Input level precisions & user weighing file

[Stuartmp74]

Hi matt.

I hope that you are well and this pandemic is not affecting business to much for you.

I have a few questions if you don’t mind.

First Question.
Is the development of the QA 401 software still continuing?

Second Question.
Is it possible to increase the RMS L: & RMS R: input level display to, two decimal places just as the Peak L: & Peak R: output level measurements are? Its a real pain only having one decimal place on the input RMS level. If you can tweak this I would really appreciate it.

Question 3
Were is the best place to read about setting up a user weighing file?
I have tried creating one and I don’t seam to be getting the results as expected and explained in the context help dialog box.

What I am trying to do is reduce some of the harmonics that are shown in a loopback test of the QA401. For example. My noise floor is at ~ -135dBv and I am running a 1khz loopback test. I see that I have a second harmonic at 2khz at a level of ~ -115dBv so I’d like to create a user weighing text file to remove this…

I have tried creating one and entering 2000, -20
But that doesn’t seam to work.
I would really appreciate it if you can give me some guidance on how to use this feature and achieve the results I’m after.

All the best
Stuart

[matt]

Hi @Stuartmp74,

The QA401 software development has come to a stop, but that’s because the QA401 hardware will shortly use the QA40x software.

The QA40x software has the additional precision you want. Hopefully the cutover will be soon.

The weighting files are discussed around page 35 in the manual.

For your example of removing something at 2 kHz, let’s say you have this (note I’m intentionally overdriving the QA401 here to get the 2H way up):

And with a user weighting file below:

20, 0
1900, 0
1901, 20
2099, 20
2100, 0
20000, 0

I get the following:

So, what is the weighting file doing? It’s saying "Between the frequencies 20 and 1900 Hz, apply a correction of 0 dB to the data. And between 1900 and 1901 Hz, apply a linear attenuation ramp so that 1900 Hz has 0 dB attenuation and 1901 Hz as 20 dB attenuation. This also means that 1900.5 Hz will have 10 dB of attenuation (since it is the mid point). And the range of frequencies from 1901 to 2099 will be uniformly attenuated. And from 2099 to 2100 there’s another ramp, and then from 2100 to 20k there’s no adjustment made.

I think the confusing part to understand is that you must specify a range of frequencies, and across that range your start and end attenuations will be linearly interpolated.

Let me know if you can tweak the above to make it work for you.

[Stuartmp74]

Thanks Matt.
One other feature that would be good to see working is if you increase or decrease amplitude or frequency using the up and down arrows during a test the averaging is reset