Sound Blocks in Scratch

Sound blocks are color-coded pink, and are used to control sound and MIDI functions.

There are currently 13 Sound blocks: 11 Stack blocks and 2 Reporter blocks.

 

NameBlockFunction
Play SoundThe block will play the specified sound, with no pause to its script
Play Sound until DoneThe block will play the specified sound, pausing its script until the sound has finished playing
Stop all SoundsThe block will stop any sounds currently being played on all sprites and the Stage. Pressing the Stop button will also stop all sounds, but is rarely used as it also stops all the other scripts running in the project.
Play DrumThe block will play the specified instrument for the specified amount of seconds using a MIDI drumset. Even though the block uses the word "drum", the choices in the drop-down menu are many different percussion instruments including drums, triangle, bongos, cowbell, vibraslap, and various idiophones.
RestThe block pauses its script for the specified amount of beats, which can be a decimal number.
Play Note

The block will play the specified note with a set MIDI instrument for the specified amount of beats.
Set Instruments

The block changes the set MIDI instrument that the Play Note () for () Beats block will play.

Change VolumeThe block changes the volume of a sprite by the specified amount.
Set VolumeThe block sets its sprite's volume to the specified amount. It only affects the sprite (or the Stage) that the block is in.
Change Tempo

The block changes the project's tempo by the specified amount.
Set TempoThe block sets the Scratch project's tempo, or speed, to the specified amount
VolumeThe block holds a sprite's or the Stage's volume. This block can be displayed as a Stage monitor.
TempoThe block holds the Scratch project's tempo. This block can be displayed as a Stage monitor.

The above information is referenced from Scratch Wiki.