An ISoundTypeDefinition object represents a sound (type) in the game. A sound type is almost always bound to one or multiple blocks.

It might be required for you to import the package if you encounter any issues, so better be safe than sorry and add the import.
import mods.contenttweaker.SoundType;

You can get such an object using the Sound Type Bracket Handler:
<soundtype:wood>

ZenMethod	Return type	Definition
ZenMethod getVolume()	Return type float	Definition Returns the type's volume
ZenMethod getPitch()	Return type float	Definition Returns the type's pitch
ZenMethod getBreakSound()	Return type ISoundEventDefinition	Definition Returns the sound that occurs when the related block is broken
ZenMethod getStepSound()	Return type ISoundEventDefinition	Definition Returns the sound that occurs when the related block is stepped on
ZenMethod getPlaceSound()	Return type ISoundEventDefinition	Definition Returns the sound that occurs when the related block is placed
ZenMethod getHitSound()	Return type ISoundEventDefinition	Definition Returns the sound that occurs when the related block is hit
ZenMethod getFallSound()	Return type ISoundEventDefinition	Definition Returns the sound that occurs when the related block is falling