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Signal-to-Noise Ratio
Remember the last time you were trying to have a conversation in a crowded room? You probably remember the level of the crowd noise determined how loud you needed to talk. This is an example of a signal (your voice) to noise (the crowd) ratio. The signal-to-noise ratio can be used in electronics as well as acoustics. The comparison is usually expressed in dB (decibels). A decibel is a ratio between two levels. In a piece of electronic equipment, the signal-to-noise ratio is a comparison of the desired signal and the unwanted noise that is generated by the equipment. For example, let's look at a typical full gymnasium just prior to a pep-fest. You will probably hear a "noise floor" (or level of ambient noise) of approximately 60 dB. In order for a speaker to be understood, his/her voice (with the help of the sound system) must be at least 10 dB higher in level than the ambient noise in the room. Or put another way, the signal (voice)-to-noise ratio between the sound system output and the audience noise must be at least 10 dB. Confused? Maybe a different example will help. A cassette tape recorded on a typical cassette deck will have a nominal (normal) signal level of dBu. The u in dBu is a standard reference level. The noise floor of the tape and the cassette deck electronics is typically -68 dBu. This means that the signal-to-noise ratio is 68 dBu. | 
| ...the deck with the highest
[signal-to-noise] ratio will produce the quietest recording. | 
| You can now use this knowledge to help choose some new sound equipment. Say, for example, you want to get a new cassette recorder. Find a couple of decks with the operational features you want. Now look at the published signal-to-noise ratio in the specifications. If the equipment is measured the same, the deck with the highest ratio will produce the quietest recording (less noise or hiss). If all the other operational features are the same, the quieter deck may be your best buy. by Travis Ludwig © 1996 Internet Sound Institute (www.soundinstitute.com). This article is for personal use only. Any commercial reproduction is not permitted without permission. To obtain permission, contact ISI at hopi@soundinstitute.com
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