I've gone through the archives here and found a lot of good posts, but I still have questions.

I was looking at Chamberlain's Musical Applications of Microprocessors tonight and was studying his section on filters. There's a diagram of a digital integrator - it simply takes the previous output, adds it to the input, and stores the results. There's a couple of graphs showing the results of running sine waves through it.

Can a digital integrator be thought of as a filter?

Next Chamberlain describes the RC circuit. I'm familiar with this in that I've used it to create my ADSR envelope. From the diagram in Chamberain, the digital version looks like a digital integrator with the input run through an amplifier. The delayed output is also run through an amplifier before being summed with the amplified input. In digital terms, the amplifiers simply multiply their inputs. Programmically, it looks like this:

Code: Select all

```
output = a0 * input + b1 * output;
```

Is it possible to add resonance to the above filter? If so, where?

I was looking at the diagram for the state variable filter, and it looks like two cascaded digital integrators with an amplifier placed between them and one placed before the first one. There are also other elements on the diagram as well. As I understand it the state variable filter is a two pole filter.

I see where the resonance is coming from; it's the output of the first digital integrator fed through an amplifier and subtracted from the input.

Anyway, it could be that I'm still in over my head with this stuff and need to do a lot more homework, but I think I'm making progress. My goal is to reach a point where I may not have a complete command over the theory but know at least enough to play with a 2 pole filter with resonance and have a halfway decent idea of what I'm doing.

Thanks for any help.