The S/PDIF (Optical/Coax) outputs are capable of carrying 24-bit stereo LPCM, so why not?
HDCD is 20-bit data encoded as 16-bit data (with the side effect of raising the noise floor a tad). When decoded, the OPPO outputs the 20-bit result packed into 24-bit with padding zeroes.
Are you sure the "bit perfect" test isn't simply complaining that the stream is 24-bit instead of 16-bit? When playing a non-HDCD disc, the 24-bit stream should be a bit perfect representation of the 16-bit original, just packed into 24 bits with padding zeroes.
It may not be a "filter" issue at all, but rather that the "bit perfect" test is being more picky than makes sense.
The Audiolab MDAC shows the true bit-depth of the incoming LPCM. The MDAC designer has repeatedly clarified that if the incoming LPCM is 20-bit result packed into 24-bit with padding zeros, the MDAC display will show 20-bit and not 24-bit. That the M-DAC shows 24-bit indicates that some dithering may be taking place to fill in those extra 4 bits, making all 24 bits "meaningful"
I did not and was not concerned about bit-perfect testing from a 24-bit stream in the case of a CDDA disc (more on that later). I was interested in if the OPPO is bit-perfect as a CDDA transport, i.e. read 16bit/44.1kHz from CDDA and output the exact same 16bit/44.1kHz on the digital outputs. If I set HDCD Decode to OFF, both the regular Optical/Coax digital out AND the HDMI->SPDIF(Coax) passes the bit-perfect test, and in both cases, the M-DAC show the incoming LPCM as 16bit/44.1kHz.
It is only when HDCD Decode is set to ON, the regular Optical/Coax digital out fails the bit-perfect test, while showing 16bit/44.1kHz. With HDCD Decode is set to ON, playing non-HDCD CDDA discs via HDMI->SPDIF(Coax) has the M-DAC show the incoming LPCM as 24bit/44.1kHz.
The MDAC has bit-perfect tests for both 16bit/44.1kHz and 24bit/96kHz. Both files, either burned as WAV or FLAC files on a DVD-Data disc, or streamed from a DLNA server, pass the bit-perfect test via regular Optical/Coax digital out and HDMI->SPDIF(Coax). This shows that the OPPO is bit-perfect most of the time, except when playing non-HDCD CDDA discs with HDCD decode set to ON.
Note that the bit-perfect test files are not HDCD encoded. This is not a test about if the OPPO is bit-perfect when playing back HDCD-encoded CDDA discs.
Edited by travelfotografer - 11/30/12 at 10:00am