Hdcd Overview; 16-Bit Encoding; 16-Bit Decoding - Pacific Microsonics HDCD Model Two User Manual

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Model Two HDCD User's Manual

HDCD Overview

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The HDCD (High Definition Compatible Digital ) process utilizes a sophisticated encod-
ing/decoding system that greatly reduces both additive and subtractive distortions in
digital audio recordings, while remaining compatible with all PCM digital formats, includ-
ing Compact Disc and DVD-Audio.
The extraordinary fidelity of the HDCD process is achieved by identifying and correcting
previously misunderstood (or unknown) sources of distortion in digital audio reproduc-
tion. These include both additive artifacts of the analog-to-digital and digital-to analog
conversion and filtering processes that occur with all digital formats, and subtractive
distortions resulting from insufficient data present in the 44.1 kHz, 16-bit sampling of the
Compact Disc format. The HDCD process effectively cancels the additive distortions and
simultaneously provides additional data to reduce the subtractive distortions. The result-
ing recordings rival, in resolution and freedom from distortion, the finest analog master
tapes, and are compatible with consumer digital audio playback formats and equipment.
HDCD process techniques and terminology are defined in the following sections.

16-bit Encoding

Most of the intelligence of the HDCD process has been incorporated in the Model Two HDCD
Processor, lowering the cost to implement HDCD decoding in consumer equipment. An
analog signal fed to the Processor is converted into a digital signal having a 24-bit word
length and a sampling frequency of 176.4 kHz. After decimation to 88.2 kHz, a continuous,
real-time analysis of the signal is made using DSP to determine what elements beyond the
range of conventional 16-bit, 44.1 kHz, formats are perceptually important. The analysis
uses algorithms derived from Pacific Microsonics' research on psychoacoustics and the
mechanisms of auditory perception.
Once the perceptually important high-resolution information is identified, it is encoded
into a Compact Disc standard, 16-bit, 44.1 kHz, linear PCM signal using two methods. Part
of the information is added directly to the 16-bit signal by optimizing utilization of its
linear bits, and part is hidden in the LSB of the 16-bit signal. Over time, less than 5% of
the LSB is used for the hidden code. The encoded information is inaudible and causes no
perceptible loss of information.

16-bit Decoding

When an HDCD encoded signal is fed to conventional playback equipment, the additional
information in the signal is perceived as a clear improvement in fidelity. When the same
signal is fed to an HDCD decoding system, the information hidden in the LSB tells the
system that the signal is HDCD encoded, and directs the decoding to reconstruct the high
P A C I F I C M I C R O S O N I C S I N C .
Rev. C - January 2002
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