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Old 20th January 2013, 21:00   #38  |  Link
MvB
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Join Date: Apr 2002
Location: Between the horns...
Posts: 249
HDCD stores Data in subchannels, too

Hi there,

i always wondered why my backup of Kari Bemnes "Norwegian Moods" sounded much worse when burned from wavs i extracted with eac before from my original disc (HDCD, but not labeled as one). I found out why:
while looking through the internet collecting information about hdcd i found an article from a guy called _Ilya_:

"Data range from -30000 : 30000 is linear. Range above and below is non linear. Multiplier coefficients are recorded in sub-channel (part of audio CD format). Sub channel is not big enough to keep additional 4 bits, but it can keep multiplication coefficient.

In other words HDCD data format is a 2 pieswise interpolation to logarithmic scale. Full range is appropriate to 20 bit. Data precision at any point is 16 bit. (technology similar to voice A-law, M-law compression).

HDCD played on standard CD equipment will distort high levels.
HDCD played on separate transport and processor may be distorted because if sub channel is not transmitted, but processor is HDCD capable, processor will try to apply HDCD decoding because it will find HDCD patterns in upper levels, but without sub channel it does not know how to amplify it. The result is floating level (The same may be achieved if you copy HDCD using NERO but do not copy sub channel).
HDCD can not be saved in .wav because sub channel will be lost. HDCD processor will find patterns in peaks, led will flash."

I thought to myself, that would be an explanation why my copies sound so strange, lifeless.

I made a copy with clonecd, activating "read infos from subchannels" and made an image.

Before burning the image, i set the option "don't correct subchannel streams". Burned with Burning Speed 1x, because the subchannels don't have any crc correction, thought it would be safer that way.

And ... got an epiphany after inserting the fresh burned cd in my hdcd-player: I sounded exactly like the original. Finally. Now i know why. Have to rip my other hdcds again as an image with subchannel information.

Without the subchannel - Information it's quite possible you just get quasi 15 bit resolution in your 20 bit file with no dynamic expansion at all.
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