Tuning a bass guitar can be a very difficult at first. It takes practice and is mostly by the ears. Do not expect to get it right on a first take. The first thing you need to remember is that a typical bass guitar has four notes- E, A, D, G,. For a five string you have a lower B; while on a six string you have a high C. But the most important thing to remember is that standard tunings adhere to the tuning of E,A,D,G. Next, you need to loosen up your chords. You do not want any of your chords snapping because of over tightening. It is better to loosen them down and work your way from there.
A bass guitar that is out of tune has basically clashing notes. You need to listen to a standard tone of a well tuned bass guitar to determine the basic sound of open notes between the E, A, D and G strings. From there, you will have a great idea which string is out of tune.
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A standard tuning starts with the lowest string-the E string; from there, you need to work your way up to the G or in some bass guitars, the C. It is good to have a piano to get the standard E note; if you don't have one, then you just have to play it from whatever note it is and tune the bass in relation to that note.
As illustrated below, place your fretting finger on the fifth of the E string then pluck it. E string is the thickest string of your bass guitar.
G-----------
D-----------
A-----------
E----5------
While fretting the E string, simultaneously pluck the open A string. An open string means you are not fretting it.
G-----------
D-----------
A---0-------
E----5------
That is why you need to loosen up your strings to find out whether you need to go up or down the scale to "chase" the tune of the fretted E string. Adjust the tuning of your A string until both have the same pitch. What you need to listen while doing this is the wobbling or "wah" tone; it should never be there. Adjust the open A chord until the "wah" tone disappear.
You have to repeat the same procedure for the D and G strings. There are many ways to tune your bass guitar other than the 5th fret method. By far, this is the most common and the cheapest of all.
How To Tune a Bass Guitar