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Most 'true' way to de-emphasize CD image, Remove pre-emphasis - possible and best ways?
EvilMax
post Aug 2 2008, 13:46
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Hello!

Have a question related to de-emphasizing of images of audio CDs mastered with pre-emphasis. What I've already found on this topic:

1. Using Waves Q10 plugin. But it seems to me that equalizer plugin is not the best way to achieve originally mastered sound.
2. Using foobar2000 convolver with Waves_De-Emphasis pulses. Don't know anythig good/bad for this way.

So does anybody knows what way is 'true' to de-emphasize wave file?

PS: I know that using EAC or K3b to burn CD and delegate de-emphasizing to CD player will solve issue. But for some reasons I need to have images on my PC and ability to play them or several tracks on players that don't support 'pre' flag.
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pdq
post Aug 2 2008, 14:46
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Are they still making CDs with pre-emphasis, or are these some pretty old discs?
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Egor
post Aug 2 2008, 15:17
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You can de-emphasize using sox (a command line program).
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EvilMax
post Aug 2 2008, 15:38
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QUOTE (pdq @ Aug 2 2008, 16:46) *
Are they still making CDs with pre-emphasis, or are these some pretty old discs?

This is rather old discs. For example, first masters of early Pink Floyd or Deep Purple albums.

Egor, I've looked to side of sox. By some opinions it almost kills stereo from tracks sad.gif
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M
post Aug 2 2008, 15:51
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QUOTE (EvilMax @ Aug 2 2008, 10:38) *
Egor, I've looked to side of sox. By some opinions it almost kills stereo from tracks sad.gif


Eh? News to me. Could you post an example where SoX "kills" stereo, or refer us to some notes/opinions that explain how and why? SoX has a bit of a learning curve, so I suspect this is simply a case of someone's parameters not being quite right.

- M.
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EvilMax
post Aug 2 2008, 16:22
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QUOTE (M @ Aug 2 2008, 17:51) *
QUOTE (EvilMax @ Aug 2 2008, 10:38) *

Egor, I've looked to side of sox. By some opinions it almost kills stereo from tracks sad.gif


Eh? News to me. Could you post an example where SoX "kills" stereo, or refer us to some notes/opinions that explain how and why? SoX has a bit of a learning curve, so I suspect this is simply a case of someone's parameters not being quite right.

- M.

I don't remember exactly a link to tests of stereo damaging (I'll try to find it), but here http://www.hydrogenaudio.org/forums/lofive...php/t62156.html I've found reference someone's opinion that sox can damage the sound durind de-emphasizing process.
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sbooth
post Aug 2 2008, 16:37
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CD de-emphasis was originally designed to be done in the analog domain. If you want to do it digitally the best way is to process the file at 24 bits (or higher) then either leave it at the higher bit depth or dither it back to 16. If you process it at 16 bits you will definitely lose fidelity. Unfortunately I'm not familiar enough with the SoX internals to know how its effects are applied.
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Surfi
post Aug 2 2008, 16:57
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Using Waves Q10 too. Tried Sox before but did hear a difference in stereo extensiveness (much better with Waves).

Surfi.
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benski
post Aug 2 2008, 18:38
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Yes, de-emphasis is meant to be done in the analog domain.
Two reasons:
1) That high 15us zero doesn't have enough resolution to do well in the digital domain.
2) The de-emphasis can produce peaks that would clip in the digital domain.
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greynol
post Aug 2 2008, 18:47
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QUOTE (Surfi @ Aug 2 2008, 08:57) *
Using Waves Q10 too. Tried Sox before but did hear a difference in stereo extensiveness (much better with Waves).

How is a de-emphasis filter going to interfere with stereo information?


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Glenn Gundlach
post Aug 2 2008, 19:00
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QUOTE (benski @ Aug 2 2008, 09:38) *
Yes, de-emphasis is meant to be done in the analog domain.
Two reasons:
1) That high 15us zero doesn't have enough resolution to do well in the digital domain.
2) The de-emphasis can produce peaks that would clip in the digital domain.


