Wow! All the way down to 10 Hz! ![ThumbsUp :-+](https://www.eevblog.com/forum/Smileys/default/icon_smile_thumbsup.gif)
Is 500 kHz the upper limit for the AD5933?
With internal 16.776MHz clock it will do down to about 10kHz, below that it will no longer capture a full wave. But with a variable external clock signal it's no problem getting down to 10Hz .
It does take a slightly more elaborate algorithm to scan the lower frequencies, something like: set the clock to desired frequency (I use mcu PWM as clock for the lower frequencies) to capture at least 1 full wave for the 1024 point DFT, then scan 1 octave and repeat.
Downside is that it's pretty slow at low frequencies, as it needs to lock on a few waves first. But speed is not really high priority, beyond faster is preferred
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/smiley.gif)
The official, linear until, upper frequency is 100kHz as far as I remember, but it will do up to 500kHz with a roll off that starts around 200kHz. I can compensate for the roll off above 200kHz, with some loss of resolution.
I have considered trying e.g. a 20MHz external clock just to see if it will still run reliably
![Evil >:D](https://www.eevblog.com/forum/Smileys/default/evil.gif)