# Listeners' Spectral Reallocation Preferences for Speech in Noise
## 4 Expt. 2: Spectral Reallocation Preferences for Band-Limited Speech
### Interim Discussion  
When given the ability to control the cut-off frequency of low-pass and high-pass filtered speech, listeners' most frequent choice was for values that led to the widest possible speech bandwidth (Figure 6), although this was by no means a universal preference (Figure 5). A similar finding was observed when listeners controlled the bandwidth of speech directly. For the HP and BW conditions, listeners were able to achieve similar intelligibility rates over a wide range of bandwidths. This can be explained on the basis of the existence of audible speech glimpses in the region above 1 kHz across a range of parameter values (Figure 7) for the HP and BW conditions; conversely, the LP and CF conditions indicate an absence of adjustment latitude if the goal is to maintain mid-high frequency speech. Our findings for the HP condition also align with the results reported by [PERSON] and [PERSON] [44], who employed machine learning techniques and an intelligibility model to determine appropriate spectral weightings. Their study found that enhancing frequencies above 1 kHz was optimal for improving speech intelligibility in the SSN condition at \(-6\) dB SNR, consistent with the findings in our study. Additionally, both studies observed a similar trend concerning the optimal frequency range for the different SNRs. Specifically, for lower SNR, there was a preference for a greater cut-off frequency.  
The finding that listeners preferred to increase the high-pass cut-off frequency by around 50% in noise is unexpected but explicable on the basis of trading off energy in the sub- and supra-1 kHz regions. The relative unimportance for message decoding of the sub-1 kHz frequency region is consistent with the observation that talkers, when confronted by high-pass filtered noise, also increase energy in the mid-frequency region rather than attempting to exploit the (unmasked) lower frequency zone [80].  
In the more adverse masking conditions, listeners appeared to trade off bandwidth increases against the availability of audible speech in important frequency regions. This search for a compromise is most evident in the HP and BW manipulation conditions. Listeners sacrificed frequency components below 1 kHz (LP/BW modifications) and above 4 kHz (HP/BW modifications), leading to the boosting of the mid-frequencies.  
Figure 7: Proportion of glimpses in each spectral region as a function of listeners’ adjustment preferences. Vertical bars indicates mean listener preferences. Details in Figure 4.  
In noise-free conditions, listeners chose an octave band of speech centred on about 1.4 kHz. Our work extends [PERSON] et al. [79] (Expt. 1), who measured intelligibility for low-predictability SPIN sentences [81] in six different 1-octave bands, finding the highest score of approximately 55% for a band centred on 2 kHz, and the next highest score of 40% for the 1 kHz band. Our findings suggest that intelligibility is rather sensitive to the choice of centre frequency: selecting bands centred on 1 or 2 kHz leads to a substantial drop in scores (top right panel of Figure 6).