ENVELOPE CREATE n,wave,volume,pulse_width,attack,decay,sustain,release,vibrato_depth,vibrato_rate,glide,pwm_rate,pwm_depth

ENVELOPE DESTROY n

Defines or removes a stored sound envelope.

An envelope describes how a generated tone evolves over time — its loudness, pitch, and timbre changes. This allows Retro Rocket to act like a very simple synthesiser, much like the BBC Micro’s classic sound system, but with added flexibility.

CREATE

Creates or replaces an envelope in slot n (0–63). The envelope can then be used by SOUND TONE to shape generated notes.

Parameters:

n — Envelope index (0–63). A slot number that lets you store multiple different sound shapes and pick between them.
wave — Base waveform type: the raw “tone colour.”
- 0 = square — harsh and “beepy,” like an old 8-bit computer.
- 1 = sine — smooth and pure, like a flute.
- 2 = sawtooth — bright and buzzy, common in synth leads.
- 3 = triangle — softer, hollow-sounding.
- 4 = noise — random hiss, used for percussion and effects.
volume — Base loudness (0–255). Higher numbers = louder.
pulse_width — For square waves only: controls how long the “on” part of the wave lasts in each cycle.
- 128 = 50% duty cycle = classic square.
- Lower values = thinner, “nasal” sound.
- Ignored for other waveforms.
attack — How fast the sound rises from silence to full volume when a note starts.
- Short attack = instant click or pluck.
- Long attack = gradual swell.
decay — After the peak, how quickly the sound drops down to the sustain level.
- Short decay = sharp, percussive.
- Long decay = smoother, fading into sustain.
sustain — The level (0–255) held while the key/note is pressed.
- High sustain = sound keeps strong.
- Low sustain = sound fades to a faint background.
release — How long the note takes to fade back to silence after it ends.
- Short release = abrupt cut-off.
- Long release = lingering echo.
vibrato_depth — How far the pitch wobbles up and down.
- Measured in cents (100 = one semitone).
- Small depth = gentle shimmer; large = dramatic warble.
vibrato_rate — How fast the vibrato wobble happens (Hz = cycles per second).
glide — Portamento: how long it takes to slide from one note’s pitch to the next.
- Short glide = nearly instant jump.
- Long glide = smooth slide between notes.
pwm_rate — Speed of pulse-width modulation (Hz). Only affects square waves. Creates a “chorus-like” movement.
pwm_depth — How much the pulse width is swept back and forth (0–255).
- Small depth = subtle shimmer.
- Large depth = dramatic, hollow sweep.

Together, these controls let you create sounds ranging from short plucks to smooth pads, or classic “SID-style” chiptune effects.

Visual example

The blue line shows the amplitude (the technical term for volume, the height of the waveform) of the sound over time, with time being the X axis the Y being the volume (amplitude)

DESTROY

Removes an envelope from slot n (0–63), freeing it for reuse.

Example

' Envelope 0: simple organ tone
ENVELOPE CREATE 0,0,255,128,5,50,200,200,0,0,0,0,0
 
' Envelope 1: slow sine pad
ENVELOPE CREATE 1,1,200,0,500,300,180,800,0,0,0,0,0
 
' Play notes with the defined envelopes
STREAM CREATE s
SOUND TONE s,440,100,0   ' A4 with organ
SOUND TONE s,220,200,1   ' A3 with sine pad

Notes

Envelopes are stored in slots, numbered 0–63. Each BASIC program has its own 63 slots.
Each SOUND TONE` may optionally use an envelope, or omit te envelope number to play a raw, simple square wave.
Unlike sampled sounds (SOUND LOAD, SOUND PLAY), tones are generated on the fly and do not consume memory.
You can create expressive, evolving sounds by experimenting with different waveforms and envelope timings.