One of the ways to to tune a classical guitar is by using reference notes. You listen to a note for each string and tune them, one by one, until they sound the same as the reference note. You then carry on with the rest of the strings until they sound suitable for classical guitar playing. It’s not easy, but, it means you will be self sufficient and have a good ear for notes.
One short cut to get a reference note is to use a tuning fork. Tuning forks always emit the same note when struck. The vibration has a resonance of 440HZ; the fourth octave. Once you know that an octave is the sound that separates a note into two, you can use that to tune your guitar.
An octave is the part of the note that you can hear with least distortion so it is a great thing to use when tuning your guitar; an octave is in the middle of the spectrum so you will be able to process the sound much more easily.
The classical guitar also has its own special tool: a whistle. A tuning whistle has six separate whistles that are tuned for each of the six strings of the Spanish classical guitar. The tuning whistle works in a similar way to the tuning fork as each whistle will only ever emit the exact note needed for tuning. The tuning whistle has an advantage over the tuning fork as you have 6 different notes.
Of course, there are electronic tuners that use software to detect how distorted the note you are playing is. You are also aided by a visual diagram to help you identify the note of each string. There are 3 modes on most electronic tuners; acoustic guitar, electric guitar and a custom setting, that you can adjust to get your own unique sounds.
Electronic tuners are great but, you should always learn how to tune your guitar by ear first. Electronic tuners are not always 100% correct or they are too correct and mean that for some songs the exact tuning may not suit the mood of the song.
We recommend that you use the software first to see how the notes sound. Then check with a tuning fork and/or tuning whistles. And, then, you should check the feeling of the sound. If you use a combination of tuning techniques, you will be able to use short cuts when they are needed but be able to rely on your own ears if you would like to come up with your own tunings to stand out from the crowd.