[sdiy] Equal power law

[Neil Johnson]

Hi Rutger,

> Inspired by the lin/exp/log thread, I've been wondering about implementation of other curves, most specifically those used for equal power law and BBC panning law (center at -3dB or center at -4.5dB).
>
> Are there simple ways to approximate these curves in analog domain (e.g. without using a VCA). I've been playing in Spice with an approximation of the curve using a simple opamp circuit with back-to-back zeners. The zeners already have a rather 'soft knee', but I'd like to know if there are ways to get the shape even closer to what's needed for an equal power law curve.

There's a THAT app note where they use diode function generators to
approximate the sin/cos curves for panning VCAs.
Don't remember the number at the moment but there aren't that many
THAT app notes.

Neil
--
http://www.njohnson.co.uk