study 05 of 10

Tracks and steps

So far every function worked on “the track”: the current one, the track you were on when you opened the menu. tr.add 5 never says which track, and that is on purpose. Operations act on a context: a set of tracks, a set of steps, and a source of chance. This study changes the context to write a beat on three tracks at once.

Choosing the tracks: `trk`

trk takes one to eight track numbers, or cur (the current track), or all. Like a modifier, it governs the rest of its line or the block below:

Listing 5-1 · Kick, snare and hats on tracks 1, 2 and 3

def beat
  menu "LEARN" >> "BEAT"
  trk 1 2 3: tr.clr
  trk 1: l 1 16: if eq mod i 4 1: tr.add i
  trk 2:
    tr.add 5
    tr.add 13
  trk 3: l 1 16: if er 11 16 i: tr.add i

Output · what the simulator prints for $ otype.py run beat -v

beat  seed 1 (--seed)  pattern A01 len 16 (default)  track 1
T1  1   5   9   13
    X...X...X...X...
T2  1   5   9   13
    ....X.......X...
T3  1   5   9   13
    X.XX.XX.XX.XX.XX
      X trig  ! one-shot  o trigless trig  - trigless lock  l locks only  . none
part:  tempo 120
cost: 520/588   random draws: rand 0  toss 0  prob 0  drunk 0  file 0

With several tracks, OType runs what trk governs once per track, in the order written: trk 1 2 3: tr.clr clears track 1, then 2, then 3. Everything inside a pass, a loop or a random draw, runs again for the next track.

For the rest of the block

trk can also stand alone, without a colon. It then sets the tracks until the end of the block it is in:

Listing 5-2 · trk as a statement

def on_track_2
  menu "LEARN" >> "TRACK 2"
  trk 2                 # from here to the end of the function
  tr.clr
  tr.add 1
  tr.add 9

Either way, a block hands its context back when it ends: after trk 2: and its block, the next line is on the tracks it was on before.

Choosing the steps: `steps` and `step`

The context also holds a set of steps, at first every step of the pattern. steps changes it:

write	the steps become
`steps all`	every step
`steps 9 16`	steps 9 to 16
`steps has.trig`	those of the current steps that hold a trig
`steps is.empty`	those of the current steps that are empty
`step 5`	step 5 alone

A range replaces the steps; a test such as has.trig narrows the ones you already have. Operations that work on many steps at once, and each:, use this set:

Listing 5-3 · Accents on the hats, wherever their trigs fall

def hat_accents
  menu "LEARN" >> "HAT ACCENT"
  trk 3:
    tr.clr
    l 1 16: if er 11 16 i: tr.add i
    steps has.trig:
      each: pl.set i amp.vol dr.v 1 i

Output · what the simulator prints for $ otype.py run hat_accents -v

hat_accents  seed 1 (--seed)  pattern A01 len 16 (default)  track 1
T3  1   5   9   13
    X.XX.XX.XX.XX.XX
    step 1: amp.vol 127   step 3: amp.vol 80   step 4: amp.vol 80   step 6: amp.vol 80
    step 7: amp.vol 80   step 9: amp.vol 127   step 10: amp.vol 80   step 12: amp.vol 80
    step 13: amp.vol 127   step 15: amp.vol 80   step 16: amp.vol 80
      X trig  ! one-shot  o trigless trig  - trigless lock  l locks only  . none
part:  tempo 120
cost: 283/674   random draws: rand 0  toss 0  prob 0  drunk 0  file 0

each: visits the steps that hold a trig, and dr.v 1 i reads curve 1, accents on the beats, at step i.

Locks go where the trigs are

On the Octatrack, a lock belongs to a trig. OType follows the machine: a lock written on an empty step is skipped, and the simulator counts it.

Listing 5-4 · Sixteen locks asked, two written

def two_locks
  menu "LEARN" >> "TWO LOCKS"
  tr.clr
  tr.add 1
  tr.add 9
  l 1 16: pl.set i amp.vol 64

Output · what the simulator prints for $ otype.py run two_locks -v

two_locks  seed 1 (--seed)  pattern A01 len 16 (default)  track 1
T1  1   5   9   13
    X.......X.......
    step 1: amp.vol 64   step 9: amp.vol 64
      X trig  ! one-shot  o trigless trig  - trigless lock  l locks only  . none
part:  tempo 120
cost: 216/216   random draws: rand 0  toss 0  prob 0  drunk 0  file 0
two_locks: 14 skipped, no trig (pl.set line 6 x14)

To lock a step without playing it, first make it a trigless lock: tl.add s.

A function inherits the context

When one of your functions calls another, the called function starts with a copy of the caller's context: the same tracks and steps. Whatever it changes stays inside it. This is what lets the next study write a function once and use it on any track.

What you learned

trk 1 2: · trk cur · trk all: the tracks, one pass per track
trk 2 alone: the tracks until the end of the block
steps a b · steps has.trig · step s: the steps: a range, a test, one step
each:: visit the steps of the context
dr.v c s: a velocity from a ready-made curve
tl.add s: a trigless lock: a step that can hold locks without playing

Try it

Put the snare of beat on track 2 with a single if inside a loop.
Lock a random volume on every trig of tracks 1 to 4 with steps has.trig and rrand 60 127.
Use steps 9 16 to clear only the second half of the bar with tr.clr.