Is it the transport or DAC that enables HDCD/Red?

Add the Esoteric P-70 and I believe the D-05 to the list of DACs that support HDCD. The Classe SACD-1, SACD-2, and several Cary players also support it.

Kijanski - there's much more going on with HDCD than dynamic range switching. The recording is made at 88.2 khz/18 bits. It is then analyzed by the HDCD encoder which decimates the signal to 44.1 khz and applies on a moment by moment basis the selection from a suite of encode processes (compression, filtering,etc) that best preserves the characteristics of the original signal. The encoder also modulates the low order bit to tell the decoder which inverse process to apply at any moment. The result is a 44.1 khz/16 bit data stream that can be played by any CD playback system.

On playback the HDCD decoder reads the low order bit modulation pattern and applies the appropriate inverse process on a moment by moment basis to create 44.1 khz/18 bit data stream from the 16 bit data stream off the disk.

One other important feature - the filter in the decoder is a perfect conjugate of the filter used in the encoder, which by itself improves fidelity.

The intent was to do most of the number crunching on the encode side while the decoder remained simple.

The only responsibility the transport has is to provide an exact copy of the bitstream encoded on the CD (another argument against those who whine about CD data errors - none of this would work without perfect recovery)

Look up other threads on this.

Kinjanki:
Actually the HDCD process has improved since I last looked at it years ago, and my memory was wrong - it produces a 20, not 18 bit datastream. Again it is much more than a simple dynamic range switch. See:

http://mixonline.com/mag/audio_pacific_microsonics_hdcd/

Kijanki: Sigh..., of course dynamic processing is part of the picture, but you left out much of the article and only picked out the paragraph that seemed to support your statements.

For the rest of the story:

"Dynamic-decimation filtering is HDCD's response to the well-known problems inherent in filter design for digital conversion systems where the Nyquist frequency is only slightly above the range of human hearing. "A filter designer who has to make a 'brick wall' filter at 22 kHz is confronted with conflicting requirements," Ritter explains. "You want to have flat frequency response out to at least 20 kHz, but you can't have any energy above 22 kHz or you will get alias distortion. This requires a very sharp multipole filter with a very steep transition between the passband and the stopband, which has a number of distortive effects on the signal. It smears transients and causes significant ripples in the passband. If you try to simplify the filter, then to avoid totally unacceptable aliasing you have to start rolling off at 13 to 15 kHz, and even then the signal will not be completely cut off by 22 kHz."

Ritter describes the HDCD approach to this problem: "We slightly delay the 88.2kHz signal, not enough to cause any sync problems but enough that we can do a continuous Fast Fourier Transform. The resultant information is digitally analyzed in real time by an algorithm that determines, based upon a model of the mechanics of hearing and psychoacoustics, what is perceptually dominant in the signal from instant to instant. And that information is used to optimize the decimation filter. One moment you might have a sudden sharp transient, so it uses a filter with minimum time dispersion to pass the transient cleanly. The next instant, there might be a cymbal crash, so it uses a filter that minimizes alias distortion. All the filters are the same length, so you are not getting a phase shift as this is going on."

Another element in the process of downconverting for CD is word-length reduction to 16 bits. "We never simply truncate," Ritter says. "And with the introduction of Version 2.0 of the Model One at the end of 1998, available as a flash-ROM upgrade to existing units, we now have a palette of four 16-bit dither options." The dither and the dynamic decimation together, Ritter believes, add up to a big improvement over typical CD sound. "The reduced distortion-sharper transient response and reduced aliasing-becomes part of the digital recording and will be heard on any player, whether it has HDCD decoding or not," he says. Nonetheless, the optimal playback setting is one in which the playback filters are matched to those used in recording. To achieve this, the Model One hides control information in the signal that tells the HDCD decoder which filter to use. This data is encoded as a pattern in the dither used for word-length reduction. It occurs only 1% to 2% of the time, and the company says that extensive testing has shown that it is inaudible."

Note that all this processing takes place on the encode side.