I know normal FFT with a fixed window size will introduce leakage and rectangular window function will give me the best main lobe width.
For example, with 44100Hz sample rate, 2048 window size, a 64Hz sine wave will have about 20~30Hz resolution in a VST plugin called Voxengo SPAN.
However, in Image-Line Wave Candy and Edison, with the same configuration (44100Hz sample rate, 2048 window size), it can have nearly 1Hz resolution. (I'm not sure Image-Line plugins use FFT but I can confirm Voxengo's uses FFT because they stated in their documents)
My question is how to achieve the spectrum resolution like Image-Line's plugins without increasing window size (limited by time resolution) or sample rate? Whether with DFT-based algorithm or other algorithms. The input signal is audio signal (20Hz-20kHz). It is not always sine wave. It could be polyphonic and complicated waveforms.
From @Dan Boschen's suggestion I tried to place two sine wave as close as possible before aliasing. It seems it is not really 1Hz resolution. (about 15Hz minimal I can get before this happens visually)
Although it is not 1Hz resolution, their result is still what I want to achieve. So I will try zero padding later.