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nlfilt

    ar   nlfilt    ain, ka, kb, kd, kL, kC

DESCRIPTION

Implements the filter Y{n} =a Y{n-1} + b Y{n-2} + d Y^2{n-L} + X{n} - C described in Dobson and Fitch (ICMC'96)

EXAMPLE:

i) Non-linear effect:
        a = b = 0 
        d = 0.8, 0.9, 0.7
        C = 0.4, 0.5, 0.6
        L = 20
This affects the lower register most but there are audible effects over the whole range. We suggest that it may be useful for colouring drums, and for adding arbitrary highlights to notes

ii) Low Pass with non-linear:

        a = 0.4
        b = 0.2
        d = 0.7 
        C = 0.11
        L = 20, ... 200
There are instability problems with this variant but the effect is more pronounced of the lower register, but is otherwise much like the pure comb. Short values of L can add attack to a sound.

iii) High Pass with non-linear: The range of parameters are

        a = 0.35
        b = -0.3
        d = 0.95
        C = 0,2, ... 0.4
        L = 200
iv) High Pass with non-linear: The range of parameters are
        a = 0.7 
        b = -0.2, ... 0.5
        d = 0.9 
        C = 0.12, ... 0.24
        L = 500, 10
The high pass version is less likely to oscillate. It adds scintillation to medium-high registers. With a large delay L it is a little like a reverberation, while with small values there appear to be formant-like regions. There are arbitrary colour changes and resonances as the pitch changes. Works well with individual notes.

Warning: The "useful" ranges of parameters are not yet mapped.
 

AUTHOR:

John ffitch
University of Bath/Codemist Ltd
Bath, UK
1997
 


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