If you're recording acoustically via microphones, then the characteristics of your room, the choice of microphone and the placement of the microphones relative to the room and the instrument will have a *dramatic* affect on the sound you end up with. If you're recording the guitar/viola via DI, then your magnetic/piezo pickups will have a huge effect also.

It's difficult to give any helpful advice unless you can explain what you're doing at the moment, the sound that results, and how that differs from what you want to be achieving :)

I completely agree with the last post. Microphone technique is 98% of the battle with acoustic instruments. I did find this Frequency Chart online and it may help with EQ settings. It is interactive so just move your mouse about and it gives you basic information about instruments frequency range and general EQ settings. A good basic guide.

http://www.independentrecording.net/irn/resources/freqchart/main_display.htm

hey, that's a nice chart. Would be great to implement in Max and have sounds to go with it!

On the original question, look to filtergraph~ and biquad~, maybe cascade the biquad~ to make an EQ, but be sparing with your settings as things will start to sound unnatural pretty quickly...

as stated, having the absolute best and cleanest sound to begin with is paramount!

Thanks for the posts! I like the chart... and I'll look in filtergraph~ and biquad~