Accoustic Gunshot Analysis

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The current event is to study, upgrade and apply this technology:

Forensic Gunshot Accoustic Analysis is Heating Up
https://www.forensicmag.com/article...ot-accoustic-analysis-heating-dont-get-burned

 

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https://www.forensicmag.com/article...ot-accoustic-analysis-heating-dont-get-burned

 

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' " The ubiquitous availability of audio-capable mobile devices indicates that audio evidence will more frequently be part of forensic investigations," said gunshot accoustic expert Robert Maher, the head of Montana State University's Electrical and Computer Engineering Department. Maher first became interested in forensic gunshot accoustics after a conversation with a defense attorney regarding a who-shot-first question based on an emergency call center recording.'

 

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'Steven Beck, principal scientist at BAE Systems, along with FBI agents Hirotaka Nakasone and Kenneth Marr, performed gunshot accoustic studies in a controlled environment by placing microphones at a range of angles and distances from each blast in order to capture the sound pattern of a single round from multiple points of view. Gunshots produce two different sounds -- a "bang," caused by rapid expansion of gasses that push the bullet through the barrel, and a "crack," caused by shock waves in the air made by supersonic bullets.....Beck said analysts need to understand the underlying accoustics of impulse sounds, and then know what variations can occur and how the recording conditions can affect the signals.
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According to this research, a shot fired into the air produces a wildly different waveform from one fired in the direction of a recorder, even when both shots came from the same gun. Likewise, a heavy rifle blast fired at a great distance from the microphone can produce a sound signature that is almost indistinguishable from one produced by a smaller, lighter gun fired at c;lose range.

There was another surprise -- a bonus "bang" caught by recorders positioned at 90-degree angles to the barrel. The Beck team traced thios sound to gasses leaking and expanding out the side of certain types of firearms. This means investigators could potentially exploit this extra "bang" to identify the direction of the weapon from the recording device....more recent work has shown that sound level and waveform details between on-[axis and off-axis recordings of the same firearm are often significantly greater than the difference between two firearm types at the same azimuth.
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Maher said if the mobile device is located near the shooting position, the high level sound of the gunshot will typically overload the microphone, input amplifier, and related electronics, resulting in a severely clipped and distorted waveform. Then this distorted gunshot signal is presented to the device's audio coding system, which is usually a speech coder designed to represent intelligible speech, not gunshots and highly distorted waveforms. "Thus, interpretation of gunshot accoustic evidence that has been passed though a cell phone's audio system is an area in need of further research," he said.

"In situations where a relatively pristine recording is obtained there may be opportunities to identify useful forensic features from gunshot recording, but in most real-world cases the quality of the recorded waveform will be poor," he said.
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"If more than one recording is available, such as multiple devices in different locations capturing the same event, it may be feasible to reconstruct the most plausible location of the firearm and its orientation," he said.'

The apparatus would be sequentially placed along hallways and stairwells, which either-or plausibility would activate alarms and automatic partitions.

 

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Here are ten different bullet types analysed, which technology can also be adapted to bark beetle chirps (237 Hz):

Directional Aspects of Forensic Gunshot Recordings
www.montana.edu/maher/publications/maher_aesconf_0610_1-6.pdf
'....6.) 10mm handgun, Glock 20 '

 

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This early report includes the connection to TRACOR Applied Sciences, Austin, Texas:

Jul/Aug 1998: Signal Convolution of Recorded Free-Field Gunshot Sounds
www.aes.org/e-lib/browse.cfm?elib=12136

 

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Obviously, geometric parameters of a school hallway would apply to gunshot analysis, but also implicate an instant database retrieval of the type of gun nationally registered, within a few seconds, for example, a Glock 20.

Deciphering Gunshot Recordings
www.montana.edu/maher/publications/maher_aesconf_0608_1-8.pdf
'....Figure 1. Shock Wave Geometry for a Supersonic Mach 3 Projectile'

 

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Forensic Gunshot Accoustic Analysis
'If someone fires a weapon in the Federal Reserve Bank in San Francisco, a gunshot detection system instantly locks all security doors, trapping the shooter inside In metro areas of cities like Tucson,Los Angeles,and elsewhere, when a shot is fired, within one second of weapon discharge accoustic sensors stationed in strategic urban locations pick up the sound, automatically determine range and bearing, then notify authorities.'

