Created preliminary circuit for isolating the sub-bass frequencies from the headphone port, here represented by V1

The first part of the circuit is the inverting amplifier.  It amplifies the raw voltage from the headphone jack.  As of now this will be common for the entire music visualizer circuit.

The second part is the low pass filter, the cut of frequency is about 60Hz.  Because this is a single pole filter it attenuates the signal at -20dB/decade, this is too slow as it doesn't attenuate the Bass frequencies enough, will have to use a higher order filter.

The last part of the circuit is the voltage rectifier.  The first part of the rectifier is the voltage follower, it isolates the LPF from the bridge rectifier, therefore the bridge rectifier doesn't affect the frequency response of the LPF.

Below shows Magnitude Bode plot form 1 to 100Hz

Below is transient response with a sine of 10Hz and an amplitude of 0.17V