Hey guys, I just tried to record a simple osc~ 80 Hz in a wav file.
When I open the file in sonic visualiser to get the spectrogram I wasn't expecting it to be like this but to clearly show a red line at 80Hz and nothing else..? What am I missing? Spectrogram attached.
Thanks

@leech If you reduce the dynamic range of the spectrogram, or increase the resolution, or both, you can get it to show a line at 80Hz.
40dB and about 16384 bins should give you a red line with standard colours.
Although a sine wave has a constant frequency the rate of change of amplitude varies over the cycle.
Windowing functions are used with FFTs. These transform the signal block-by-block into a spectral representation whose resolution (accuracy) in both the frequency and time domains are proportional to their size.
Unless the window "width" ...... time....... matches the width of a cycle or cycles of the sine wave you will get spectral leakage.
http://download.ni.com/evaluation/pxi/Understanding FFTs and Windowing.pdf
David.

thank you for the reply and for the document