Originally Posted by jaddie
Not true. It can result in many different improvements in a noise measurement depending on noise spectrum...which is the point of a weighting network.
After digging around on the quantesylum site, I could find no background information for the test image above. If there is some somewhere, please post a link.
Interesting statement. How are you "measuring" these figures? Are you actually generating some form of distortion or are you trying to simulate harmonic distortion by summing sine waves at different frequencies and levels?
Take a look at TI or Cirrus ADC data and you'll see A Weighting is always 3 dB better than unweighted. Yes, if your noise floor is hugely distorted that rule won't hold. If your signal of interest isn't 1 KHz that rule won't hold. But for flat noise with a 1 KHz test tone, it's 3 dB.
See the section "Noise Floor" on the page below. The noise floor of an MP3 is substantially higher than a 24-bit file format. If this graph is true, then it'll readily be audible.
For measuring which THD figures I can hear, it's pretty simple to just generate a 1 KHz tone, and then add in a 2, 3, 4, 5, KHz tone at an increased volume and note at which point you can hear the added tone. Try it and report back. It's really hard to hear 2nd and 3rd order distortion, and much much easier to hear 7th order.