Signal-to-Noise Ratio Explained
A signal-to-noise ratio compares a level of signal power to a level of noise power. It’s most often expressed as a measurement of decibels (dB). Higher numbers generally mean a better specification since there’s more useful information (the signal) than unwanted data (the noise). For example, when an audio component lists a signal-to-noise ratio of 100 dB, it means that the audio signal level is 100 dB higher than the noise level. Therefore, 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 a friend in a kitchen who also happens to have a particularly loud refrigerator. Let’s also say that the refrigerator generates 50 dB of hum—consider this the noise—as it keeps its contents cool. If the friend you’re speaking with is whispering at 30 dB—consider this the signal—you won’t be able to hear a single word because the refrigerator’s hum overpowers your friend’s speech. You may ask your friend to speak louder, but even at 60 dB, you may still need to ask them to repeat things. Speaking at 90 dB may seem more like a shouting match, but at least words will be heard and understood. That’s the idea behind the signal-to-noise ratio.
Why Signal-to-Noise Ratio Is Important
You can find specifications for signal-to-noise ratio can in many products that deal with audio, including 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. As long as the incoming signal is strong and well above the noise floor, the audio will maintain a higher quality, which is the kind of signal-to-noise ratio preferred for a clear and accurate sound.
What About Volume?
If a signal happens to be weak, you might think you need to increase the volume 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 to achieve the desired effect. Some devices feature hardware 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. The best components are designed to keep the noise floor as low as possible to maximize the ratio. Analog devices, such as amplifiers and turntables generally have a lower signal-to-noise ratio than digital devices.
Other Considerations
It is definitely worth avoiding products with very poor signal-to-noise ratios. However, the signal-to-noise ratio should not be used as the only specification to measure the sound quality of components. Frequency response and harmonic distortion, for example, should also be taken into consideration.
