I am considering buying a QA403 but I have a couple of questions I cannot seem to find an answer to.
First does the input bandwidth follow the sample rate. In other words at 192KHz sample rate can I measure signal up to 96KHz and display them or is the bandwidth limited to 20KHz no matter what the sample rate.
Secondly, I see all the example displays show levels in dBV. I am measuring pro audio equipment and we measure everything in dBu. Can the display be switched to show dBu?
Cheers
Ian
Hi Ian, the answer in “yes” on both. I almost always use 96kHz bandwidth and dBu. On top of that, you can manually specify the required bandwidth. So, you might want to measure THD+N from 20Hz to 20kHz even if the SR is at 192kHz.
Thank you for your answer. I found the dBu setting by RTFM but I am still not sure about the bandwidth. I agree you might only want to measure THD from 20Hz to 20KHz but to measure 20KHz distortion the analog bandwidth needs to extend to 80KHz just to be able so see up to the 4th harmonic (as weel as having a 192KHz SR). What I am unsure about is if the analog input circuits of the QA403 have an analog bandwidth this wide. Where is this written down? I cannot seem to find it. There needs to be some kind of filter to prevent aliasing but it is not clear to me if this scales directly with SR.
Cheers
Ian
I did a quick response test sampling at 192K and the signal was down about .25dB at 50KHz and .75dB at 90KHz after which it started dropping rapidly. It looks like a digital wall filter and any distortion values will be pretty accurate up to 20KHz.
Mark