Thread: Pre-emphasis and use in EAC

Hi,

I´m a bit confused about this and how EAC handles it.

If I put in a CD, EAC shows, if there ist pre-emphasis used.
As I just got to know these information seem to be written only inside the subchannel-information.

Are they copied, if I use "create image and cue-sheet"?
What information about this is stored in the TOC of the original and the copy?

How ist this handled by a CD-Player?

Thanks in advance
Philipp

No, you have to use a WAV editor to do deempasisation... Anyway this is not needed if you want to write it on CD, there is a "FLAGS PRE" in the CUE sheet for that...

cu, Andre

De-Emphasis is carried out by the CD player if the appropriate flag is set ... EAC will copy this flag so you don't need to worry about that

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

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

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

The TOC data length indicates the length in bytes of the following TOC data. The TOC data length value does
not include the TOC data length field itself. This value is not modified when the allocation length is insufficient
to return all of the TOC data available.
The First Track Number field indicates the first track number in the first complete session Table of Contents.
The Last Track Number field indicates the last track number in the last complete session Table of Contents
before the Lead-out.
The ADR field gives the type of information encoded in the Q Sub-channel of the block where this TOC entry
was found. The possible ADR values are defined in Table 294.
The Control Field indicates the attributes, of the track, see Table 295.
The Track Number field indicates the track number for that the data in the TOC track descriptor is valid. A
track number of AAh indicates that the track descriptor is for the start of the Lead-out area.
The Logical Block Address contains the address of the first block with user information for that track number
as read from the Table of Contents. An MSF bit of zero indicates that the Logical Block Address field contains
a logical block address. An MSF bit of one indicates the Logical Block Address field contains an MSF address
(see sub-clause 4.1.6).

So, the information whether a track has pre-emphasis or not is also stored in the TOC (in the control field is the information whether the sector is pre-emphasised or not).

So I think it is an "illegal" TOC when a track needs deamphasising, but it isn't entered in the TOC (of course, for most players this really doesn't matter)...

Anyway, if you know that a track is pre-emphasis, just add in the CUE Sheet FLAGS PRE
I also don't know if "Detect TOC manually" would work out pre-emphasis... Test it!

cu, Andre

If I want to burn tracks with pre-emphasis as Audio later, there's no problem with EAC because it respects the PRE flag from the cue-sheet during burning (Nero doesn't!!!).

But what if I want to create a compressed format for use in a player capable playing back that compressed format (e.g. mp3 players). Because the mp3 file itself doesn't know about the PRE flag the result is a totally wrong frequency curve!

Andre wrote:

No, you have to use a WAV editor to do deempasisation

I just tried to find a WAV-Editor who can handle deephasation and wasn't lucky. Do you know a WAV editor which is capable of doing the job correctly? (I normally used cool edit but it doesn't have this function!)

Found on the internet :

2. Instead of re-flagging, apply software de-emphasis to the pre-emphasised
wav file on your HD. Use a wave editor such as CEP/SF/Wavelab equipped with
the Waves Direct X plugin - Waves Q 10 Paragraphic software preset "DAT-CD
de/pre-emphasis". That has served me well for re-balancing some old PCM 601
tapes.

3. If you don't have this plugin then you can get always get an
approximation to the de-emphasis curve using a graphic or multiband
parametric equalizer.
If it is any help, you can generate your target 15/50us EIAJ de-emphasis
curve using the following equation:
============================================================
y = 10log(A/B) - 10.4576

where:

y = dB output at a frequency of f Hz
A = 1 + 1/(H x H)
B = 1 + 1/(L x L)
H = (2 x pi x f x t(H))
L = (2 x pi x f x t(L))
t(H) = high freq. time-const (0.000015 sec)
t(L) = low freq. time-const (0.000050 sec)
10.4576 just normalizes the response relative to 0 Hz = 0dB

(make the dB figures all pos. or all neg. for pre- or de-emphasis, resp.).
===========================================================

Hope this helps....oh, and I'm pleased with Cool Edit Pro at its slowest
setting for 48->44.1 resampling.

cu, Andre

One more (for using graphical EQ) :

then you will likely lose the flags and your DAT tape will sound too bright.
How bright? The 15/50us pre-emphasis boosts as follows:
================================================================
kHz 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
dB 0.0 0.0 0.0 0.1 0.1 0.1 0.2 0.2 0.3
================================================================
kHz 1 2 3 4 5 6 7 8 9 10
dB 0.4 1.3 2.4 3.5 4.5 5.4 6.1 6.7 7.2 7.6
================================================================
kHz 11 12 13 14 15 16 17 18 19 20
dB 8.0 8.2 8.5 8.7 8.9 9.0 9.2 9.3 9.4 9.5
================================================================


cu, Andre

Use a wave editor such as CEP/SF/Wavelab equipped with the Waves Direct X plugin - Waves Q 10 Paragraphic software preset "DAT-CD de/pre-emphasis".

@ André

To what software package does this 'Waves Direct X plugin - Waves Q 10 Paragraphic software preset' belong? I only have CEP but this plugin isn't included there...

I now have tested the ***Waves Direct X plugin - Waves Q 10 Paragraphic software preset "DAT-CD de/pre-emphasis". ***.
This is just a 10 band equalizer - for me not precise enough - especially it only flatens the frequency curve approximately, but doesn't consider the question how to correct the in pre-emphasized audio changed time constant.

I'll look for a more accurate tool...

If you have one of those rare old CDs that are pre-emphasized you will want to de-emphasize the wav files before converting them to MP3s. The encoder in iTunes will automatically perform de-emphasis for such CDs. I have found two of my old CDs were preemphasized: Santana's Beyond Appearences and Pink Floyd's The Wall. One way to see if your CD is pre-emphasized is to open it with Exact Audio Copy (EAC) and look at the far right column. For more information see this post:

http://www.hydrogenaudio.org/forums/...pic=38312&st=0