Do you have some older program which uses /dev/dsp device? It no longer works with ALSA or PulseAudio, without further configuration. But if you use PulseAudio there is simple solution - padsp.
padsp starts the specified program and redirects its access to OSS compatible audio devices (/dev/dsp and auxiliary devices) to a PulseAudio sound server.
Usage is simple - if you want to run let's say yourexec, just add padsp command before this executable: