Why must the HDCD Decoder have either Digital or Analog Gain Scaling implemented?
One of the very powerful features of the HDCD process is called Peak Extend. Simply put, Peak Extend increases the effective dynamic range of the HDCD encoded material during playback. It allows for an extra 6dB of peak signal amplitude above the standard 0dB full scale normally available. The top 3dB (-3dBfs to 0dBfs) of Peak Extended HDCD recordings contain 9dB of compressed signal level that is uncompressed when decoded. In order to produce this increased dynamic range and because the peak digital signal level prior to decoding is 0dBfs (which cannot increase beyond 0dBfs in the digital domain by definition), the average signal level of decoded Peak Extended recordings must be decreased by 6dB. Since human perception of loudness is determined by average levels and not peak levels, decoded Peak Extended recordings will thus sound 6dB quieter than non-Peak Extended recordings, unless the difference in average levels is compensated for after the decoding has been performed. Digital (or
