Originally Posted by travelfotografer
[These results were from an OPPO-93, but I suspect it may be the same for the OPPO-95 and maybe even the 103/105 models]
I have been testing if the OPPO-93 is bit-perfect as a transport using my Audiolab M-DAC's bit-perfect test.
I burnt the test wav files to a CD-R as CDDA format. If I set OPPO's HDCD Decode to ON and play the disc, the digital output from the OPPO is NOT bit-perfect! If I set OPPO's HDCD Decode to OFF, the digital output from the OPPO is bit-perfect.
For some insight, I have a HDMI->SPDIF box connected to my OPPO-93, and the SPDIF output is connected to the M-DAC. When OPPO's HDCD Decode to ON, regardless if the CD is a regular CD or a HDCD, the digital output from HDMI->SPDIF is 24bits 44.1kHz (as read from the M-DAC display). It is not surprising that this happens on the HDMI output for non-HDCDs (to implement the -6db digitally when HDCD decode is ON), but surprisingly, this seems to affect the regular 16-bits optical/coax digital output of the OPPO too, making the regular optical/coax digital output non bit-perfect when playing non-HDCDs.
So, for those who want to make sure that their OPPO-93 is sending the exact same bits from the CD to the DAC, remember to check and set your HDCD Decode option to OFF!
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.