Has anyone used Siglib? Answer a question on the FFTr function?

Question

I'm hoping someone - anyone can answer a question on the Siglib library call to perform an FFT on data.

There's no examples anywhere I can find that provide a real application using data from an ADC, so that's where my wheels are spinning. The examples from Numerix have only canned data, generated by the function SDA_SignalGenerate. Specifically, in the FFT example, SDA_SignalGenerate is passed a value of $0.15625$ for frequency. Can anyone provide some insight as to what this represents? The FFT_LENGTH of the FFT function is $512$, but I do not see what the SDA_SignalGenerate frequency of $0.15625$ means, or what it is normalized to.

Thanks for any help anyone can provide.

Answer 1

This is the frequency normalized by the sampling frequency, i.e. in your case the frequency in Hz is

$$f=0.15625\cdot f_s$$

where $f_s$ is the sampling frequency in Hz. This can also be found in the SigLib reference manual (p. 251).

Answer 2

First off, my apologies for not replying before now but I didn't realize there were any SigLib questions on here. I know it has been a long time but I don't like threads that I should respond to to be left unanswered. I'm sure you've moved on by now but I figured there is no harm in answering your question.

Matt is absolutely correct but further to this, the way I like to think about this is that the SigLib functions use a normalized sample rate of 1.0 Hz. Further details are in the SigLib Overview section of the User's Guide.

If you need any further assistance then please do not hesitate to contact me through the Numerix-DSP website. Best regards, John