Externalization ratings: actual data from psychoacoustic experiments (closed circles) and simulations of the single-cue models (open symbols). (a) Effects of low-frequency modifications tested by Hartmann and Wittenberg [33]. Exp. I: IID set to zero (bilateral average magnitude); actual data from their Figure 7, average from N = 2. Exp. II: ipsilateral magnitudes flattened (IID compensated by contralateral magnitudes); actual data from their Figure 8, average from N = 4. Simulated results for various cues, average from N = 21. (b) Exp. III: effect of spectral smoothing of low-frequency sounds presented from various azimuths (left: 0°; right: 50°); actual data represents direct-sound condition from Hassager et al. [17], average from N = 7. Simulated N = 21. (c) Exp. IV: effect of spectral smoothing in high frequencies as a function of spectral contrast (C = 1: natural listener-specific spectral profile; C = 0: flat spectra); actual data calculated from the paired-comparison data from Baumgartner et al. [34], N = 10 (actual and simulated). (d) Exp. V: effects of stimulus bandwidth and microphone casing for various mixes between simulations based on listener-specific BRIRs (100%) and time-delay stereophony (0%); actual data from Boyd et al. [35], N = 3 (actual and simulated). ITE: in-the-ear casing; BTE: behind-the-ear casing; BB: broadband stimulus; LP: low-pass filtered at 6.5 kHz; Error bars denote standard errors of the mean.