Praxis software - how do I set the LF cutoff frequency?

[gentlevoice]

Hello DIYs',

I am in the process of getting to know the Liberty Instruments' Praxis software for measuring THD, FFT, frequency response, phase etc.

However, when I use the spectrum RTA 1 Channel acquisition I cannot make the software go below approximately 300 Hz in the measurement screen, although it is supposed to go down to 1 Hz, as set by the start frequency setting (see attached screen dump). I need to be able to go below 1 Hz (and up to around 100 kHz).

Any of you know this software and have suggestions as to how I do this? Also, if any of you have suggestions for other softwares that can measure these parameters I'd appreciate your feedback.

Need be not too expensive (free or < 100 USD).

Thanks, Jesper

[bwaslo]

Increase the FFT size. Lowest resolvable frequency hast to be higher than samplerate/FFTsize (you can't know the 1Hz response with less than 1/1Hz of time analyzed.

[gentlevoice]

Thanks for the tip - it works! It also makes the screen updates slower (because it needs to sample many more times to obtain data for the window size?) but now I find it really useful.

Maybe you are familiar with this software?

Anyway - many thanks

Jesper