3 ms·

Following the leads, DOI:10.1145/2742647.2742658 says the accelerometer in Apple iPhone 6, Google Nexus 5 and Samsung Galaxy S5 supports 4kHz sampling. However

Following the leads, DOI:10.1145/2742647.2742658 says the accelerometer in Apple iPhone 6, Google Nexus 5 and Samsung Galaxy S5 supports 4kHz sampling. However, the OS limits it to 200Hz to conserve power. Googling around, it appears there are accelerometers with much higher bandwidths. Here's how 8 bps mono speech at 4kHz sounds like: https://vocaroo.com/102J6NRULedu https://vocaroo.com/102J6NRULedu (download link: http://fpaste.dy.fi/oyU/dl http://fpaste.dy.fi/oyU/dl) Sounds pretty good. At 2kHz it gets a bit hard to listen to but I can still understand a fair proportion of it. I imagine it shouldn't be too hard to come up with an algorithm (or neural net) to resynthesize the higher frequencies and make it easier to understand. 2kHz sample: https://vocaroo.com/18F3LkYrsPNQ https://vocaroo.com/18F3LkYrsPNQ (download: http://fpaste.dy.fi/rvy/dl http://fpaste.dy.fi/rvy/dl) (Obviously these are not accelerometer recordings, just normal microphone recordings downsampled with sox) I agree it's a bit silly complaint though. I see it a lot in security circles: if some feature doesn't give you perfect protection against all possible attacks, it's a problem. At the same time, the same people advocate mitigations and techniques that only apply to certain attacks. It's as if there's no silver bullet, but it's a damn shame if you deploy something that isn't a silver bullet!

kop316 5y ago
https://crypto.stanford.edu/gyrophone/files/gyromic.pdf https://crypto.stanford.edu/gyrophone/files/gyromic.pdf So on this paper looking at it, the experiment is done where the speakers are at 75 dB and the phone is one foot away (See Section 3.4). 75 dB looks to be about as loud as a vacuum cleaner. The phone is also completely still, so there is no other data that is being recorded besides (very loud) audio. Good to know about the various phones though. I'm honestly not sure why such a high sample rate is even needed/wanted (though in the paper, it is mentioned that there are ones with much lower sampling rates, so if this is a real concern, populate you device with a chip with a lower sampling rate).
- genewitch 5y ago
  The higher the sample rate the more fine grained movement it can detect, and, with decimation, the better the signal to noise ratio. MEMS stuff is really noisy because they're mechanical stuff is wobbly enough and the ADCs are pretty sensitive since the mechanical stuff is so small.
  - kop316 5y ago
    Heh, that's good to know, thanks! So how find grained can it detect like that? I would think with a phone, you are only looking for large movements (phone being g picked up, in an automobile, etc.)
    - genewitch 5y ago
      Sorry for the late reply: Accelerometers[0] are usually rated by the peak acceleration per second they can measure, say 8g/s. Gyroscopes apparently are now rated at degrees per second, so, 4000 degrees/s for example. The higher those numbers, the more time the ADC has to sample, be that on the sensor itself (digital output, say SPI, 1-wire, or serial) or an intermediary (arduino, ADC board with digital output) if the sensor is analog. The sensors in even mid-range cellphones is probably enough to determine what road you're driving on and how fast, judging by viewing the graph output form something like Torque Lite or some other sensor display app. I had some $12 9 degree of freedom sensor, gyroscope, accelerometer, compass (or something), and when displaying the combined gyro and accelerometer as a line on a graph you could watch me leave the room (footsteps, doors) walk all the way across the house, and turn off a loud radio. The sensor was on a desk. [0] https://www.adafruit.com/category/682 https://www.adafruit.com/category/682 P.S. the Bosch sensors are crazy. expensive, but if you can find a SoC board with a bosch (BNO is the part prefix) sensor for like $50, get it. Atomic Pi is one board that has a Bosch on, and it's barely over $35 itself!

kop316 5y ago

https://crypto.stanford.edu/gyrophone/files/gyromic.pdf https://crypto.stanford.edu/gyrophone/files/gyromic.pdf So on this paper looking at it, the experiment is done where the speakers are at 75 dB and the phone is one foot away (See Section 3.4). 75 dB looks to be about as loud as a vacuum cleaner. The phone is also completely still, so there is no other data that is being recorded besides (very loud) audio. Good to know about the various phones though. I'm honestly not sure why such a high sample rate is even needed/wanted (though in the paper, it is mentioned that there are ones with much lower sampling rates, so if this is a real concern, populate you device with a chip with a lower sampling rate).

genewitch 5y ago
The higher the sample rate the more fine grained movement it can detect, and, with decimation, the better the signal to noise ratio. MEMS stuff is really noisy because they're mechanical stuff is wobbly enough and the ADCs are pretty sensitive since the mechanical stuff is so small.
- kop316 5y ago
  Heh, that's good to know, thanks! So how find grained can it detect like that? I would think with a phone, you are only looking for large movements (phone being g picked up, in an automobile, etc.)
  - genewitch 5y ago
    Sorry for the late reply: Accelerometers[0] are usually rated by the peak acceleration per second they can measure, say 8g/s. Gyroscopes apparently are now rated at degrees per second, so, 4000 degrees/s for example. The higher those numbers, the more time the ADC has to sample, be that on the sensor itself (digital output, say SPI, 1-wire, or serial) or an intermediary (arduino, ADC board with digital output) if the sensor is analog. The sensors in even mid-range cellphones is probably enough to determine what road you're driving on and how fast, judging by viewing the graph output form something like Torque Lite or some other sensor display app. I had some $12 9 degree of freedom sensor, gyroscope, accelerometer, compass (or something), and when displaying the combined gyro and accelerometer as a line on a graph you could watch me leave the room (footsteps, doors) walk all the way across the house, and turn off a loud radio. The sensor was on a desk. [0] https://www.adafruit.com/category/682 https://www.adafruit.com/category/682 P.S. the Bosch sensors are crazy. expensive, but if you can find a SoC board with a bosch (BNO is the part prefix) sensor for like $50, get it. Atomic Pi is one board that has a Bosch on, and it's barely over $35 itself!