1. Please check that you have installed the latest drivers of your sound card from manufacturer.
2. For SBLive card:
Please choose CustomSettings in il2setup and make sure that the checkbox 'disable hardware voice manager' is checked.
3. If it does not help, please try to set in il2setup Settings->'No hardware
acceleration - Win98/ME'. (Or Win2000 if you have this OS)
4. Also, please choose CustomSettings in il2setup and make sure that the number of playback channels is no less than 16, which is an optimal setting.
It makes sense to choose less than 16 channels only if your sound system dramatically slows down gameplay.
5. If you still experience slow playback, please check that the “Control Panel->Sounds and multimedia->Audio->Sound playback->Advanced->Performance->Sampling rate converion quality” slidebar is set to the utmost left position (please also have a look in manual)