This question pops up every once in a while among guitarists: why would I tune down a semitone? Well, there are certain benefits in tuning down a half-step to E♭ (E flat, or E bémol), along with your entire band, of course. These are:
1 Songs sound heavier
Or somehow “fuller”. I’m avoiding “darker”, I think that characteristic has more to do with the actual composition than with the tuning. The pitches we use were selected by measuring the distance from a base selected more or less arbitrarily. The are relative to the reference pitch. Moving that reference down or up may bring all the pitches of a song into an area that has a different overall emotional impact and “feel”.
2 Male vocal parts are easier to sing
This is a big deal. Tuning down even as (apparently) little as one semitone can have a huge impact on a singer’s performance, when you think about the (arguably) most important and challenging technique a singer has to master: bridging between the chest (modal) and head register pitches, through the so-called zona di passagio.
These are the most difficult notes for any singer, it’s where the voice feels “wobbly”, like it’s going to “fall” into head voice or falsetto, resulting in that horrible “yodel” sound that every singer (and his band, and his public) dreads. There’s just one semitone at each end of this zone. The infamous “yodel” takes but a mere half-step to occur (give or take, remember that these pitches are ultimately arbitrary), so taking the song down by a half-step may be just what makes the singer comfortable with it.
Even a great singer like Bon Jovi, whose “money notes” hover around B4/C5 (the operatic tenor upper limit) may be helped greatly by tuning down, changing these notes to A4♯-B4. In fact, Bon Jovi now down-tunes to E♭ live due to Jon’s age-related loss of range.
3 Guitar feels easier to play
Since string tension is directly proportional with pitch, lowering the pitch decreases the string tension. If you continue to use the same string gauge, the strings will fill less tensed, easier to depress and bend, making the guitar feel easier to play. Don’t forget to readjust your action and neck relief, they may be thrown off by the new string tension.
4 Heavier gauge strings are easier to play
If you need heavier strings (for many possible reasons, of which I only endorse tension and playing “feel”), but don’t like the increased tension that comes with the territory, tuning down alleviates the problem. Tuning down to E♭ allows you to go up in gauge by one step (e.g., 0.009s to 0.010s), while maintaining the overall feel of the strings. A famous example is Slash.
Tuning down to E♭ should be seen simply as standard tuning but using as reference A4=415 Hz, instead of the international modern standard of A4=440 Hz. After all, unlike other alternative tunings, it does not alter the relationships between strings, so the guitar is played exactly the same way.
Interestingly, although the relativity of pitch stays the same, tuning down seems to change the way you hear the music, and especially the kind of ideas you get while writing on a tuned-down guitar, so I would encourage anyone to try it, it takes but a few minutes, and can be temporarily undone with a capo on the first fret, so you can easily go back and forth between tunings.
Most baroque music was played using A-415 as reference. Back to the mid-nineteenth century, there was hardly a standard pitch between the many orchestras and places where music was played. The overall tendency was for a higher reference, probably because higher sounds are perceived better, and it went as far as violin strings snapping and voices unable to keep up with it. So was the A-440 standard born, and you have to remember it’s just an semi-arbitrarily chosen convention.
Some people consider E♭ tuning as singers cheating, but I think that is plain stupid. In music we go by “whatever works”. You’ll find a lot of big names on this list, some of which made history (Jimi Hendrix – pictured, Van Halen, Yngwie Malmsteen, etc.).