Exercise 16: A blast you can hear

Purpose. To give the explosion a sound that is fired with it and comes from its place in the world. The sound should never play exactly the same way twice.

A sound belongs to an effect as much as its sparks do. It must start at the same instant, come from the same spot, and vary from one blast to the next. A Sound can be transformed like anything else, and then it is fired, timed and layered with the rest.

Before starting

• The Explosion folder from Exercise 15 is in the workspace.
• One new ordinary Part named Boom is inside the folder, at the centre of the explosion, anchored, with Transparency 1 and CanCollide off.
• Inside Boom is one Sound named Blast, with its SoundId set to an explosion sound.

Procedure

Steps 1, 2 and 6 repeat earlier exercises on a new kind of emitter.

Step	Control	Action	Result
1	Blast	Select, then press Transform	The Properties panel shows the sections of a Sound emitter, with Emission and Sound open. The Emit box reads 1.
2	HUD ▸ Emit button	Press	The sound plays once, from the place where Boom is.
3	Properties ▸ Sound ▸ Speed	Enter 0.9, 1.15	No change yet.
4	HUD ▸ Emit button	Press several times	Each play has a slightly different pitch.
5	Properties ▸ Sound ▸ Roll-off Max	Enter 150	The sound is no longer heard from more than 150 studs away.
6	Explosion	Select, then press Emit on the HUD	Fire, smoke, flash, jolt, shockwave and sound go off together.

CAUTION

With Enabled on, a Sound emitter starts a new play at its Rate, and the plays overlap. At Rate 10 that is ten plays a second on top of one another. For one sound, use the Emit box with a count of 1.

CAUTION

Give a looped sound a Lifetime above 0. With Looped on and Lifetime at 0, the sound keeps playing for up to an hour, or until the emitter is stopped.

What the steps did

A Sound emitter plays a duplicate of the Sound each time it is fired. Transform keeps the Sound’s volume, speed, roll-off distances and Looped setting. It starts with an Emit count of 1.

The sound comes from the Part or Attachment that holds the original Sound, and follows it if it moves. A Sound emitter nested in another emitter plays from each parent particle and travels with it.

Row	Starts at	What it sets
Emission ▸ Lifetime	0	How long each play lasts, in seconds. At 0 the sound plays once to its end. Above 0 the play is cut off at that time.
Emission ▸ Start At	0	How many seconds into the clip the play begins.
Emission ▸ Looped	The Sound’s own setting	The clip repeats until the Lifetime ends.
Emission ▸ 2D (local)	Off	On, the sound has no place in the world. It is heard at the same volume everywhere.
Sound ▸ Volume	The Sound’s own volume	The volume, over the life of the play.
Sound ▸ Speed	The Sound’s own speed	The playback speed, which is also the pitch, over the life of the play.
Sound ▸ Roll-off Min	The Sound’s own distance	The distance, in studs, at which the volume begins to fall.
Sound ▸ Roll-off Max	The Sound’s own distance	The distance, in studs, beyond which the sound is not heard.

Volume and Speed are graph rows. Two numbers typed into either one give each play a value of its own between them, as with Speed in Exercise 1. A drawn graph changes the value while the sound plays.

If the result differs

Symptom	Cause	Action
No sound at step 2	The Sound has no SoundId, or Studio’s own volume is off.	Set the SoundId on the RenderTemplate inside Blast, which is the duplicate that is played.
The sound is equally loud everywhere	2D (local) is on, or the Sound is not inside a Part or an Attachment.	Switch 2D (local) off. Keep the Sound inside Boom.
The sound is cut short	Lifetime is above 0 and shorter than the clip.	Enter 0 for Lifetime.
Many sounds pile up	Enabled is on.	Switch it off and use the Emit box.
The sound does not fire with the rest	Boom is not inside Explosion.	Drag it into the folder.

Variations

Change	Result
Sound ▸ Volume 0.4, 0.6	Each blast is a little louder or quieter than the last.
Sound ▸ Volume, a graph that falls to 0	The sound fades out as it plays.
HUD ▸ Delay 0.1 on Blast	The sound arrives a moment after the flash, as from a distant blast.
A Sound emitter inside the RenderTemplate of the rocket of Exercise 9	Each rocket carries its own whoosh, which stops when the rocket ends.
Looped on, Lifetime 3, a Speed graph from 0.6 to 1.4	A hum that rises in pitch for three seconds.
Emission ▸ 2D (local) on	A sound for a menu or a screen effect, heard at full volume wherever the camera is.

Log

New in this exercise	Transforming a Sound. Speed as pitch. Roll-off Max. Lifetime 0.
Done before	Transform (eight times). The Emit button (nine times). Two numbers in a graph row (Exercise 1). A Folder fired as one (Exercises 10, 11 and 15).
Carried forward	Keep Explosion. The next two exercises fire it from a script.