It’s high time to post something new here! This time it’s not for the faint-hearted but goes more into the nitty-gritty of filters. The topic is the state-variable filter. I first heard of that when I went to university in the 1970’s: Helmuth Lemme (now GITEC honorary member and author of a whole number of books – see also the last posting here) had explained this type of filter (then of course in analog form) in his early publications. Since he mentioned the filter as an ingredient to the then completely legendary and (in Germany at the time) utterly elusive Alembic basses and guitars, it had to be something special and very useful. Indeed it proved to be just that when I put a corresponding circuit together back in the day for my first home studio.

Fast forward to now: GITEC friend and member Helmut Keller has picked up the topic and elaborates on it further – specifically for applications in the by now ubiquitous digital domain. He stresses how this filter design is also highly suitable for varying filter-parameters i.e. get some dynamics into the sonic landscape.

Check out Helmut’s article here:

Digital State-Variable Filters.pdf

For those „in the know“ of (digital) signal processing, this article by Helmut K. should be rather enriching – have fun with it. To those readers who will be looking with wonder at the mathematics: do come back – there will be again „lighter reading“ here in the future …. 

Best regards,

Tilmann