All true but once the file is ripped it has to be fixed. In Audition I use this FFT filter and I'm pretty happy with it. Log scale and spline curves on.

21.53 Hz 0dB
1241.7 Hz 0dB
1552.49 Hz 0dB
2386.17Hz -0.6dB
3330.31 Hz -2.4dB
6228.9Hz -6.3dB
8097.04 Hz -8.4dB
10851 Hz -9.6dB
22050 Hz -9.9dB

This filter will do nothing at all to stereo separation as it is done identicallly to the 2 channels with no 'blending'.
I asked this several months back. Is there any software that absolutely identifies pre-emphasis yes/no ?

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Egor
post Aug 2 2008, 19:08
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QUOTE (EvilMax @ Aug 2 2008, 21:38) *
Egor, I've looked to side of sox. By some opinions it almost kills stereo from tracks sad.gif

No need to worry! You've run in some misinformation.

Right now I've prepared a test audio cd with two tracks. Here is the cuesheet for burning:
QUOTE
FILE "test.wav" WAVE
TRACK 01 AUDIO
FLAGS PRE
INDEX 01 00:00:00
FILE "test-deemph.wav" WAVE
TRACK 02 AUDIO
INDEX 01 00:00:00

I don't have any real CDs with preemphasis, so I de-emphasized a normal CD track with sox:
QUOTE
C:\audio>sox test.wav test-deemph.wav deemph


When played back in a standalone CD player, one would hear "hardware" de-emphasis for the first track, and software de-emphasis for the second track.

So, I have just played back the freshly-burnt CD-RW in my Panasonic SL-CT820 portable CD player and guess what - I have not heard any difference between the 1st and 2nd tracks. Unfortunately I ain't got no SPDIF-in capture device to grab CD player's optical out, so here's my feedback in text form only.

This post has been edited by Egor: Aug 2 2008, 19:37
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EvilMax
post Aug 2 2008, 19:32
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It is all very interesting, thank you for information. So as far as I understood converting WAV to 24 bit, then de-emphasizing using SoX or Adobe Audition and then dithering to 16 bit could help levae fidelity almost intact. Interesting, is there information about de-emphasizing filter curve used in SoX anywhere ?

Found also information about tool written by acoustic engineer mr. Ahlersmeyer: that could be found at http://www.picosound.de/ Did someone tested this? I have Vista so this tool don't wanna run even in Win98 compatibility mode.

PS: what software could be recommebded for 16-24 and 24-16 bits transformations?
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Egor
post Aug 2 2008, 19:41
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QUOTE (EvilMax @ Aug 3 2008, 01:32) *
Interesting, is there information about de-emphasizing filter curve used in SoX anywhere ?

SoX is open source by the way wink.gif Looking at the source may help somehow, even if don't speak C.
For bit-depth coversion use foobar2000.

@Glenn. Goldenhawk's CDRWIN can instantly display flags (incl. PRE) for a CD. Use the "Table of contents" command.

This post has been edited by Egor: Aug 2 2008, 20:01
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M
post Aug 2 2008, 20:03
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According to the changelog, the deemphasis filter was also changed from 1st order to 2nd order with the release of 14.0.0 (2007/09/11).

- M.
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EvilMax
post Aug 2 2008, 20:04
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QUOTE (Egor @ Aug 2 2008, 21:41) *
QUOTE (EvilMax @ Aug 3 2008, 01:32) *
Interesting, is there information about de-emphasizing filter curve used in SoX anywhere ?

SoX is open source by the way wink.gif

Already reading. I did not found any arrays with coefficients. It seems that it uses some implementation of digital filter and it is possible to reconstruct curve, but I need to extract formulae at first.
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Sebastian Mares
post Aug 3 2008, 11:08
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Did anyone check how well iTunes deemphasizes CDs?


