thanks, I did find it under service parameters config:
Current Service: Cisco MOH Audio Translator
Default MOH Volume Level :
This parameter specifies the default Music on Hold volume, in decibels (DB), that is used when the Cisco MOH Audio Translator service converts audio source files. Changes to this parameter ONLY affect audio files that are processed after the change occurs. The default of -24 decibels represents fairly low volume, and enables conference participants to talk over the music if a conference participant has placed the conference on hold (to answer a ringing call, for example). Note: Changes to this parameter automatically take effect within 60 seconds.
This is a required field.
Default: -24.
Minimum: -48.
Maximum: 0.