/dev/dsp not found

When starting Asterisk I’m seeing the following entries in the log files:

The soundcard device is installed:

Oct 7 19:45:09 ipabx kernel: intel8x0_measure_ac97_clock: measured 49778 usecs Oct 7 19:45:09 ipabx kernel: intel8x0: clocking to 48000
…with 660 permissions on /dev/dsp assigned to root:audio. I have also added the asterisk user to the audio group. Alsa has been started and all looks well. But not only do I get these messages, I’m finding there’s also some cracking sounds when using the GSM codec, and the music-on-hold sounds badly distorted.

Interestingly enough, I tried to set /dev/dsp to o+rw but the situation remains the same.

Are these two issues connected and where should I look to resolve this?