Maximum THD testing frequency

QA401
1

Hi All,

I was doing some distortion testing on the weekend and was only able to take measurements up to 6.5khz

Is this normal and if so why is it so low?

My previous testing platform which was a Scarlett 2I4 audio interface and I unsed multi instrument as the testing software.

I used to test up to 16Khz as this gave me 6 harmonics out to 97Khz.

download_20200922_071411
download_20200922_0714114032×2268 3.61 MB

Also attached is a plot of multi instrument at 15.999Khz

20200922_111653
20200922_1116531134×2016 1.01 MB

2

Hi @Stuartmp74, in the THD options, you need to set the measurement stop frequency to the highest harmonic you wish to capture (keeping Nyquist in mind)

image

3

Thanks, @matt its working. I hadn’t check that context menu before.

4

Hi @matt, upon further investigation it appears that the AMP THD Versus Frequency dialogue box does not allow values over 20,000 hz

Am I doing something wrong again?

20200923_074654
20200923_0746542268×4032 3.85 MB

I was about to change it to 95999 hz in the THD context menu as discussed previously

20200923_074524
20200923_0745242268×4032 3.64 MB

It would also be great if we could have a lower minimum increment that 1 dB

20200923_075350
20200923_0753501134×2016 1.08 MB

5

Currently, all the plugins must assume 48K sample rate. There’s no way for a plugin to query the user sample rate that has been selected. And so, there’s no way to error check. Maybe that could be changed easily, I’ll check.

I’ve entered the issue on github