Builtin Variables

A few identifiers in Akkado are not ordinary variables — they are builtin variables, backed directly by the synth engine’s runtime state. You read them like any other name, and one of them (bpm) you can also assign.

Name	Access	Default	Meaning
bpm	read-write	120	Project tempo in beats per minute (1–999)
sr	read-only	48000	Audio sample rate in Hz
spb	read-only	0.5	Seconds per beat — equals 60 / bpm

Reading a builtin variable

Reading bpm, sr, or spb gives you a live value. The read tracks the running engine, so when you move the Transport’s BPM control the value updates without recompiling:

// A delay locked to one beat — follows the Transport tempo live
saw(220)
    |> delay(@, spb, 0.5)
    |> out(@)

spb is the convenient primitive for tempo-relative timing. Use it wherever a duration should scale with tempo:

dotted8 = spb * 0.75   // dotted-eighth note in seconds
quarter = spb          // one beat

sr is useful when a calculation needs the sample rate:

nyquist = sr / 2

Setting the tempo

Assigning bpm sets the project tempo. The value is extracted at compile time and applied to the Transport, so the BPM control in the UI updates to match:

bpm = 140

The right-hand side must be a compile-time constant. Arithmetic on constants is fine; runtime controls are not:

bpm = 60 * 2              // OK — evaluates to 120
bpm = param("t", 120)     // Error — not a constant

Values are clamped to the valid range 1–999. Multiple bpm = lines are allowed; the last one wins.

Rules

• sr and spb are read-only — assigning them is a compile error.
• bpm must be assigned a constant; a non-constant or non-numeric right-hand side is rejected.
• A builtin variable cannot be declared const (const bpm = 120 is an error) — its read/write behavior is fixed by the language.