Thanks, yes you are right buffer sizing is serious issue in the FFT, but there are methods to deal with it. For example if you have buff size 441 as you described, and you just want to plot on screen the chart of freq, you can make nice radix2 fft on 512 samples where 441 samples would be your samoles and for the rest 71 samples just take zeros. It called Zeros Padding. But as I told it’s not a problem here, my fft do all those conversions automaticaly, so I don’t need to worry about buffer size at that point.