The signal/noise ratio (or SNR) is an important concept to assess the quality of a product. Particular attention is often neglected in the flood of technical characteristics announced. Yet it is one of the simplest values to understand.
What is SNR
In any amplifier there is noise. This noise is caused by the random movement of electrons within resistors and semiconductor components (due to temperature) and even any expensive Hi-Fi device such as the best integrated amps under $ 3000 is liable to this. The voltage representing this noise is superimposed on the voltage representing the useful signal.
Noise is therefore a signal which contains harmonics at all frequencies and with the same amplitude. One possibility to quantify the noise is the signal to noise ratio SNR (Signal to Noise Ratio). The definition of SNR in dB is as follows:
- SNR = P signal / P noise
- SNR is the signal to noise ratio in decibels [dB]
- P signal is the useful signal strength in watt [W]
- P noise is the noise power in watts [W]
The causes of noise
In our audio frame, we come across this noise all the time, impossible to separate from it. Electronic and acoustic components are full of small flaws. When they are assembled to form a complete product, the defects accumulate.
Add to that a few unnoticed design flaws and the final cocktail get pretty damn loud. And we haven’t even addressed the problem of analog-to-digital or digital-to-analog conversions.
A good signal to noise ratio for an amplifier
The value indicating the dynamic range in decibels (dB) between the internal noise of a device (hiss when no signal passes through it) due to the components themselves, and the maximum level before saturation (clipping or significant distortion). A good signal to noise ratio is 60 dB for a phono turntable, 90 dB for an amplifier or CD, 100 dB for a preamp. Note that the signal/noise ratio of a domestic room (background noise from the street and the wind/level bearable by the ears) is of the order of 80 dB.