Also, how can I generate frequencies at the 20kHz range and above?
Mix or add? The two mean different things, or at least they can. To be fair, we call an audio board a "mixing console"...
I'm asking the OP to clarify in which sense he means mixing.Top hit for "sine mixer":en.wikipedia.org/wiki/Frequency_mixerAnd as I said, an audio mixer is generally actually a summing amplifier.Just asking the OP to clear this up.
QuoteAlso, how can I generate frequencies at the 20kHz range and above?That hardly seems audio.
If you are looking for a high resolution i.e. low distortion sin wave, you may want to consider using a direct digital synthesizer (DDS) controlled by the Arduino, then use op amp summer to mix the signal.<a href="http://www.analog.com/library/analogdialogue/archives/38-08/dds.html">Direct Digital Synthesis</a>
We should speak more clearly than the general public does. So with that in mind, what you want to do is -add- several sine waves together, not mix them.