Gain/volume for dial-tone from asterisk?


I have a gsmgateway (MV-370) connnected to asterisk via SIP.
All works fine,
but the dial tone from asterisk is vey soft, when dialing the number of final partner.

Is there a possibility to increase the loudness of the dialtone from asterisk ?

This is from extensions.conf (SIP-no. of gsmgateway is 2100):

exten => 2100,1,Answer
exten => 2100,n,Set(TIMEOUT(digit)=3)
exten => 2100,n,Set(TIMEOUT(response)=10)
exten => 2100,DISA(no-password|to_analog_phone)

The loudness of the conversation itself, the dial tone from the gsmgateway etc. is fine.