# QA402 “Wear” Maybe? **URL:** \ **Category:** Uncategorized\ **Created:** [May 23, 2022, 11:04pm UTC](https://forum.quantasylum.com/t/qa402-wear-maybe/691 "2022-05-23T23:04:11Z")\ **Posts on this page:** 1\ **Showing post:** 14
**Author:** ![matt](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@matt](https://forum.quantasylum.com/u/matt)\ **Post date:** [June 5, 2022, 3:20pm UTC](https://forum.quantasylum.com/t/qa402-wear-maybe/691/14 "2022-06-05T15:20:02Z")
Hi @Moto, your unit is working as expected. In the link below, see the discussion on whether the DAC is being set to optimize for THD or optimize for THD+N. They are different settings and these aren’t adjustable by the user, although they might be at some point down the road. In short, to optimize for THDN loopback, you’d want to have the software adjust the relays and run the DAC very close to full-scale output… And if you optimize for THD, you want to have the software adjust the relays and run the DAC about 15-20 dB away from full scale. So, if you specify 0 dBV full scale output, and you wanted to optimize for THD, you’d set the DAC attenuators to 0 dB (18 dBV full scale output) and then send a -18 dBFS output stream to the DAC. If you wanted to opimtize for THDN, you’d set the full scale output to 8 dBV, and send a -8 dBFS output stream to the DAC. This assumes you have full manual control, which isn’t an actual option. > [@Sneak Peek: The QA402](https://forum.quantasylum.com/t/sneak-peek-the-qa402/203/79): > > Hi @ChUml, Below is a representative plot of THD. Below is a representative plot of THD+N Compared to what was previously posted you can see a lot of clean-up around discontinuities. This is from smarter switching points for the relays. For loopback, here is THD And for loopback, here is THD+N One issue is that the input and output relays need to be configured differently depending on whether you are wanting to optimize for THD or THD+N. For best THD… --- _[View the full topic](https://forum.quantasylum.com/t/qa402-wear-maybe/691)._