Audio Precision SNR

audiosnr

I recently checked SNR of the class D Amplifier on board our product. I used AP2722 for amplifier characterization. The SNR displayed by the analyzer as below:

-87.85 db below 2.76 dbV reference level at 0.08 % THD + N

I am unable to understand this. Is this good or bad?

Best Answer

87.85 db below 2.76 dbV reference level at 0.08 % THD + N

Let's start with the 2.76 dBV - this is the voltage level measured by the analyzer and is a sinewave of ~1.374 Vrms plus a bit of noise and distortion. This I believe is what the analyzer is measuring at your amplifier's output i.e. it is the total of: -

  • Output sinewave (at some frequency possibly 1 kHz) +
  • Noise +
  • Distortion

The SNR is quoted as 87.85 dB below the ~1.374 Vrms = ~55.7 uV.

0.08% THD + N relates to the ~1.374 Vrms and this is 1.1 mV.

Given that noise is 0.0557mV, the distortion on its own comes out at still pretty close to 1.1 mV.

Hopefully that helps the understanding and, as far as I can tell, it's "pretty good" but that is a subjective term - if the frequency were 10 kHz I'd say it's really good especially if the output voltage level were close to the full range of the amplifier's output AND under full load conditions. Given that you haven't stated either it's really anyone's guess as to how subjectively good or bad it is.