The flat top window has the best amplitude accuracy of all the smoothing windows at ±0.02 dB for signals exactly between integral cycles. Because the flat top window has a wide main lobe, it has poor frequency resolution. The following equation defines the flat top window.
| where | ω = 2πn/N |
| a0 = 0.215578948 | |
| a1 = 0.416631580 | |
| a2 = 0.277263158 | |
| a3 = 0.083578947 | |
| a4 = 0.006947368 |
The following figure shows a flat top window.
The flat top window is most useful in accurately measuring the amplitude of single frequency components with little nearby spectral energy in the signal.