## 1 Introduction
### Aim of the Study  
The abovementioned previous studies provide useful practical implications on 3D sound recording and mixing. In terms of 3D microphone array design, the height layer microphones should first be of a directional polar pattern (e.g., cardioid or supercardioid) and angled upwards, so that the level of VIC would be at least \(-\)7 dB, relative to the direct sound in the main layer microphones. This VLT can also be a useful reference when a sound engineer aims to vertically pan a phantom image to the main layer position in 3D sound mixing. It is also evident from [10] that a similar amount of ICLD would also cause a phantom image to be fully panned to the physical position of the height layer. In such methods, the amplitude of the signal in the height layer is reduced as a whole (i.e., even attenuation across the frequency spectrum). Henceforth, this method will be referred to as 'blanket VLT'.  
However, in [7; 8], VLT was also found to have a significant frequency dependency for octave-band noise stimuli, being associated with psychoacoustic phenomena, such as the 'pitch-height' effect [11; 12; 13] and the directional bands [14]. In general, the bands centred at 1 kHz and above generally having lower threshold than the lower bands (e.g., \(-\)7 dB for the 250 Hz band and \(-\)13.5 dB for the 8 kHz band). This formed the initial hypothesis of the current study that the VLT could be applied in a band-dependent manner, rather than as the blanket. The rational for is as follows. As [PERSON] [3] found, the application of VLT does not totally mask the perceived effects of VIC, such as the increase in vertical image spread and tone colouration; further attenuation of VIC is required to achieve a total masking (i.e., VIC being completely inaudible). However, in practical 3D sound recording, mixing, and upmixing applications, such spatial and timbral effects may be found to be preferable, as found in the case of horizontal interchannel crosstalk [15]. Therefore, by applying the band-limited or single band VLT method,the spatial and tonal benefits would be preserved, whilst ensuring the desired vertical image position. Furthermore, many professional recording engineers prefer using omni-directional microphones rather than directional ones for the height channels [16; 17], even though they are more prone to the undesired vertical localisation shift due to the high level of VIC that is presented in the height channel signals. This seems to be mainly because of their fuller and more spacious characteristics of sound benefitted from the extended lower frequencies and the greater ICTD between direct sounds. In such a case, VIC could be reduced only for specific band(s) in post-processing to avoid the vertical localisation shift issue with minimal influence on the perceived spatial and tonal characteristics. This leads to the following research question for the present study: Is it possible to achieve the goal of avoiding the localisation interference effect of VIC by applying VLTs for a limited frequency range or a single band instead of the blanket VLT method?  
The rest of the paper is organised, as follows. The design of the subjective experiment conducted is first described. Statistical analyses of the data obtained from the experiment are presented in Section 3. Following this, discussion on the results and their practical implications are provided in Section 4. Finally, Section 5 concludes the paper.