunshots every.single.night ( live in Oak Cliff which is on the South side of downtown Dallas ). It's so annoying and then maybe 10% of the time you get the helicopter about 5min later. You can tell gunshots from car backfires because there's 4 or 5 of them in row. pop-pop-pop-pop-pop vs one low-rolling bang Edit: usually what this is is people leaving a bar/club and sticking their pistol out of their window on the way out of the parking lot. On a nice day with the windows open you'll hear the same when the Cowboys score a touchdown. basically impossible to catch/stop
• codechad 5y ago
• tzs 5y ago
  How often do cars backfire? The internet is telling me that fuel injection and computer controlled mixtures have made it rare in modern vehicles. Carburetors were largely gone from new cars by around 1990.
  • tyingq 5y ago
    Construction sounds might be a more common issue. Lots of nail guns use cartridge loads, for example. Or fireworks. Or impact hammers like you would use in a muffler shop, street jackhammers, etc.
  • avidiax 5y ago
    And then some hobbyist decides that backfiring is really cool, and tunes their vehicle to get that effect.
    • gcheong 5y ago
      It’s almost a daily occurrence around where I live in the San Francisco Outer Sunset suburbs.
  • coffeecat 5y ago
    It's relatively uncommon nowadays compared to the number of cars that don't backfire. But I certainly hear cars backfiring more frequently than I hear gunshots.