I. Introduction
People with hearing loss suffer not only from an elevated threshold for detecting sounds but also from understanding speech, especially in noisy environments [1]. One of the ef-fective approaches to address hearing loss is the use of hearing aids. Hearing aids amplify the acoustic signals and send the amplified signals into the ear canal. The signal is amplified frequency-dependently and the amount of amplification at each frequency region is appropriately determined by the degree of the user's hearing loss in each frequency region [2]–[4]. This process significantly improves speech understanding in quiet environments [5]. However, when background noise is present, both the speech and the noise are amplified, and users with cochlear hearing loss cannot understand speech as effectively as prople with [1]. Therefore, nowadays, most commercially available hearing aids have speech enhancement systems, and there have been many studies on speech enhancement [6]–[9].