FFT length in SignalScope Basic

stmoeller60

Where can I define the fft length ? by example 2048 0r 4096 ? Where can I set the sample rate ? by example 44,1khz or 48khz ?

benfaber

In SignalScope X, FFT length is defined by the frequency resolution selected in the FFT Analyzer Options menu, along with the current input device's sample rate. You can adjust the device sample rate in the I/O Configuration menu (accessed by tapping the microphone icon on the left side of SignalScope X's main toolbar).

The FFT length will be the ratio of the sample rate and the frequency resolution. So, for example, if you have a sample rate of 48 kHz and a frequency resolution of 10 Hz, the FFT length will be 48000/10 = 4800.

In the interest of using 'user friendly' frequency resolution, SignalScope X employs mixed-radix FFT's, rather than strictly using powers of 2 (radix 2). (If only powers of 2 were available, the frequency resolution would be, e.g., 11.71875 Hz at a sample rate of 48000 with an FFT length of 4096.)

See SignalScope X's built-in documentation, or access it online: I/O Configuration Menu FFT Analyzer Options Menu

stmoeller60

Thanks for your answer . I can't find any possibilty to adjust the sample rate in in the I/O Configuration menu ? I'm using Iphone XR with internal mic or Zoom U22.

Unfortunatly SignalScope doesn't use powers of 2 fft length, because these are not comparable to my simulation spectra in matlab.

Does faber has another IOS App which uses powers of 2 fft length and adjustable sample rates ?

benfaber

I apologize for the confusion. The sample rate cannot be adjusted in SignalScope Basic. That requires the Advanced or Pro version. It can also be adjusted in SignalScope X, regardless of the subscription status. None of our iOS apps will currently allow you to select an FFT length that is a power of 2. Technically, it would work if you had a sample rate that is a power of 2, but I'm not aware of any audio devices that support that. Our legacy Mac apps support arbitrary FFT lengths, but although they are still available in the Mac App Store, they are no longer being actively developed. We can take a look at adding arbitrary FFT lengths to newer versions of SignalScope, but as far as I know, you're the only person to request it. Perhaps, another option would be to use different FFT lengths in your MATLAB simulations. I don't believe that the built-in FFT function is limited to powers of 2.