The QA401A from quant asylum ( is basically a USB soundcard pimped to the requirements of audio testing. It differs from typical soundcards by the BNC connectors of the balanced In- and Outputs, which are of course also useable in singleended fashion. A -20dB attenuator is also integrated.

The In- and Outputs are designed carefully to not compromise the dynamic performance of the AD- and DA-converters.

The supply via USB and its compact casing allow for mobile useage, though it limits the allowed signal voltage range and the dynamics. Utilizing a more refined supply with higher rails one could expect a couple of dB lower noise floor, but this is of rather academic than practical value. Not least could You gain some dBs here and there by using dedicated external signal amplifiers (Microfone-preamplifier, super-lownoise preamplifier).

The QA401a comes with a software package that contains most of the typical audio measurements, that makes handling really easy and which fulfills almost profeesional requirements. A newer software supplement named Tractor allows the control and interaction with the matching electronic load QA450 for automated testing and characterization of the DUT.

At 450US$ it is a neat little device, still within the budget of ambitioned DIYers, but also well useable for professionals.