MRC01
Major Contributor
- Thread Starter
- #21
I found an example among my CD collection so I'll share it here. It is Reference Recordings RR-79, Pictures at an Exhibition, starting on track 9. I played on my Oppo BDP-83, whose settings permit enabling or disabling HDCD encoding, and captured the digital output on a Tascam recorder at recording level "max" so it wouldn't change the bits. The recorded non-decoded bitstream shows as "HDCD enabled", so the Tascam made bit-perfect copies.
I'll cut to the chase with some before/after pictures, hopefully worth 1,000 words:
First, the non-decoded waveform - what you get without an HDCD player. It still rates a decent DR15.
Next, the decoded waveform, which rates DR19.
In both cases (with and without HDCD decoding), peak levels are a smidge below 0 dB. With HDCD disabled, the quiet/average levels are 6 dB louder and the dynamic peaks are softly compressed. With HDCD enabled, it shifts the quiet parts / average levels down 6 dB quieter which makes room for the expanded dynamic peaks. Another way to put this: when you enable HDCD encoding in settings, it plays much quieter.
With quiet parts shifted 6 dB (1 bit) lower, HDCD seems to trade resolution in quiet parts for bigger dynamic range. That is, shifting the quiet parts down by 6 dB means they have 1 bit less resolution, in order to make the dynamic peaks 1 bit louder. Perhaps the low level extension feature was intended to fix that and restore resolution in the quiet parts. Or, perhaps the DAC was supposed to do all of this in 20 or 24-bit so it doesn't lose resolution when it shifts the quiet parts down.
Note: The BDP-83 decodes HDCD on both analog & digital outputs. But my DAC says the digital outputs are still 16-bit even when HDCD is decoded. Looks like Oppo realized (or assumed) that none of the HDCD discs actually use more than 16 bits of dynamic range, so they didn't use 24-bit output. This player does emit 24-bit data for DVD-A, so the 16-bit output for decoded HDCD seems like a software choice rather than a hardware limitation.
I'll cut to the chase with some before/after pictures, hopefully worth 1,000 words:
First, the non-decoded waveform - what you get without an HDCD player. It still rates a decent DR15.
Next, the decoded waveform, which rates DR19.
In both cases (with and without HDCD decoding), peak levels are a smidge below 0 dB. With HDCD disabled, the quiet/average levels are 6 dB louder and the dynamic peaks are softly compressed. With HDCD enabled, it shifts the quiet parts / average levels down 6 dB quieter which makes room for the expanded dynamic peaks. Another way to put this: when you enable HDCD encoding in settings, it plays much quieter.
With quiet parts shifted 6 dB (1 bit) lower, HDCD seems to trade resolution in quiet parts for bigger dynamic range. That is, shifting the quiet parts down by 6 dB means they have 1 bit less resolution, in order to make the dynamic peaks 1 bit louder. Perhaps the low level extension feature was intended to fix that and restore resolution in the quiet parts. Or, perhaps the DAC was supposed to do all of this in 20 or 24-bit so it doesn't lose resolution when it shifts the quiet parts down.
Note: The BDP-83 decodes HDCD on both analog & digital outputs. But my DAC says the digital outputs are still 16-bit even when HDCD is decoded. Looks like Oppo realized (or assumed) that none of the HDCD discs actually use more than 16 bits of dynamic range, so they didn't use 24-bit output. This player does emit 24-bit data for DVD-A, so the 16-bit output for decoded HDCD seems like a software choice rather than a hardware limitation.