After learning a lot about equalizers and wanting to improve sound quality of iTunes + my Powerbook, I found a good EQ setting on an old Mac OS X Hints article. The last comment on the article offers some knowledgable information. The writer of the comment also posted the favorite EQ settings used on his/her iBook. I tried out the settings on my Powerbook and they work nicely. I did reduce the 64Hz and 125Hz settings quite a bit due to distortion.
Here are the setttings in use for my Powerbook (each tick on the EQ sliders equal 3dB):
Preamp: -3.5dB
32Hz: -12dB (all the way down)
64Hz: 1.5dB
125Hz: 5dB
250Hz: 1dB
500Hz: -5dB
1KHz: -3dB
2KHz: 0dB
4KHz: -1dB
8KHz: 1dB
16KHz: 3dB
Of course, these are subjective.
AppleScripts
You can make equalizer settings using AppleScript. Pase the following code into Script Editor to apply the equalizer settings above:
tell application "iTunes"
set the current EQ preset to EQ preset "Manual"
tell EQ preset "Manual"
set band 1 to -12
set band 2 to 1.5
set band 3 to 5
set band 4 to 1
set band 5 to -5
set band 6 to -3
set band 7 to 0
set band 8 to -1
set band 9 to 1
set band 10 to 3
set preamp to -3.5
end tell
end tell
You can download the Powerbook iTunes EQ script file.
Finding EQ Settings
Technically, the goal of an equalizer is to restore the original recording from the abuse dealt to it by imperfect speakers, etc., not to somehow enhance the sound. Given a recording that contains a variety of tones at the same volume level, ideal speakers would produce each tone at 0dB—a flat frequency response. This never happens; the frequency response usually drops off at the low and high ends, and has various fluctuations. If you have the frequency response graph for a set of speakers or headphones, the general idea is to set the EQ to flatten out curve (for example, cutting the 500Hz band by 2dB if the frequency response curve is 2dB above average at 500Hz). For headphones, HeadRoom is a good source of such information.
Being unable to find such graphs for my headphones, I empirically (though not in any way scientifically or professionally) chose equalizer settings for them in the following manner:
I created a sound file with the Audacity application. The sound file contained one second each of ten pure townes, having frequencies equal to each of the ten bands of the iTunes EQ: 32Hz, 64Hz, 125Hz, etc. I saved the file as an MP3 and copied into my iTunes library. Then I played the sound repeateldy in iTunes using the Flat equalizer setting. According to my ears (not a microphone or some other less-subjective equipment), some tones were obviously louder or softer than others. I then just adjusted the EQ until the tones were roughly equal in loudness. Note that the 64Hz and 32Hz tones are unlikely to respond much at all on cheaper speakers or headphones, and you 16KHz will not appear as loud either (some people may not be able to hear it at all). It was clear that my headphones could not reach 32Hz, so I put the slider all the way down for that band. The final step is to try out a variety of music styles to check for unnatural sounds, distortion, etc. I found a bit of distortion so I lowered the preamp setting, and ended up tweaking some of the upper bands.
The iTunes EQ test tones are available for download. Turn down the volume before playing it!
Sony MDR-G52 Headphones
For what it’s worth, here are the EQ settings I determined for Sony MDR-G52 headphones, using iTunes on my Powerbook:
Preamp: -3.5dB
32Hz: -12dB (all the way down)
64Hz: 1.5dB
125Hz: 5dB
250Hz: 1dB
500Hz: -5dB
1KHz: -3dB
2KHz: 0dB
4KHz: -1dB
8KHz: 1dB
16KHz: 3dB
You can use the Sony Headphones script file to make these settings.