# Newbie with a question on QA403 precision **URL:** \ **Category:** QA40x\ **Created:** [June 16, 2023, 1:44am UTC](https://forum.quantasylum.com/t/newbie-with-a-question-on-qa403-precision/910 "2023-06-16T01:44:15Z")\ **Posts on this page:** 1\ **Showing post:** 2
**Author:** ![matt](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@matt](https://forum.quantasylum.com/u/matt)\ **Post date:** [June 16, 2023, 2:34am UTC](https://forum.quantasylum.com/t/newbie-with-a-question-on-qa403-precision/910/2 "2023-06-16T02:34:18Z")
Hi @gallantus, generally to accurately measured THD+N, you need need a measuring device with ~10 dB better THD+N than the device you want to measure. The best THD+N from a DAC these days is around -121 dB or so, which suggests you need a measuring device with about -130 dB or so. But, those don’t exist. So, the best you can really do is confirm it’s getting close. Next, you can use a notch to improve things further. A good thread on attempting to measure the E70 Velvet is below. This should help you understand the limits. > [@Topping E70 Measurement vs QA480](https://forum.quantasylum.com/t/topping-e70-measurement-vs-qa480/790): > > @matt I just got a Topping E70 and started to do some measurements on it. Looking at Audioscience Review and others, the 1Khz numbers are around -123db thd+n and thd close to -140db. I tested the E70 directly into a Cosmos ADC at -135db thd and -122.9db thd+n at 5vrms out. I wanted to see what things would look like on the QA402 and went back to the specs doc on your site for the QA. There is page there titled Plot:THD+N Spectrum from External Source where you are using the oscillator from th… --- _[View the full topic](https://forum.quantasylum.com/t/newbie-with-a-question-on-qa403-precision/910)._