[DaveC[_2_]]

This is the classic Baxandall tone control.
There is plenty of material if Googling for
'baxandall'.
Tauno Voipio

Thanks! It really helps to know what it's called... ;-)

This page:

http://sound.westhost.com/dwopa2.htm

says:
"
This circuit must be driven from a low impedance, so connecting it after the
volume control (for example) is a no-no. Ideally, the output of an opamp will
be the source, thus ensuring the required low impedance.
"
The input to this circuit will be the output of a computer's sound card. I
don't know if it's an opamp driving the output or not.

What do you suggest to insure driving by low impedance? Add a buffer opamp
(gain of 1) at the input of this circuit?

Thanks.