The higher the signal-to-noise ratio, the better. It's also written as S/N ratio.
In electronic processing of sound, the desired sound is called "signal", unwanted sound is "noise". Unwanted sound or noise here means sound that was not present in the original source, but was introduced as a result of imperfections in the electronics. The most common types of noise are hum, hiss or crackling.
As the name indicates, S/N ratio is the ratio of wanted sound to unwanted sound, and is measured in decibels or db.
Mathematically S/N ratio = 10log{(wanted sound power)/(unwanted sound power)}
If the signal and noise are measured in volts, millivolts or microvolts,
S/N ratio = 20log{(signal voltage)/noise voltage)}
A signal-to-noise ratio of 70db is acceptable. 80-90db is good. 100 db and above is very good.
S/N ratio is also important for many applications of electronics other than sound.
