Ok, so you have a software sequencer, and two drum machines. One drum machine gets to stay on Earth, while the other is placed in a rocket set for the speed of light. You press play on the sequencer and both machines play the same beat at the same time, does the drum machine in the rocket play faster then the one on Earth by the time the speed of light is reached? Or will the beat stay the same in the rocket, but have gone through more sequences then the one on earth? Is it possible that nothing happens?
If you’re one the rocket, it would sound the same, and the timing would measure the same as on Earth. But if the rocket came back to Earth after a while, you’d find the rocket’s sequencer had played fewer loops, not more, than the one on Earth; time slows down as the speed of light is approached. I should also point out that the speed of light cannot actually be reached, since mass increases as speed increases and further acceleration becomes more and more difficult. I’ll leave it to others to fill in the details.
on the rocket
It depends on the soft-sequencer. If we’re talking about Cubase running on a WinXp machine vs. Atari Notator on an Atari ST, then that opens up a whole new quesiton of timing consistency.
You are just effectively using the sequencers as tick-tocking clocks. Due to time dilation, the rocket clock will run slow, ie. its beats will sound a little after the beats of the Earth sequencer, with the difference gradually accumulating until a whole beat is missed (or a whole bar, or a whole lifetime depending on how fast the rocket is - if you actually attained light-speed the rocket sequencer would literally stop as the entire universe’s lifetime passed in an instant around it).
Of course, the tempo on the rocket will sound exactly the same as it did on Earth: it is only after arriving back at Earth will the difference be apparent.