If you want to do portamento - "sliding notes" using HPWM and Picbasic pro, you should do it with ASM, because, PBP on each HPWM statement, resets and restarts PWM generator, which sounds additional bzzzzzzzz, while doing portamento.

If you really want to go deep into music with PIC, you should try LT8500 IC - this is 48 channel 12 bit PWM generator with fine adjustments - you can have impressive 48 voice polyphony, or say 24 voice with 2 operators per channel, or 12 with 4 operators and so on.