Arduino wavetable synthesis: Implementing an envelope.

[mubase]

Hi everyone.
I am going a bit nuts trying to implement a simple decay to a wavetable synth I am working on using an ATXmega board and the Arduino IDE.
I can output a sine wavetable through the DAC quite easily. I use a calculated wavetable in an array of 256 values with a maximum value of 4095 as the DAC is 12 bits.
I can then use an accumulator and phase incrementer to get a wide frequency scale.
The output from the dac is done inside a timer overflow IRQ with a sample rate of around 31250Hz.
I would like to know how to implement an envelope. A simple decaying envelope to start with. So, say, I press a button and on button press detect, start the sound and decay. I want to do it using another wavetable containing a simple ramp wave to start with. Can some one explain to me how I would go about this?

The basic snippet of code that is playing the wave looks like this:

[elmegil]

Multiplication

Seriously; you'll need to scale the result appropriately, but that's really what is going on.

PS: Make sure you use integer math as much as possible; probably would want to pre-scale your wavetables.

[mubase]

Hi Elmegil.

Yep. Thanks. My problem was scaling.
All working well now.
Also, I've migrated from xmega to stm32f4 on Arduino IDE. So much faster and nicer.
I'm now doing experiments with rudimentary (and i say RUDIMENTARY) synchronous granular synthesis.