We test the sound quality of the boards with the loopback test of Rightmark Audio Analyzer. Do note: this means we test the quality of both the input and output of the on-board sound cards simultaneously. The 'weakest link' determines the result.
The dynamic range and noise level test are very comparable and show nearly identical results. The dynamic range test measures the different in volume between the loudest and softest observable signal, the noise level test measures the difference between the loudest sound and the noise level.
To put the numbers in perspective: the highest dynamic range c.q. noise level theoretically possible with 16 bit sound is 96 dB. 99.9% of the sound you listen to on your PC (CDs, MP3s, YouTube, games,...) is 16 bit and the graphs proof that the hardware is no bottleneck in almost all cases. We can only achieve the higher scores by testing with 24 bit audio. By the way, we can't imagine someone actually able to distinguish between 91 dB and 100 dB signal/noise ratio.
All motherboards with the ALC1220 codec score higher than 100 dB, however the X370GT3 unfortunately does not due to the fact that it features the older ALC887 codec. Even though the graphs might suggest something else, this isn't a bad score at all for an onboard audio codec. The differences mainly showcase how good the ALC1220 really is.
The stereo crosstalk tests to which extent sound from one channel (left or right) resounds on the other channel.
Lastly we measured the total harmonic distortion, the average distortion in the frequency domain, using RMAA.