Definitions to Some Key Parameters of An Amplifier—S/N

S/N Signal to Noise Ratio

S/N, or SNR measures the ratio of signal power to the noise power of the audio equipment, so the higher the value is, the better the product is.

The old method measures the S/N at rated power. It results in different S/N values even products with the same internal noise levels. The presence of power causes the difference, so CTA-2006 revised the method of S/N measuring with1 watt (2V rms into 4 ohm) reference power to the amplifier. Yet the amplifiers S/N measured under the new method is less than that measured with the old method, since the additional power is removed.

For instance, an amplifier rated at 100W*4 are measured with 95dB S/N under the rated power. The S/N measured with the new method, 1W, is 75dB.

S/N (A weighted)

Neither all noise is audible to ears, nor the noise of over the full frequency band are perceived to has the same loudness by the ears, so weight is given to different frequency noise over the spectrum. A-weighted S/N is closer to describe the effect perceived by ears, and is about 10dB higher than the unweighted S/N.