# QA403 giving DAC underrun errors and ADC overruns

**URL:** <https://forum.quantasylum.com/t/qa403-giving-dac-underrun-errors-and-adc-overruns/870>\
**Category:** QA40x\
**Created:** [April 29, 2023, 2:33am UTC](https://forum.quantasylum.com/t/qa403-giving-dac-underrun-errors-and-adc-overruns/870 "2023-04-29T02:33:54Z")\
**Posts on this page:** 1\
**Showing post:** 10

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**Author:** ![matt](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@matt](https://forum.quantasylum.com/u/matt)\
**Post date:** [May 4, 2023, 2:26pm UTC](https://forum.quantasylum.com/t/qa403-giving-dac-underrun-errors-and-adc-overruns/870/10 "2023-05-04T14:26:15Z")

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Hi @mhuth1776,

I think there are two issues here that hopefully aren’t overlapping. The link below goes through some things that need to be done when looking at THD and low frequencies. Some have been fixed, but it’s a good overview of the math and how low frequencies need a bit more attention.

Second, can you please try this:

1. Set up for left-channel loopback for L+, and short L- input
2. Set File-\>New Settings
3. Go to Gen1 and disable round to eliminate leakage
4. Set 0 dBV full scale input
5. Select the AmpThdVersusFrequency Automated Test and setup as follows:

 ![image](https://canada1.discourse-cdn.com/flex032/uploads/quantasylum/original/2X/d/ddd923f216bae8034d988323c442fdce57340163.png)

This will run 1000 cycles. While running, use your machine as you normally would–videos, downloads, etc

Here’s the plot I get at 48K:

 ![image](https://canada1.discourse-cdn.com/flex032/uploads/quantasylum/original/2X/6/6b20c98fd51920ff5b4c3dd09113811160a1d296.png)

And then I changed the sample rate to 192 and press F3 to run the test again:

 ![image](https://canada1.discourse-cdn.com/flex032/uploads/quantasylum/original/2X/a/a0439ab6c820a33c064ac806955f3e2e095272a3.png)

Can you run this on your machine and share what you get?

> [@QA401 Low Frequency Measurements](https://forum.quantasylum.com/t/qa401-low-frequency-measurements/39):
>
> A customer writes with an issue related to amplitude errors they are seeing on frequency sweeps below 100 Hz. These can manifest as wildly wrong gain values. These are most often related to FFT size and/or window choice in some way. But a change will be made in 1.830 to help with the issue too. The “AMP Frequency Response” plug-in was used to plot the gain of the QA401 in loopback mode, from 2 Hz to 100 Hz, log step, at 5 points per octave (this was at 48K sample rate with Hann windowing). Thes…

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