The output level , when at 3:00 is -5.5dB , at 12:00 is -16dB , at 9:00 is -32dB.
Base on output level , thd+n should be like this.
With sys 9:00 volume , in % way , i think : THD+N(-30dBV output) = THD+N(Ap@2dBV) + THD+N(sys@-30dBV) , 0.0025% = 0.0002% + THD+N(sys@-30dBV) , so...