There are many different possible tunings for a guitar. Some of them can be bewildering to a beginner. Tuning a guitar down a quarter-step is one of the more difficult tunings, but it can be done by a beginner with proper instruction. A musical “step” is a whole tone, or two semi-tones, and would be represented by two frets on a guitar. A half step is then one fret, and a quarter would be equivalent to half a fret.
Ensure that the guitar is tuned to the relevant tuning. Generally, you will want to tune down a quarter-step from standard tuning (E, A, D, G, B and e), but the song might require it to be done from drop-D tuning or any other variation.
Play the thick, top string at the fifth fret, and compare it to the string underneath with nothing fretted. The notes should be equal if you’re in standard tuning. If you’re in drop-D tuning (D, A, D, G, B, e) you have to press the seventh fret to get an equal tone. Note the position of the machine head for the top string.
Turn the tuning head to slacken the string. The aim is to lower the pitch of the thick string so that you need to play it at the sixth fret to produce a note equal to the string below. When the note is equal, look at the new position of the machine head. You’ve just tuned the string down by a half-step, and you’re likely to have turned the machine head around by about 45 degrees. If that is different, don’t worry — it depends on your tuner’s gear ratio.
Turn the tuning head to tighten the string, but only turn the machine head half way back to the starting point. This string is now in, or very close to, a quarter-step down tuning. This is not an exact science. You might need to adjust it according to the sound for which you are searching, but it will get you in the right area.
Retune the remainder of the strings on your guitar. Now, the E (or thickest) string is tuned a quarter-step down, you can play the note at the fifth fret and tune the A string (the next one down) to match the pitch produced. Repeat this process once the A string has been synched with the E string, except play the fifth fret on the A string and adjust the D string accordingly. Each tuning head will need a similar degree of adjustment. The only difference in this pattern is when you’re tuning the B string (second string from the bottom) from the note fretted on the G string (third from bottom). Play the fourth fret on the G string and match that pitch with the B string. Tuning from the B to the e string does back to the fifth fret.
If you have an electric tuner, simply drop the pitch of each note down by around 40Hz to achieve quarter-step down tuning.