Hello,
As many before, I've been looking for the "best" digital de-emphasis method so as to listen to my music properly on my computer.
I've compared the resulting files of three de-emphasis methods applied to the song "Ecplise" of The Dark Side Of The Moon - Japan Harvest Black Face (Matrix: CP353017 10A1).
Audacity with a custom EQ curve based on the ISO 908 standard, originally posted by foobar2000[/li]
I've applied the following curve to the FLAC rip of Ecplise with its pre-emphasis untouched, with a 32bits resolution on Audacity before exporting to 16bits FLAC:
<curve name="De-Emphasis">
<point f="510.000000000000" d="-0.100000000000"/>
<point f="726.000000000000" d="-0.200000000000"/>
<point f="896.000000000000" d="-0.300000000000"/>
<point f="1042.000000000000" d="-0.400000000000"/>
<point f="1173.000000000000" d="-0.500000000000"/>
<point f="1294.000000000000" d="-0.600000000000"/>
<point f="1408.000000000000" d="-0.700000000000"/>
<point f="1516.000000000000" d="-0.800000000000"/>
<point f="1620.000000000000" d="-0.900000000000"/>
<point f="1720.000000000000" d="-1.000000000000"/>
<point f="2188.000000000000" d="-1.500000000000"/>
<point f="2629.000000000000" d="-2.000000000000"/>
<point f="3064.000000000000" d="-2.500000000000"/>
<point f="3506.000000000000" d="-3.000000000000"/>
<point f="3965.000000000000" d="-3.500000000000"/>
<point f="4449.000000000000" d="-4.000000000000"/>
<point f="4968.000000000000" d="-4.500000000000"/>
<point f="5534.000000000000" d="-5.000000000000"/>
<point f="6159.000000000000" d="-5.500000000000"/>
<point f="6861.000000000000" d="-6.000000000000"/>
<point f="7664.000000000000" d="-6.500000000000"/>
<point f="8605.000000000000" d="-7.000000000000"/>
<point f="9739.000000000000" d="-7.500000000000"/>
<point f="11157.000000000000" d="-8.000000000000"/>
<point f="13029.000000000000" d="-8.500000000000"/>
<point f="15708.000000000000" d="-9.000000000000"/>
<point f="20128.000000000000" d="-9.500000000000"/>
<point f="21427.000000000000" d="-9.600000000000"/>
</curve>
SoX 14.3.2 using the deemph command line[/li]
FOR %%A IN (*.flac) DO sox "%%A" "%%A.flac" deemph
full EQ curve based on the ISO 908 standard[/li][/list]
The first EQ curve I took from foobar2000 (see first point) isn't actually complete, and though the two following frequencies are not anymore within the audible frequency range, they should be added (at least the first one) on a theoretical point view, to help filtering the frequencies between 21427Hz and 22050Hz (Shanon's frequency).
<point f="30195.000000000000" d="-10.00000000000"/>
<point f="96000.000000000000" d="-10.40000000000"/>
I actually added them because I found out that the first Audacity EQ curve gave me more treble in the very upper range (though that's not the one you can really hear, dogs are happier about that ) than SoX.
[blockquote]The results are as follows:
[a href="http://imageshack.us/photo/my-images/269/deemphasistdsotm.png/" target="_blank"] :SoX de-emphasized minus Audacity de-emphasized with the complete EQ curve.[/li][/list]
Short and unpretentious analysis plus a few comments:
The graph is self-explanatory to me. SoX algorithm and calculation are fairly good when compared to the custom EQ curve based on the ISO 908 standard I used in Audacity. I guess it does use 32bits to EQ the curve before exporting to 16bits relying on the accuracy of the plots, in a nutshell, exaclty what Audacity did. Nevertheless, you can notice that SoX does not go as far as the ISO based complete EQ curve de-emphasis method, according to the very upper treble it left (well above 20kHz, TDSOTM pre-emph minus SoX TDSOTM de-emph ~ 0dB).
It should also be noted that the Audacity's files have a 15kbps higher average bitrate than the SoX's files, both using 8 level FLAC .
Both have average bitrates which are more or less 50-65 kbps lower than the pre-emphasized files, there's no wonder about that however.
Regarding sonics? Huh, they actually sound pretty much the same (all the de-emph's I mean ), if not exactly, and even though my mind tells me that the Audacity full curve de-emphasized method sounds slightly better, I'm deeply convinced it all boils down to the graphs for us lesser mortals.
What will I use? Audacity with the full EQ curve. Firstly because this method shows a more consistent theoretical performance, and also because it's more convenient to use: you can do batch de-emphasis and 16bits FLAC exporting of several files quite simply (using included scripts "editor", ask if needed).
Feel free to comment or point out anything wrong .