In simple terms, how does the HDCD Decoder operate with the HDCD code data?
The HDCD Decoder examines the LSB of the audio data for each channel and determines if there is the HDCD hidden code present. If so, it resets the code detect timers for each channel and decodes the commands. An HDCD code detect signal is made valid, thus identifying the audio as having been encoded with the HDCD process. Following code extraction, those parameters that affect dynamic range are restored. This includes the expansion of the instantaneous soft limiting peak levels (PE) performed by the encoder if that option was enabled and expansion of the low level gain compression(LLE) based on average signal levels. These exactly complementary gain command instructions are timed to the audio signal so that gain changes are transparent. After the dynamic range of the audio signal has been restored, the HDCD Decoder then performs gain scaling and filter selection. The final step in the decode process involves interpolating the audio signal to twice the sampling frequency using a filter