Signal clipping is a problem to address, and pointing to some problematic areas for improvement, there is....

'Note that the recording reveals the muzzle blast
arrival and the overlapping arrival of the muzzle blast ground reflection, but no shock wave because the bullet speed was less than the speed of sound.....the gunshot sound field near the shooting position is generally quite well defined for the arrival of the direct sound of the muzzle blast and the ballistic shock wave if the projectile is supersonic. The timing and behavior of these initial sonic events are well predicted by geometrical accoustics. However, once the sound field includes first and higher-order reflections and reverberation, the sonic signature is less easily deciphered due to its dependence upon the accoustical surroundings that are typically independent of the firearm itself.'
(Deciphering Gunshot Recordings)

 

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Oops!

It is not known if the Columbine shooting, for example, took place before the San Francisco Federal Reserve Bank installed a gunshot-detection system, though there is evidence that this technology is being deliberately reserved for the 'elite' of capitalism:

Sound Measuring Gunshot Noise Level
www.trapshooters.com/threads/sound-measuring-gunshot-noise-level.260477/
'....LXT1-QPR....'

How Loud Are Weapons?

AR15 .223 caliber 162-3 dB (164 dB M4)
P228 9mm 159-162 dB
P229 .40 S&W 161-2 dB
P229 .357 SIG 162-3 dB

When reviewing the decibel meters available, the dB range is not high enough, withy a cut-off at around 130-140 dB.

Electronics 101: Decibel Meter Circuits
www.discovercircuits.com/D/decibel.htm
'....Responds to sound pressure levels from about 60-70 dB.'

Sensors mounted in the ceiling would detect gunshot bursts and also their vandalism. An oscillosope in every school?

 

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One must click to find installation dates on the webpage:

Safety Dynamic's SENTRI Gunshot Detection Protects Federal Reserve Bank in San Francisco
safetydynamics.net/index.html

 

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USMB software does not like the Safety Dynamics URL.

 

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In the report above: ' Baltimore: "What the city is looking for is a gunshot technology that can identify a gunshot and not alert when there's other noise," said Goldstein.'

School-ceiling mounted units would already be able to filter out "echo flutter" in hallways and stairwells, which filtering system could be coupled to an oscilloscope for further real-time analysis of the milliseconds time-window of a muzzle blast. C-weighting is the likely approach, because it measures sound pressure levels above 85 dB, which approach would also filter the loudest human voice (135 dB) from say, a 22. caliber weapon. A police-station grid would light up showing the precise location in or around the school, though first responder presence is the priority (teacher, principal, janitor, shrink, or automatically activated bullet-proof partitioning backed up by hired security, etc).

 

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4 Oct 2017 Police Chief Talks Gunshot Detection
Police chief talks gunshot detection, Tasers | | Arizona Public Safety Coalition
'....The system guarantees detection within 75 feet....they are set to detect frequencies of gunshots but no other sounds such as nearby conversations....'

 

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SENTRI system page: 'shots fired, boom, the cameras turn....The unit employs neural networks, so it can listen for the temporal pattern of a gunshot and ignore similar sounds, like a bus backfire.'

One system allows the shooter the chance to escape and does not partition off the building:

Guardian Indoor Shooter Detection System

 

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The system in post #14 allows the shooter to exit the building and remain at large, which will not suffice. The one installed at the Federal Reserve Bank in San Francisco does not allow the shooter to escape. Even if suicidal, perpetrators and shooters in the future cannot be assured that they will not realize their worst nightmare, which is to be captured alive.

Gunshot-activated partitions seem the most intelligent trajectory to pursue, and cooking oil drops the shooter immediately, no exceptions.

 

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To trump the inherent pathology of the 2nd Amendment, gunshot detectors and partitions concentrated on the crucial first floor would include bullet-proof portable partitions on wheels that can be used by an armed teacher, janitor, etc. The partition would allow bullet-proof sighting capability along with shooting capability, because the shooter may enter from a window rather than a door. This approach also considers the possibility that the gun(s) was smuggled into the building previous to the shooting. More teachers may want to be armed if they had partitions.