[Jack-Devel] audioadapter: quality setting important when not changing sampling frequency?

[Chris Caudle]

On Fri, September 28, 2018 1:51 pm, Holger Marzen wrote:
> I cannot to further examination because the spectrum analyzer in
> Audacity can't show the harmonics accurately. I expect a single peak in
> a sine wave's spectrum but I got a softer curve.

You cannot perform FFT on an arbitrary length of data, it must be power of
2.  Because of that most applications will use a window which is
essentially a multiplication in the time domain with an envelope to force
data to 0 at the beginning and end of the time series to enforce no
discontinuities.  If you pick your number of samples to be a power of 2
with an integer number of cycles for your test signal you can get away
with no window function, but for an arbitrary signal you must use a window
function (rather the trade off is a large amount of distortion shown
because of signal truncation if you use no window, or a slight spreading
of the signal energy if you use a proper window).
Longer data sets (larger number of FFT points) should result in less
energy spreading in the frequency domain.

-- 
Chris Caudle