What's the math for mapping Filter 3 cutoff values to track effect

Renoise Tool Development Renoise XML Fileformats & Tools
1

Hello,

What’s the math behind mapping Filter 3 cutoff range (0-22050Hz) to effect column values between 0-255? It’s nonlinear and my skills are too poor to reverse-engineer it ;_;

Thanks!

2

According to Excel, it’s extremely close to:
kHz = (POWER(10,X/127)-1)*0.2205

Where X is 0-255.

Probably more clearly expressed as Hz = (10^(X/127)-1)*22050 / 100

3

Yips:

kCutoffScaling = 100.0

CutoffLinToLog(Value) (::pow(10.0, ::log10(kCutoffScaling) * Value) / (kCutoffScaling - 1.0) - 1.0 / (kCutoffScaling - 1.0))

with Value [0.0 - 1.0], result is Hz / 22050.0

4

Thanks!

How does one use Excel/Gnumeric/OpenOffice to calculate such equations, btw?

And OT: are there any plans to add Python bindings to Renoise (Python being de-facto scripting/extension language in most creative programs as it’s easy enough for artists)?