Signal-to-Noise Ratio (SNR) Explained
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Product specifications often list the signal-to-noise ratio, sometimes written as "SNR" or "S/N," but what does it mean? While the math behind SNR is technical, the concept is not, and this value can impact a system's overall sound quality. SNR compares the level of a signal to the level of noise. In other words, it compares the ratio between the relevant (wanted) and the irrelevant (unwanted) information. It is most often expressed as a measurement of decibels (dB). Higher numbers generally mean a better sound quality, since there is more useful information (the signal) than there is unwanted data (the noise). A decibel is a logarithmic ratio in which every 20 dB represents a factor of 10. For example, going from 80dB to 100dB means increasing by 10 times. This means that an audio component having an SNR of 100 dB will have 10 times less noise than one that has 80 dB. The chart below shows how different dB ratios actually compute.
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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) — 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. Our PecanPi® products have a SNR of 130 dB or 3,162,277 : 1.
(Edited)
thumb_upkeyboardfanatic, han, and 4 others
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MartijnvanderStar
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Jan 3, 2020
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But what is meant with the unwanted signals? Signals from the electrical audio device? The CD? And what are these signals? How do they exist, how are the generated, where do they come from, why are they there too? Questions, questions and more questions.
Jan 3, 2020
kevemaher
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Jan 13, 2020
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All of the components in the signal chain generate noise. A large part of the noise is random noise, meaning that all frequencies are equally represented. A typical source is an opamp or transistor. Source for this noise is most often thermal. Resistors can generate noise. All active and passive components contribute. This type of noise is difficult to filter out. Balanced cables can improve the SNR by about 1.4x, by summing two signal paths for the same source signal. The signal we want increases by a factor of 2, but the noise, since it is random, increases by a factor of square root of two. Other types of noise have some frequency components such as "hum" which is at 60, 120, 180 Hz, etc. This can be filtered down, but never fully removed in the power supply. Noise is a very important topic, since it exists in everything we do, see, and hear. There are numerous guides on the web.
Jan 13, 2020
kevemaher
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Jan 16, 2020
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To continue the conversation about noise, there is another important noise source - the signal itself. Due to the statistical nature of the signal, the rate of signal input varies a bit with time. This variation is equal to the square root of the signal. This source of noise must always be considered. A design goal is to make the signal the largest source of noise, since this noise cannot be engineered away, like other sources such as thermal.
Jan 16, 2020