Quote:
Originally posted by C1C2
First thanks for this fast answer to you both!
I now know, as I asked in dchlb, too, there must be two different kinds of PRE-CDs. Some, mainly the "newer" ones show that PRE-flag in the TOC, and as I understand it, if EAC detects it in the TOC, it will copy them, right?
OK, I just found someone, who tested, that EAC won´t recognize, if a CD contains Pre just in the subchannel. If I copy such a CD, it won´t work. So, wouldn´t it be a nice Feature, if EAC could recognize this and correct the TOC-Info automatically?
Thanks again
Philipp
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Hi,
There is only one type of pre-emphasis used in audio CDs, this has been in the standard since day1. The system uses (Used? - perhaps now uses digital filters?) analog filters to change the power spectral density of the recorded material and then relies on the player to use complimentary analog filters to return the signal to the correct 'balance'. The recording filter is a simple shelf filter with rollover points at about 3 and 10 kHz. Its purpose was to decrease the quantisation error in the high frequencies by taking advantage of the natural reduction in signal level at these higher frequencies and thus boosting the higher frequencies.
The player will engage the circuit based on a flag in the Q channel of the subchannel stream for each track. Specifically, it looks for the flag in the control bits of the Q channel frame header which appear in every Q channel frame.
There is no pre-emphasis information in the TOC. The TOC itself is actually contained in the Q subchannel information, specifically in Mode1 during leadin only. Mode 2 and 3 of the Q subchannel contain the ISRC and catalog info and are only used in the program area of the disc (ie not the leadin or leadout). The ISRC changes for each track whereas the catalog is the same for the whole CD.
I assume that EAC gathers all this Q channel information from each track of the CD when it is first analysing it and combines it with the information contained in the TOC to generate the Cue sheet. Certainly you can hear it skipping to each track when it is reading the ISRC info.
So, I am not sure what it was that that person was testing. Perhaps, people were mistakenly believing that all the information in the Cue comes from the TOC.
In any case, pre-emphasised CDs are reasonably rare and almost always classical in content. Of course they will sound rather strange if the .wav is played back without de emphasis, so perhaps the rarity is a good thing.
Regards,
Bob