The HD Advisor Number 23

High Def Digest takes in some reader questions on some high definition types of questions. Their first answer covers the differences between PCM and the lossless compression formats, a topic which I have heard many times since they were released. Since HDMI 1.3 is currently a big pain on the PC, it’s been a difficult time to educate people on just what is going on…and that NOT having the bright blue Dolby light on your receiver isn’t necessarily a bad thing.

High Def Digest

Dolby TrueHD and DTS-HD Master Audio are just compression codecs, lossless in both cases. They function like a ZIP file. You take the space-hogging source data (the PCM), ZIP it, and press the resulting file onto the disc with considerable storage savings. Upon playback, the file must be decoded, which is akin to unZIPing it. Because the codecs are lossless, the extracted results will be 100% identical to the original PCM. The decoding process can be done either in the Blu-ray player (if it offers that function) or in the A/V receiver. In either case, the basic steps are the same. You start with TrueHD or Master Audio. That’s decoded to PCM. The PCM is converted to analog, and then the analog signal is amplified out to your speakers. The only difference is where each of these steps takes place.