While there are a number of media players and audio programs that can be used to play music through your Mac, iTunes being a library and content manager as well as a player that comes preinstalled on Mac systems makes it the most popular option out there. The program offers simple controls for sorting through music, generating playlists, and playing your music, but in addition there are some settings that can be used to greatly improve sound quality during playback.
The first of these is the Sound Enhancer setting in the iTunes preferences, which is activated by going to the Playback section of the iTunes preferences and checking the "Sound Enhancer" check box.
This mysterious feature enhances music quality by not only adjusting the treble and bass of the output, but also blending various phase components of the audio across channels and mixing them in stereo to give it more depth. The level of this effect can be adjusted with the slider next to the check box that enables it. I recommend adjusting this setting by playing a song or two without it, then enabling this feature and setting the slider at the extremes of its range to hear the difference, and finally by finding the midrange level that works best for you. The effect will be different for different songs and encodings, so selecting an extremely high setting may, for some songs, result in odd and sometimes unpleasant sounding music.
The next component is the iTunes equalizer, which allows you to adjust the relative power of the frequency ranges in the signal to enhance different aspects of what's being played. Proper equalization of a signal is an art form in its own right, but for starters the following is a decent guideline to use:
- 32Hz: Mainly the power of bangs, thumps, and kicks (i.e., bass drum beats).
- 64Hz: Deep throbbing or rumbling bass signals (i.e., kettle drums or gongs), primarily audible on high-end speakers or those with subwoofers.
- 125Hz: The low-end of most bass instruments
- 250Hz: The beginning of most musical instruments' low-end ranges, including guitar, cello, and piano.
- 500Hz: Deep vocals (i.e., Barry White) and bass instruments.
- 1KHz: Most musical instruments and vocals will be greatly affected starting in this range and going higher.
- 2KHz: Most standard vocals are affected by this range
- 4KHz: The sweet spot for melodic components of music (wailing guitar solos and fancy piano runs, etc.)
- 8KHz: High or sharp crashes and bangs such as cymbals and things that screech will be affected most in this range.
- 16KHz: The "fidelity" range, where adjustments can affect the overall "clarity" of sounds but too much may bring out white noise (high hiss sounds) in the signal.
Equalizer settings depend on both the song being played and the speaker system being used, but a commonly recommended equalizer setting is to enhance around a peak of 125Hz to 250Hz and then also at around a peak of 8KHz, slightly dropping the values surrounding these peaks. Apple includes a number of equalizer presets in the equalizer's menu that you can use as starting points for various genres of music.
Part of the equalizer is the preamp slider, which adjusts the overall gain through the equalizer. By increasing the power in each frequency channel you risk saturating the signal, which pushes it to the edge of its dynamic range, thus clipping it and resulting in static and other harsh sounds. The preamp allows you to equally dial back the power through all frequencies, maintaining the current equalization balance but rolling off any saturation that results from it.
If attended to with care, these two settings in iTunes can be more than enough to greatly enhance the quality of your entire music library, but there may be instances where specific songs or albums might need very unique equalization settings. In these cases you can create a custom equalization setup, then save it using the equalizer's preset menu. Then select the songs you wish to apply the preset to and get information on them by pressing Command-I. In the information window, click the Options tab and choose your new preset from the "Equalizer Preset" menu. You can also adjust the song's volume as well, since some albums or tracks may have been recorded at quite significantly lower volumes than others.
Unfortunately the sound enhancer does not have a per-song assignment option, so if you find songs that this does not work for, then you will have to turn it off in the iTunes preferences.
In addition to these equalization options, iTunes supports several other options to enhance your music playback. The first is a cross-fade feature that will blend the last few seconds of a song into the first few of the next song, similar to what is commonly done in radio broadcasts. This will give your library a more continuous feel, but will also cut out some dramatic (and subjectively significant) beginnings and endings to songs so it may not be the most desired option.
A second feature is Apple's Sound Check, which will scan your entire library and adjust individual song volumes so they match. While convenient in some cases, this can adversely affect many albums that include tracks that are meant to be relatively silent. It will also interfere with albums that are built for the tracks to be played seamlessly, where as one track leads into another you may hear a sudden volume jump as iTunes adjusts it.
The options discussed so far deal with the music as-is in your library. However, those who started accumulating digital music years ago may have a number of poorly encoded tracks in their libraries. When people first began collecting music on computers, the standard format was MP3 encoded at 128Kbps, which saved space at between 3MB to 5MB per music file, but it did cut down on quality (especially the highs and lows). These days the use of 256Kbps AAC and other formats offers a higher quality option, but while you can get around this by purchasing new copies of these songs, this may not be feasible or worth it. To fill this gap, Apple offers its iTunes Match service which will look up a song in its iTunes Store and if available will play the higher quality version instead of the one on your computer. This service does cost $25 per year and does require an Internet connection, but allows you to have higher quality music on all of your iCloud-enabled devices.
A last detail to mention with regard to audio quality is that the media player and audio files are only half of the equation. The second aspect is the audio system itself. If you have a cheap set of speakers or headphones, then you will only get so far by adjusting audio settings in iTunes. If you are interested in getting the most out of your music then you might consider an upgrade to your audio hardware. However, this quality argument also goes both way: if you have a fancy audio system but do not properly equalize it and use poor quality audio files, then you are not taking advantage of its capabilities.