1. Sound quality

In ePSXe, you can set full effects (high quality), partial effects or disable the audio ouput. Disabling the audio will speed up emulation but some games could stop working. High quality have more sounds effects (interpolation, reverb, filtering), but more cpu is required, if you have a fast phone eanble high quality to hear the 100% of the PSX sounds (it is required in some games such Vib Ribbon or Parappa the Rapper).

2. Sound Latency

You can use the normal latency mode, avaliable from the first version, the low latency mode (experimental - frecuency is adjusted to emulation speed, but you need 100% fps to get good sound), or the new low latency experimental mode 2 (recommend if you want a very accurate sync between video and sound effects), which doesn't adjust the frecuency.