In a word, proprietary. The recording studios had to lease or buy the encoder from Pacific Microsonics. Even worse, the builders of playback equipment had to use a Pacific Microsonics oversampling filter chip (PMD-100 later replaced by the PMD-200). This was not compatible with the design strategies of companies like Wadia, Theta, Krell, and others that specialized in custom digital filters implemented on DSP chips.
PM once talked of licensing the algorithms, but to my knowledge this didn't happen. Part of the argument against licensing was that the decoding processing involved a reconstruction filter that was a perfect conjugate to the filter used in the encoder. By implementing the process in a chip PM had complete control of the decoding implementation.
The purchase of PM by Microsoft just made things worse.
I read once that Wadia had a protoype digital processor designed to sit between the transport and DAC. It would decode HDCD and output 20 bit 44.1 khz PCM (this is what the PMD filer chips do) to the DAC. They couldn't market it or build it into a DAC due to licensing issues.
PM once talked of licensing the algorithms, but to my knowledge this didn't happen. Part of the argument against licensing was that the decoding processing involved a reconstruction filter that was a perfect conjugate to the filter used in the encoder. By implementing the process in a chip PM had complete control of the decoding implementation.
The purchase of PM by Microsoft just made things worse.
I read once that Wadia had a protoype digital processor designed to sit between the transport and DAC. It would decode HDCD and output 20 bit 44.1 khz PCM (this is what the PMD filer chips do) to the DAC. They couldn't market it or build it into a DAC due to licensing issues.