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http://listening-tests.hydrogenaudio.org/sebastian/
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markanini
post Aug 3 2008, 12:02
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I have tried Sox and WaveEmph and comparing the spectrum of a single impulse I saw the cutoff point for Sox de-emphasis process is higher and rolls of faster. Not sure which one is truer to spec but the developer of WaveEmph states his program is 0.2 db within spec while I found no documentation on Sox de-emphasis feature. I personally use the ImpulsEmph.wav files included in WaveEmph together with foobar2000 convolver plug-in for convenience. Hope this helps.
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tot
post Aug 3 2008, 15:40
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sox with --plot option and deemph will plot the filter function.


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Surfi
post Aug 3 2008, 16:17
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QUOTE (greynol @ Aug 2 2008, 19:47) *
How is a de-emphasis filter going to interfere with stereo information?

I've no idea. It shouldn't if well implemented (trusted my ears those days). I've been comparing actual SoX and Waves and WaveEmph today and couldn't ABX the results. Either SoX has been improved or my ears have changed for the worse. If anyone's interested (and it doesn't violate the forum rules) I can upload the files and post the links.

Surfi

This post has been edited by Surfi: Aug 3 2008, 16:44
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bandpass
post Aug 8 2008, 18:55
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QUOTE (Surfi @ Aug 3 2008, 15:17) *
Either SoX has been improved or my ears have changed for the worse.


The sox changelog says that the deemph stereo bug was fixed in sox-12.18.2 (2006-09-03).

Also the latest doc on the sox website has some words on the accuracy:

The de-emphasis filter is implemented as a biquad; its maximum deviation from the ideal response is only 0.06dB (up to 20kHz).

-bandpass
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markanini
post Aug 10 2008, 02:58
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QUOTE (bandpass @ Aug 8 2008, 18:55) *
QUOTE (Surfi @ Aug 3 2008, 15:17) *

Either SoX has been improved or my ears have changed for the worse.


The sox changelog says that the deemph stereo bug was fixed in sox-12.18.2 (2006-09-03).

Also the latest doc on the sox website has some words on the accuracy:

The de-emphasis filter is implemented as a biquad; its maximum deviation from the ideal response is only 0.06dB (up to 20kHz).

-bandpass

this is interesting, could you provide a link? Certainly more than WaveEmphs < 0.2 dB claim...
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Surfi
post Aug 10 2008, 11:00
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QUOTE (markanini @ Aug 10 2008, 03:58) *
this is interesting, could you provide a link? Certainly more than WaveEmphs < 0.2 dB claim...

Homepage (I think you know that ...):
http://sox.sourceforge.net/

Effects manual:
http://sox.sourceforge.net/soxeffect.html
(do a search for biquad or deemph on that page)

Downloads:
http://sourceforge.net/project/showfiles.php?group_id=10706


Here's a link to an older (2006) german page that is providing files for testing a deemphasis filter.
http://www.radonmaster.de/robernd/tAFILTER.html


Surfi

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Aquares
post Nov 13 2009, 20:15
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Tested with Denon Audio Technical CD (1984), Tracks 36-39, WaveEmph is better.

SoX has a deviation of about +0.02/-0.18dB, whereas WaveEmph has +/- 0.03.

This is the sweep with emphasis (scale 2dB, original level):


The result from WaveEmph (scale 0.1dB, shifted to 0dB at 1kHz):


And from SoX (scale 0.1dB, shifted to 0dB at 1kHz):


There is some measurement inaccuracy at lower frequencies.

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Wombat
post Nov 14 2009, 02:19
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Never saw someone offering such measurements, thanks for that.
One thing i wonder how accurate the Denon original sweep really is and how it was created. Reading a while back about pre-emphasis even the studio machines didn´t apply the curve always correct and had tolerances.
Out of curiosity it may be intersting if you can get an output of the foobar convolver plugin some recommended or the Waves Q Equalizer itself.

Edit: Here for example someone measured his Sony PCM-601 and it wasn´t 100% accurate by applying de-emphasis http://www.radonmaster.de/robernd/tAFILTER.html

This post has been edited by Wombat: Nov 14 2009, 02:41
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