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Fb combfilters: generalize/optimize feed-back comb filters #218

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Fb combfilters: generalize/optimize feed-back comb filters #218

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1342a53
Add fi._fb_comb() function, generic feed-back comb filter
oleg-nesterov Feb 23, 2025
9135fcc
Reimplement fi.fb_comb() and fi.fb_fcomb() using fi._fb_comb()
oleg-nesterov Feb 23, 2025
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34 changes: 31 additions & 3 deletions filters.lib
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Original file line number Diff line number Diff line change
Expand Up @@ -247,6 +247,35 @@ declare ff_combfilter copyright "Copyright (C) 2003-2019 by Julius O. Smith III
declare ff_combfilter license "MIT-style STK-4.3 license";
ffcombfilter(maxdel,del,g) = ff_comb(maxdel,del,1,g);

//---------------------`(fi.)_fb_comb`---------------------
// A generic feed-back comb filter
//
// #### Usage
//
// ```
// _ : _fb_comb(dop,N,b0,aN) : _
// ```
//
// Where
//
// * `dop`: delay operator, e.g. `@` or `de.fdelay4a(2048)`
// * `N`: current delay
// * `b0`: gain applied to input
// * `aN`: gain applied to delay-line output
//
// #### Example test program
//
// ```
// process = _fb_comb(@,N,b0,aN);
// ```
// implements the following difference equation:
// ```
// y[n] = b0 x[n] + aN y[n - N]
// ```
//
// See more examples in `filters.lib` below.
// --------------------------------------------------------
_fb_comb(dop,N,b0,aN) = *(aN) + *(b0) ~ dop(N-1);

//-----------------------`(fi.)fb_comb`-----------------------
// Feed-Back Comb Filter (integer delay).
Expand All @@ -272,8 +301,7 @@ ffcombfilter(maxdel,del,g) = ff_comb(maxdel,del,1,g);
declare fb_comb author "Julius O. Smith III";
declare fb_comb copyright "Copyright (C) 2003-2019 by Julius O. Smith III <[email protected]>";
declare fb_comb license "MIT-style STK-4.3 license";
fb_comb(maxdel,N,b0,aN) = (+ <: de.delay(maxdel,N-1),_) ~ *(-aN) : !,*(b0) : mem;

fb_comb(maxdel,N,b0,aN) = _fb_comb(de.delay(maxdel),N,b0,-aN) : mem;

//-----------------------`(fi.)fb_fcomb`-----------------------
// Feed-Back Comb Filter (floating point delay).
Expand All @@ -299,7 +327,7 @@ fb_comb(maxdel,N,b0,aN) = (+ <: de.delay(maxdel,N-1),_) ~ *(-aN) : !,*(b0) : mem
declare fb_fcomb author "Julius O. Smith III";
declare fb_fcomb copyright "Copyright (C) 2003-2019 by Julius O. Smith III <[email protected]>";
declare fb_fcomb license "MIT-style STK-4.3 license";
fb_fcomb(maxdel,N,b0,aN) = (+ <: de.fdelay(maxdel,float(N)-1.0),_) ~ *(-aN) : !,*(b0) : mem;
fb_fcomb(maxdel,N,b0,aN) = _fb_comb(de.fdelay(maxdel),N,b0,-aN) : mem;

//-----------------------`(fi.)rev1`-----------------------
// Special case of `fb_comb` (`rev1(maxdel,N,g)`).
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