Audio frequency modulator

I'm developing an audio annunciator that needs to modulate a sinewave of three different freq's.

Simply turning the sinewave on and off results in an aural "popping" artifact that is objectional.

I suspect that I need to "mix" the desired tone with a much slower sine wave that will provide the desired "turn on and turn off effect", but with a variable slope that will either remove or reduce this "popping" artifact.

Ideally my circuit needs to be controllable via SPI or I2C buss with a microcontroller.

I'm aware of function generator chips such as the XR2206 and MAX038, etc., but they require too much calibration and manual control for my application.

Can anyone on the forum direct me to a source of data for such a device/circuit.

You're not terrribly clear on what you want?, but I suggest you try searching for 'envelope shaper' and 'VCA' (voltage controlled amplifier).

I suspect you're looking for a vocoder type effect?, and you might try searching for that as well?.

Do a search on "digital audio pot" and "digital audio gain control".