Page 22 in the Instruction manual. You can make these settings in the CTX or in Universal Settings in XChange2. You can set: Volume Gain, Threshold Level (this is what most people refer to as Volume - how loud the background hum is), Volume Limit, and Threshold Pitch. If doing these settings in the CTX, you have to have the particular listening method activated to adjust the settings for that particular method, ie CTX speaker, wireless module. There are 4 methods of listening, they are shown in the manual. I made my adjustments to the CTX Speaker first. Then turned on the module, and made those settings, then plugged in the phones to the module and made the settings for them. If you need to adjust the settings for phones plugged into the CTX, do that before turning on the wireless module. Once the module is on and shut the CTX speaker off, if you shut off the module you will still have a silent CTX . I just turn it off and back on to restore the Sound to the CTX speaker. Hope I didnt make that too confusing. I forgot to mention how to make the settings. With the listening method you want to adjust settings, hold down the button with the speaker symbol. A menu comes up with the 4 things to adjust. Click on them one at a time and right or left button to increase or decease the setting.