Hi tecden23,
The oscillator used in the bass drum circuit does of the pulsar-23 does not track 1V per octave like the bass synth oscillator, so it will not follow a keyboard the same way as the bass synth.
For a true sub octave, you would need to use an external oscillator that tracks 1V per octave to follow the bass synth, but I’ve also had some interesting results sending the bass synth to the Delay in PCH mode and setting all the knobs fully counter clockwise, except DLY OUT which I set fully clockwise. This causes the delay to generate a pitch that is an octave down from the incoming signal.