Head-related transfer functions (HRTFs) are essential for binaural reproduction over headphones and modern 3-D audio systems such as Crosstalk-Cancellation (CTC). Distinct peaks and notches are a main factor of coloration in perceived sound when it comes to mismatched HRTFs, e.g. when using artificial head HRTFs. As a countermeasure, smoothing algorithms are used to reduce this effect. Strong smoothing however results in poor localization performance as crucial cues vanish. To find the best trade-off the just noticeable difference of smoothed HRTFs are determined direction-dependent in an expert listening test using individual HRTFs and headphone transfer function compensation.