Microsoft Skype for Business detects your computer’s built-in audio devices and any compatible audio devices that are connected to your computer, such as a headset, a microphone, or speakers. While you are offline, there are some limited audio options you can set. To make test calls and set additional options, you’ll need to be connected.
To open Audio Device options, click Options 
Select an audio device
You can change the audio device that you use for your Skype for Business calls.
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In Audio Device options, in the Select the device you want to use for audio calls list, select the audio device you want to use.
For best results, select the same device for both the speaker and microphone. Choosing separate devices might cause audio echoing during a call. However, if you cannot avoid using separate devices and you experience echoing, you can minimize echoing by lowering the volume of both the microphone and the speaker
Adjust the volume
Here’s how to reset the speaker, microphone, and ringer volume for any compatible audio devices that are built into your computer or connected to your computer:
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In Audio Device options, under Customize your device, drag the handle for the appropriate slider.
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(Optional) Do any of the following:
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To hear a sample tone for the speaker and ringer, click the green arrow next to these sliders.
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To adjust and test your microphone, speak into the handset, headset, or phone you’re using. If the volume of your computer microphone is optimal, the status bar will fill to the middle portion of the test area.
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Troubleshooting
Having problems? See Troubleshoot Lync Audio
