How to configure adb environment variable

in win7 system I. Hardware problem
This situation should be ruled out first, regardless of whether you are using a speaker or a headset, please check if the device is properly connected to the computer and try to re-plug the audio cable.
Second, the system setup problem
This situation is very complicated, there are many possible reasons, let us look at the general solution steps.
Set the sound related properties
1. First enter the control panel —— sound options, there should be a device like a speaker under the play tab, double click to open the properties window, in the level tab, to keep The speaker-like button is in a normal state;
2. Similarly, if the microphone has no sound, enter the level column in the recording tab and keep the sound-like icon in a normal state.
Third, check if there is a problem with the sound card driver
Right-click the computer option in the Start menu, select Properties, go to the Device Manager, and see if there are yellow or red exclamation marks in the sound, video and game controllers. If you have any, please try to update the sound card driver (downloadable driver wizard automatically updated).
Fourth, check whether the Win7 sound service is disabled
Right-click on the computer item in the Start menu, select Manage, enter the service options, find the Windows Audio item to ensure it remains enabled.