By clicking Peak Search you can determine the peak volume and assess the Peak Level for a numerically correct audio level. The RMS Level, on the other hand, measures the power and can easily be used for judging the subjective perception of loudness.The volume of sound objects can be influenced in a number of ways.
What would you like to do?
Adjusting the volume using a ramp band
Changing the volume of several objects
Adjusting the overall volume of the soundtrack
Find out more about how to deal with volume
Right-click a sound object and select Properties. Use the slider control or enter a value in the numeric field to adjust the volume of the object. The value below the slider specifies the dB by which the volume was changed compared to the original audio file volume.
...See also Using slider controls.
For sound objects, ramp band and nodes form a time-dependent volume control. This allows you to implement any volume progression. ... Info about editing ramp bands.
Select respectively mark the required sound objects and right-click one of the objects. Select Special Functions – Change volume ...
Change the volume using the slider controls and click OK. The volume will be changed for all selected sound objects. ... See also Using slider controls.
By clicking Peak Search you can determine the peak volume and assess the Peak Level for a numerically correct audio level. The RMS Level, on the other hand, measures the power and can easily be used for judging the subjective perception of loudness.
The volume for the mix of all sound objects is called sum volume or level. Adjusting the sum volume effects all objects likewise. This is how it is done:
In the Project Explorer, click on tab 
Audio level. Grab one the small double triangle on the very right and move it. You can do this even while playing back. By double-clicking a triangle the control can be reset to zero dB. The triangles in the audio level display allow you to adjust every output individually. ... See also Sum level.
The peak level is indicated by small markers on the dB scale. Reset them by clicking on the audio level bars with the mouse. The peak level must be no means by above zero dB. ..See also Determining the sound track peak level
...Please see also
Which slider controls have a real time effect on sound?
Tips for volume and audio level
The K-System - Checking volume and dynamics
Separate sum level adjustment.