Lenovo Thinkpad T410 audio through displayport

Getting audio to pass through to TV when using displayport to HDMI cable

DisplayPort is actually capable of tranmitting audio and video. However some manufacturers or OEMs do not implement the audio pass through, luckily Lenovo has implemented this correctly in their Thinkpad T410.

Follow the step to get your laptop audio to TV.

1. Start playing the video.
2. When video is playing, go to Control Panel -->Sounds-->Playback tab
3. You'll see a list of audio playback devices and TV (or amplifier if you are using one) should be one of the options. 
4. Just choose TV and set it as the default audio device 
5. The audio will be passed automatically to the TV from now on.

AC3filter Dolby AC3 passthrough

If you're sending AC3Filter's output to a surround sound equipped home theater receiver you only need to set the Output Format to AS IS (No Change) and PCM 16bit (for standard Dolby Digital or DTS) and check the Use SPDIF checkbox. This will bypass AC3Filter's internal processing and send the original signal through your S/PDIF connection.

More details here.