Splice sm-808 Implementation

Here's my implementation of the Splice SM-808 practice exercise

Few notes about this implementation:

• It's a rotating pattern grid with a moving cursor underneath it to indicate which step the drum machine is currently on. It's using terminal escape sequences to position the cursor - see song.go - playStep().

• Supports mixing patterns of different durations (8, 16, 32 steps) and repeats the shorter pattern matching the length of the longest duration.

• Supports specifying a velocity via Pattern.Beats which is a map of steps to velocity. See example below - where a snare has a velocity of 3 at 13th step, while all other patterns and steps have a default velocity of 1:

    song := NewSong(title, bpm)
    kick := map[int]int{1: 1, 5: 1}
    snare := map[int]int{5: 1, 13: 3}
    hihat := map[int]int{3: 1, 7: 1}
  
    song.AddPattern("Kick", kick, "Kick.aif")
    song.AddPattern("Snare", snare, "Snare.aif")
    song.AddPattern("HiHat", hihat, "HiHat.aif")
  

• I ran out of time implementing outputting the sound. See play.no_go for my attempt, which is just a copy from gordonklaus/portaudio - I got it to play the patterns but they are not in synch with the beat (there is too much lag).

End.