Dolby True HD is one of the two best surround sound formats found in today's Blu-ray-based home theater systems. This lossless surround format is identical to the sound heard at the theater and comes across best via HDMI connection from Blu-ray players.
Dolby TrueHD is a lossless audio format, which means there is no fidelity lost when encoded onto Blu-ray.
The only ways to get Dolby TrueHD with an HDMI connection to a receiver that can decode it, or with a 6-channel analog connection between a BLu-ray player with such outputs and a receiver with a multi-channel input.
The next step down in fidelity with Blu-ray players is Dolby Digital Plus, which is found on some Blu-rays and on some streaming titles from Netflix and some other streaming services.
Other Dolby Resources
Also, look at the other HD audio standard: DTS-HD Master Audio.