Signal to the Noise Ratio

Signal to noise ratio (SNR or S/N) is a gauge or measure of the signal strength comparative to the noise in the background. The ratio measurement used is decibels (dB).

The Facts

In simple terms, SNR is the difference of the reference level and the noise floor. The reference level is made by the individual conducting the measurements.

With amplifiers, the reference can be one watt into a particular load, a volt, full power or any of the other settings. To conduct comparisons between the two components examined with differing methods, the reference used must be determined.

Some are under the assumption that electronic equipment (i.e., amplifier, equalizer etc) with a high S/N ratio is superior to one with a lower S/N ratio. However, this is not always the case as the following example will show.

Ratios up Close

Suppose there are two amplifiers. One has an S/N ratio of 102dB and the other 80dB. Some would think that the amp with the higher ratio is less noisy. Assume that both amps have a rating of 600 watts.

Presuming that the amp with the higher ratio has been tested at full power and the one with the lower signal to noise ratio has a rating of a single watt. You can determine the decibel difference of 1 watt and 600 watts with this formula: dB=10*log (value1/value2).

dB = 10*log(value1/value2)

dB = 10*log(600/1)

dB = 27.78

The difference is 27.78dB. To make the appropriate comparison, deduct 27.78 from 102dB. The ratio is 74.22dB. The result is a 74.22dB for the amp with the higher ratio. This is obtained when the reference is altered from full power to a single watt. When the same reference is used, the amp with the lower ratio is actually less noisy.

SNR for Cable Modems

When it comes to Net connections, the SNR have to be 30dB at least. Using higher settings is preferred. The limit for majority of cable modems is about 40dB.

However, a 30dB or higher setting does not automatically mean quality connections. The signal power is another factor that can affect the transmission. If the dB is under 30, interruptions will likely occur. There are of course, other possible reasons why connections will fail.

Some of the technical aspects of the signal to noise ratio may be difficult to understand. However, they are very important especially for those who demand the highest quality sound from their speakers and modems.

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