Improving the quality of an optical audio transmitter
I'll just point out one contributor to your audio distortion:



Figure 1. Extract from the PGM 5506 datasheet.

You didn't supply a link to your LDR datasheet but it's probably similar to the one above. As you can see the response times are in tens of milliseconds so at best they can only respond reasonably well to about 20 Hz. Anything above that will be "slew-rate limited" meaning that a step change in light intensity will give a response much like a resistor-capacitor (RC) charge / discharge curve.



Figure 2. RC charge / discharge curves for a squarewave input signal. Source: EEEGuide1. The LDR will give a similar response although the lower trace may be inverted depending on how you've wired it to the receiver input.

You might need to advance to a photo-transistor or photo-diode solution.

One other thing: you should have a DC decoupling capacitor between your receiver and the mic input of your laptop. This will remove any DC component and may prolong the life of your laptop.