Find Easy Solutions

The easiest way is to adjust the frequency produced by any instrument to the right pitch.

For example, in Guitar, the E string vibrates at the frequency of 329.63Hz. If you pluck the first string, the software shows 329.6Hz and show the E4 note.
Looking at the physics of a vibrating string, the lowest frequency produced by any instrument is called the fundamental frequency.  The fundamental frequency is also known as the first harmonic of the instrument.  329.63 Hz is the fundamental frequency of the E string.

PitchPerfect Guitar Tuner is a free software by NCH  Software designed to tune different verity of string instrument like Guitar, violin, Cello ,etc.. it allows you to identify the frequency of the sound  played and automatically detects the note.


Here is the link for the software

You can find the fundamental frequency of open strings in the following tables.

Guitar 

Standard

String tuning	1	2	3	4	5	6
Note	E4	B3	G3	D3	A2	E2
Frequency (Hz)	329.63	246.95	196.00	146.83	110.00	82.41

Open G tunning

String	1	2	3	4	5	6
Note	D4	B3	G3	D3	G2	D2
Frequency (Hz)	293.66	246.95	196.00	146.83	98.00	73.42