In the current version of the software for the QA403/QA404, what is the max sample rate that can be used for external DAC testing? Most of the DACs that I’d like to test are 24-bit and go up to 384 kHz.
Hi @bryman79, 192Ksps is the max supported by the software and hardware. However, there is a 384Ksps “experimental” mode in the software (enabled by the -384k command line option) where the ADC should run at 384Ksps.I’d not consider the -384k mode super reliable, but for a quick check it can do fine.
Here’s a Topping E70 Velvet forced into 32-bit 384Ksps in Windows, with the QA40x app launched using the -384k command line option. That enables the 384K sample rate button to be pressed. Note that the analyzer DAC is delivering random junk in this setting, so don’t have anything connected to the DAC outputs. And here’s the plot out to 200kHz shown below. You need a notch to unlock the measurement down to -125 dB THD+N or so. As you can see from the plot, mirror mode is working at 384K, along with acquisitions.
And here’s the same plot with the analyzer inputs shorted so you can see the residual noise of the analyzer.
Comparing these two, we can see the Topping E70 Velvet appears to have a bit of hash up around 150 kHz that isn’t there when the analyzer inputs are shorted.
How about sample rates from the other sample rate family? Such as 44.1 kHz and 352.8 kHz?
Hi @bryman79, the only sample rates supported are 48, 96, 192 and (experimentally) the 384.
While a lot of DACs and ADCs can support both via a PLL, the frequencies generally require a dedicated crystal to get the most out of the part. So, you either pick 44.1 and multiples thereof, or 48 and multiples thereof.