linear remapping is not so hard if you can define your remapping mathematically. i'm a bit of a fan of this function (which i'll write as an expr for handy use).
[expr~ 2/(1+pow($f2,-$f1))-1]
your input goes in the left, the signal on the right is a control (sensible values >1).
in theory this maps input values between +/- infinity into +/- 1. but because of the limited precision of floating point math, they eventually just end up being exactly equal to +/- 1 at some range. for a control of 2 this is about +/- 80. for 1.01 this is about +/- 1500.
this function is normally called the sigmoid function and is used in neural networks.. the control is normally 'e', which probably gives the resulting curve a perfect quality that my primitive mathematical understanding can not appreciate.
also, foldover distortion is the effect you get when frequencies higher than 0.5*samplerate (nyquist frequency) are produced. so-called because they are 'folded' back in frequency space, so a frequency at nyquist+100hz creates a kind of ghost frequency lurking around nyquist-100hz.
the kind of distortion you are referring to is the kind of god-awful clipping that old soundblaster cards (and surely other hardware) did. where values where wrapped around the +/- boundaries instead of clipping. you can recreate it (why!?) using wrap~ (after some massaging of the signal) like this,
[+~ 1] | [/~ 2] //get the unclipped signal into [0,1] | [wrap~] | [*~ 2] | [-~ 1] //shift it back to [-1,1]
(you could do the massaging using scale, but i'm never sure what library it's in)
... if anyone knows of a good description of all of the different distortions that come into play when an FM or AM radio signal is poorly recieved, please fill me in.
pix.
On Mon, Jul 19, 2004 at 09:22:34AM -0700, Lex Ein wrote:
Add linear remapping, where the instantaneous signal is used as an index to a table. Easy for 8,12, and 16-bit audio. Not so easy for 20-bit or 24-bit, heh. This can be used to create compression, expansion, clipping, dynamics inversion, etc. L ba wrote:
what kinds of distortion are there other than clipping and foldover? I figure fold over is where the signal is flipped back instead of clipping.
what are some other common waveshaping effects?
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