Older SB compat cards support the non standard sample rate 6400 Hz.
More modern cards do not support this rate so a standard rate must
be selected in Tools|Dsp Settings.

If you have more than one sound card fitted, recommend that you explicitly set
the sound cards required for input and output in Tools|Dsp settings.  If you use
"Use Auto" the mixer controls (volume and mute) can be mapped to the wrong card.