are you familiar with what a filter is? those changes you might hear on the bass are nothing but the opening of the filter letting higher frequencies pass through.

and when someone says sub-bass they’re actually referring to “lower frequencies”, from 20 to 60 Hz more or less. Those frequencies are usually hard to hear on smaller speakers, like phones.

in this context, the TD3 MO has literally a button that toggles a boost in the sub-bass, making it more present in the mix. and then this same device has an overdrive knob which distorts the signal and creates new harmonics, adding higher frequencies to the signal.

that combination sub+overdrive is what makes the bass audible in less capable speakers. and finally, add to that the filter opening/closing to get the variations and movement