The following article details how to disable the digital signal processing (DSP) feature on your Discovery 655/665 headset.
In order to disable the digital signal processing feature, you'll want to enable power saving mode. Power saving mode temporarily disables the Digital Signal Processing (DSP) feature of the Discovery 655 and 665 headsets to provide a longer talk time.
To enable power saving mode, press both the volume up and down keys at the same time before you make a call. To re-enable DSP, press both the volume up and down keys at the same time. Power saving mode cannot be turned on while engaged in a call.
NOTE After you turn off the headset, DSP will be re-enabled the next time you turn it on.