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Check for full duplex capability

How to find out if hardware supports full duplex record and playback.


Check for full duplex capability
Tom Lancaster

If you're planning to roll out VoIP in your network in the future, make sure to verify that the audio hardware in your desktops supports full duplex. Full duplex audio means that you can record and playback at the same time, and this is obviously a very important feature for VoIP, because without it, you would only be able to speak or listen, but not both at the same time! Unfortunately, many PCs have hardware that does not support full duplex audio, and in these cases, you'll likely have to use an external device, like an IP phone instead of your PC's sound card and microphone. Having to upgrade sound cards in a few PCs in a small office may be pretty annoying, but it can be a budget-buster if you order 200 soft-phones for your corporation and find out your desktops will all require upgrades before you can use them.

Checking to see if your desktops support full duplex audio is fairly simple. Start by making sure your microphone and speakers are plugged in and turned on. Open a program that you can use to record and playback sound from your microphone. Microsoft's Sound Recorder is a free package that ships with Windows (Start/Programs/Accessories/Entertainment/Sound Recorder). If you don't already have a favorite 3rd party application, use the Microsoft app.

Next, make a recording. Do this by clicking the "record" icon (the red ball on the far-right pushbutton) and speaking into your microphone for at least one minute. After you have finished, open a second instance of Sound Recorder (or your favorite application). On the first Sound Recorder, rewind your recording and play it back. Once it starts to playback, quickly switch to the 2nd instance of Sound Recorder. On the 2nd instance, begin recording again for a few seconds.

If you can playback the 2nd recording, then you know your hardware supports full duplex audio.

Thomas Alexander Lancaster IV is a consultant and author with over ten years experience in the networking industry, focused on Internet infrastructure.

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