:<math> \exp[-(\pi f_{\delta} \tau)^2] = \exp[-(\pi \Delta f \tau)^2] = \delta
\quad \Rightarrow \quad \tau = \frac{\sqrt{-\ln\delta}}{\pi f_{max}} </math>
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:<math> \exp[ -[\pi(f_{\delta} - f_0)\tau] ^2 ] = \exp \left[ -\left(\pi \frac{\Delta f}{2} \tau\right)^2 \right] = \delta
\quad \Rightarrow \quad\tau = \frac{2\sqrt{-\ln \delta}}{\pi \Delta f} </math>
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