How do timestamps work?

thbar commented 7 years ago

First thanks for ex-portmidi, I'm starting to use it to play around with my synth & Elixir. I successfully managed to record sequences of events while playing the synth, which is already great :smile:

If I call PortMidi.write with a timestamp, it seems like the note is played right away, is it expected?

Here is a concrete example:

PortMidi.write(output, [
  {{144, 36, 55}, 13771},
  {{128, 36, 68}, 13919},
  {{144, 48, 64}, 14310},
  {{128, 48, 75}, 14453},
])

(in that case the 2 notes will stack up immediately).

I looked a bit inside the code and in the portmidi documentation, and read here:

timestamps are ignored if the stream was opened with latency = 0

This makes me wonder how timestamps work when called from ex-portmidi.

Did you manage to get them working on your side?

Thanks!

lucidstack commented 7 years ago

Hey there, thank you for trying out ex-portmidi, glad it's working (mostly!) for you 😀

Good catch there, I had totally missed that bit from the documentation, and just put latency at 0 by default when opening an output device. I'm now adding the option to set your own latency on open.

Will let you know when you can upgrade! 👌

lucidstack commented 7 years ago

@thbar done! 🎉

Feel free to pull the new version 5.1.0 from Hex. I have added a third optional argument to PortMidi.open/2,3 for latency, defaulting to 0. I've given it a try, and it seems to work okay! Check out the updated documentation if you need to.

Let me know how it goes! 👋

PS: I've mentioned you in the changelog for spotting the issue, I hope you don't mind! 😀

thbar commented 7 years ago

Thanks a bunch @lucidstack! I'll test this out and will report back & close here.

Happy to be in the changelog, no problem. Thanks again!

lucidstack / ex-portmidi

How do timestamps work? #6