Signal-to-Noise Ratio and Why It Matters

A decibel meter.

 

Bernd Schunack / Getty Images 

You might have come across a listed product specification, or maybe even heard or read a discussion about signal-to-noise ratio. Often abbreviated as SNR or S/N, this specification can seem cryptic to the average consumer. While the math behind signal-to-noise ratio is technical, the concept is not, and this value can impact a system's overall sound quality.

Signal-to-Noise Ratio Explained

A signal-to-noise ratio compares a level of signal power to a level of noise power. It is most often expressed as a measurement of decibels (dB). Higher numbers generally mean a better specification, since there is more useful information (the signal) than there is unwanted data (the noise).

For example, when an audio component lists a signal-to-noise ratio of 100 dB, it means that the level of the audio signal is 100 dB higher than the level of the noise. A signal-to-noise ratio specification of 100 dB is considerably better than one that is 70 dB (or less).

For illustration, let's say that you're having a conversation with someone in a kitchen that also happens to have a particularly loud refrigerator. Let's also say the refrigerator generates 50 dB of hum (consider this as the noise) as it keeps its contents cool—a loud fridge. If the person you are speaking with chooses to converse in whispers (consider this as the signal) at 30 dB, you won't be able to hear a single word because it is overpowered by the refrigerator hum! So, you ask the person to speak louder, but even at 60 dB, you may still be asking them to repeat things. Speaking at 90 dB may seem more like a shouting match, but at least words will be clearly heard and understood. That's the idea behind signal-to-noise ratio.

Why Signal-to-Noise Ratio Is Important

Specifications for signal-to-noise ratio can be found in many products and components that deal with audio such as speakers, telephones (wireless or otherwise), headphones, microphones, amplifiers, receivers, turntables, radios, CD/DVD/media players, PC sound cards, smartphones, tablets, and more. However, not all manufacturers make this value readily known.

The actual noise is often characterized as a white or electronic hiss or static, or a low or vibrating hum. Crank the volume of your speakers all the way up while nothing is playing—if you hear a hiss, that's the noise, which is often referred to as a "noise floor." Just like the refrigerator in the previously described scenario, this noise floor is always there.

So long as the incoming signal is strong and well above the noise floor, then the audio will be able to maintain a higher quality. That's the kind of good signal-to-noise ratio people prefer for clear and accurate sound.

But if a signal happens to be weak, some might think to simply increase the volume in order to boost the output. Unfortunately, adjusting the volume up and down affects both the noise floor and the signal. The music may get louder, but so will the underlying noise. You would have to boost only the signal strength of the source in order to achieve the desired effect. Some devices feature hardware and/or software elements that are designed to improve the signal-to-noise ratio.

Unfortunately, all components, even cables, add some level of noise to an audio signal. It's the better ones that are designed to keep the noise floor as low as possible in order to maximize the ratio. Analog Devices, such as amplifiers and turntables, generally have a lower signal-to-noise ratio than digital devices. 

It is definitely worth avoiding products with very poor signal-to-noise ratios. However, signal-to-noise ratio should not be used as the only specification to measure the sound quality of components. Frequency response and harmonic distortion should also be taken into consideration.