desc: FFT peak-detecting filter
slider1:5<0,6,1{64,128,256,512,1024,2048,4096}>FFT size
slider2:60<0,24000,10>minimum center freq (Hz)
slider3:8000<0,24000,10>maximum center freq (Hz)
slider4:2<0,8,0.01>filter width (octaves)
slider5:0<-120,24,1>peak gain (dB)
slider6:-120<-120,24,1>nonpeak gain (dB)
slider7:120<0,1000,1>filter position attack time (ms)
slider8:1.29<0.5,1.5,0.01>high end slope

@init 
fftsize=-1;
curfilterpos=-1;

@slider
  fftsize != (0|(2^(slider1+6))) ? (
    fftsize=(2^(slider1+6))|0;
    bpos=0; 
    curblock=0;
    lastblock=65536;
    window=120000;
    hist=240000;
    invfsize=1/fftsize;
    hfftsize=fftsize*0.5;
    tmp=0;
    tsc=3.14159/hfftsize;
    loop(hfftsize,
      window[tmp]=0.42-0.50*cos(tmp*tsc)+0.08*cos(2*tmp*tsc);
      tmp+=1;
    );
  );
  lowband=hfftsize*slider2*2.0/srate;
  lowband = min(max(lowband,0),hfftsize)|0;
  hiband=hfftsize*slider3*2.0/srate;
  hiband = min(max(hiband,0),hfftsize)|0;
  lowband > hiband ? ( t=hiband; hiband=lowband; lowband=t; );
  peakgain = 2 ^ (slider5/6) * invfsize;
  nonpeakgain = 2 ^ (slider6/6) * invfsize;
  attack=  slider7<1 ? 0 : exp(-hfftsize/(slider7*0.001*srate));
  minpeakval=pow(2,-90/6.0);
  hislope=slider8/hfftsize;
  pdc_delay=fftsize;
  pdc_bot_ch=0;
  pdc_top_ch=2;

@sample
bpos >= fftsize ? (

  t=curblock;
  curblock=lastblock;
  lastblock=t;

  fft(curblock,fftsize);
  fft_permute(curblock,fftsize);
  peakpos=curfilterpos;
  peakval=minpeakval;
  i=lowband*2;
  gain=0;
  loop(max(hiband-lowband,1), 
    a=curblock[i];
    b=curblock[i+1];
    cv=(a*a+b*b)*gain*gain;
    gain+=hislope;
    cv > peakval ? ( peakpos=i; peakval=cv; );
    i+=2;
  );

  peakpos *= 0.5;
  curfilterpos = (curfilterpos < 0 ? peakpos : curfilterpos*attack + peakpos*(1-attack));

  curfilterpos >= 0 ? 
  (
    filtersize_l=curfilterpos*slider4*0.25;
    filtersize_r=curfilterpos*slider4*0.5;
  ) 
  : filtersize_l=filtersize_r=0;
//  slider8=curfilterpos; sliderchange(slider8);
 
  ifiltersize_l=1/filtersize_l; 
  ifiltersize_r=1/filtersize_r; 
  i=0;
  pp=0;
  ifilterpos=(curfilterpos+0.5)|0;
  loop(hfftsize, 
    i2=fftsize*2-i-2;
    adjust=nonpeakgain;
    curfilterpos >= 0 ? (
      filtersize_l<=1 ? (
        pp==ifilterpos ? adjust=peakgain;
      ) : (
        dist=pp-curfilterpos;
        dist < 0 ? (
          dist=-dist;
          dist <= filtersize_l ? (
            sc = dist*ifiltersize_l; 
            sc*=sc;
            adjust = peakgain*(1-sc) + nonpeakgain*sc;
          );
        ) : (
          dist <= filtersize_r ? (
            sc = dist*ifiltersize_r;
            sc*=sc;
            adjust = peakgain*(1-sc) + nonpeakgain*sc;
          );
        );
      );

    );
     



    curblock[i]*=adjust; 
    curblock[i+1]*=adjust;
    curblock[i2]*=adjust; 
    curblock[i2+1]*=adjust;
    i+=2; 
    pp+=1;
  );
  fft_ipermute(curblock,fftsize);
  ifft(curblock,fftsize);
  bpos=0;
);

// make sample
w=window[bpos*0.5];
iw=1-w;

os0=spl0;
os1=spl1;

spl0=(curblock[bpos]*w + lastblock[fftsize+bpos]*iw);
spl1=(curblock[bpos+1]*w + lastblock[fftsize+bpos+1]*iw);

lastblock[bpos]=hist[bpos];
lastblock[bpos+1]=hist[bpos+1];
lastblock[fftsize+bpos]=os0;
lastblock[fftsize+bpos+1]=os1;

hist[bpos]=os0;
hist[bpos+1]=os1;
bpos+=2;
