NB! It seems this console command is not compatible with CS2.
Command Profile

VOICE_CASTER_SCALE

CS:GO

This command sets the volume of the GOTV caster. Default is 1, lower numbers (decimal) are quieter. 0 is off.

Syntax
voice_caster_scale [0 - 1]

Description

This command sets the volume of the GOTV caster. Default is 1, lower numbers (decimal) are quieter. 0 is off.

Syntax And Arguments

voice_caster_scale [0 - 1]
0 - 1 A number between 0 and 1 to represent the scale of the caster's voice. 1 being loudest and 0 being muted. 0.5 would be 50% volume.