Alder. Alder is light in weight with soft tight pores like Basswood. But there is a large swirling grain pattern to it with harder rings and sections. So imagine a Basswood type texture but with harder rings peppered throughout. That adds to the stiffness, and the complexity of the tones. It retains more of the highs that Basswood softens, but also gives some room to the lows. You have a broader spectrum of tones, which leads to the perception of a little less mids than Basswood.
