5 ms·

The problem of de-synchronized metronomes

19 points by nicolodev 5y ago

jfrankamp 5y ago
Fireflies solve this problem with only local knowledge... maybe a variation of the problem that attacks/constrains it in a similar way?
ars 5y ago
The physical metronomes are using phase, not frequency, to synchronize. On top of that, they all start off at approximately the same frequency. So just having a global average frequency is not the same thing. Specifically: They tick in one direction faster than the other, which causes them to slowly shift phase.
- oakwhiz 5y ago
  You've got me thinking about multiplying two imperfect oscillators together.
- nicolodev 5y ago
  Thanks for your contribution. I just wanted to add some context for the problem of N items that share a median value and they want to reach independently all the same value. :) Thanks for the specification!
seanhunter 5y ago
Steve Reich made a lot of music based on the phasing in and out of imperfect time sources in the 1970s. If you're interested, check out "Music for 18 Musicians", "It's Gonna Rain", "Come out to show them", and if memory serves "Pulses" (might have that title wrong) which is literally just a bunch of mechanical metronomes which go in and out of phase as they wind down.
- nicolodev 5y ago
  Thank you for the contribution! TIL :)
- BeFlatXIII 5y ago
  You were thinking of Gygöry Ligeti's "Poème symphonique"[0] in your last example there. Steve Reich did write "Pendulum Music"[1] where microphones are swung from cables over loudspeakers and the feedback goes in and out of phase as the microphones return to stillness. [0] https://www.youtube.com/watch?v=-mUv705xj3U https://www.youtube.com/watch?v=-mUv705xj3U [0] https://www.youtube.com/watch?v=fU6qDeJPT-w https://www.youtube.com/watch?v=fU6qDeJPT-w
  - seanhunter 5y ago
    Aah yes you're right on both of those of course. It was like 25years ago I studied 20th century music. So weird to think that...
technothrasher 5y ago
More related to metronomes coming into phase with each other than your semaphore problem, but... for your viewing pleasure: https://www.youtube.com/watch?v=e-c6S6SdkPo https://www.youtube.com/watch?v=e-c6S6SdkPo
Const-me 5y ago
When people simulating real-time physics, it's almost always a bad idea to use semaphores like that. Instead, all pieces of the systems are normally simulated in lockstep. If the system has sufficient computations, a simulation step can be parallelized to use multiple CPU cores, but they are synchronized at every timestep of the simulation. Otherwise it will inevitably fail, there are way too many reasons for unfairness in the scheduler: other processes, hyperthreading, NUMA, unequal cooling/throttling, and more.

19 points by nicolodev 5y ago

Fireflies solve this problem with only local knowledge... maybe a variation of the problem that attacks/constrains it in a similar way?

ars 5y ago

The physical metronomes are using phase, not frequency, to synchronize. On top of that, they all start off at approximately the same frequency. So just having a global average frequency is not the same thing. Specifically: They tick in one direction faster than the other, which causes them to slowly shift phase.

oakwhiz 5y ago
You've got me thinking about multiplying two imperfect oscillators together.
nicolodev 5y ago
Thanks for your contribution. I just wanted to add some context for the problem of N items that share a median value and they want to reach independently all the same value. :) Thanks for the specification!

seanhunter 5y ago

Steve Reich made a lot of music based on the phasing in and out of imperfect time sources in the 1970s. If you're interested, check out "Music for 18 Musicians", "It's Gonna Rain", "Come out to show them", and if memory serves "Pulses" (might have that title wrong) which is literally just a bunch of mechanical metronomes which go in and out of phase as they wind down.

nicolodev 5y ago
Thank you for the contribution! TIL :)
BeFlatXIII 5y ago
You were thinking of Gygöry Ligeti's "Poème symphonique"[0] in your last example there. Steve Reich did write "Pendulum Music"[1] where microphones are swung from cables over loudspeakers and the feedback goes in and out of phase as the microphones return to stillness. [0] https://www.youtube.com/watch?v=-mUv705xj3U https://www.youtube.com/watch?v=-mUv705xj3U [0] https://www.youtube.com/watch?v=fU6qDeJPT-w https://www.youtube.com/watch?v=fU6qDeJPT-w
- seanhunter 5y ago
  Aah yes you're right on both of those of course. It was like 25years ago I studied 20th century music. So weird to think that...

technothrasher 5y ago

More related to metronomes coming into phase with each other than your semaphore problem, but... for your viewing pleasure: https://www.youtube.com/watch?v=e-c6S6SdkPo https://www.youtube.com/watch?v=e-c6S6SdkPo

Const-me 5y ago

When people simulating real-time physics, it's almost always a bad idea to use semaphores like that. Instead, all pieces of the systems are normally simulated in lockstep. If the system has sufficient computations, a simulation step can be parallelized to use multiple CPU cores, but they are synchronized at every timestep of the simulation. Otherwise it will inevitably fail, there are way too many reasons for unfairness in the scheduler: other processes, hyperthreading, NUMA, unequal cooling/throttling, and more.