desc:Upsamp Test

@init

upsampfact=8;

filtlen = 25;
datasize=100;
filtb=0; // size filtlen
input=filtb+filtlen; // size datasize
output=input+datasize; // size datasize*upsampfact
work=output+datasize*upsampfact; // size datasize*upsampfact

// create the original waveform in the input buffer:
didx=0;
loop(datasize,
  input[didx]=sin(2*2*$pi*didx/datasize)+sin(20.3834724*2*$pi*didx/datasize);
  didx+=1;
);

// srate 44100 upsampled 8X 25-order 0.5442176870748299-Hz, 0.1360544217687075-Hz-width linear phase FIR lowpass
// e.g. at 44.1k that's a 12kHz cutoff with 3kHz transition
filtb[0] = 0.0125287023096614606038068373550231626722961664199829101562500000000000000000000000000000000000000000;
filtb[1] = 0.0178100495406813379151156340185480075888335704803466796875000000000000000000000000000000000000000000;
filtb[2] = 0.0232562730997107544594904027235315879806876182556152343750000000000000000000000000000000000000000000;
filtb[3] = 0.0287370345711178490355486303542420500889420509338378906250000000000000000000000000000000000000000000;
filtb[4] = 0.0341170092244123396296728856214031111449003219604492187500000000000000000000000000000000000000000000;
filtb[5] = 0.0392600347372514466015580580915411701425909996032714843750000000000000000000000000000000000000000000;
filtb[6] = 0.0440333482528297986968723876088915858417749404907226562500000000000000000000000000000000000000000000;
filtb[7] = 0.0483117659859851472647918058100913185626268386840820312500000000000000000000000000000000000000000000;
filtb[8] = 0.0519816604677718271942943317753815790638327598571777343750000000000000000000000000000000000000000000;
filtb[9] = 0.0549445967117400263513005143067857716232538223266601562500000000000000000000000000000000000000000000;
filtb[10] = 0.0571204998906782099310497358146676560863852500915527343750000000000000000000000000000000000000000000;
filtb[11] = 0.0584502431287390947223236992158490465953946113586425781250000000000000000000000000000000000000000000;
filtb[12] = 0.0588975641588412590632373166954494081437587738037109375000000000000000000000000000000000000000000000;
filtb[13] = 0.0584502431287390947223236992158490465953946113586425781250000000000000000000000000000000000000000000;
filtb[14] = 0.0571204998906782099310497358146676560863852500915527343750000000000000000000000000000000000000000000;
filtb[15] = 0.0549445967117400263513005143067857716232538223266601562500000000000000000000000000000000000000000000;
filtb[16] = 0.0519816604677718271942943317753815790638327598571777343750000000000000000000000000000000000000000000;
filtb[17] = 0.0483117659859851472647918058100913185626268386840820312500000000000000000000000000000000000000000000;
filtb[18] = 0.0440333482528297986968723876088915858417749404907226562500000000000000000000000000000000000000000000;
filtb[19] = 0.0392600347372514466015580580915411701425909996032714843750000000000000000000000000000000000000000000;
filtb[20] = 0.0341170092244123396296728856214031111449003219604492187500000000000000000000000000000000000000000000;
filtb[21] = 0.0287370345711178490355486303542420500889420509338378906250000000000000000000000000000000000000000000;
filtb[22] = 0.0232562730997107544594904027235315879806876182556152343750000000000000000000000000000000000000000000;
filtb[23] = 0.0178100495406813379151156340185480075888335704803466796875000000000000000000000000000000000000000000;
filtb[24] = 0.0125287023096614606038068373550231626722961664199829101562500000000000000000000000000000000000000000;

// uses only filtb
function applyFIRFilter(srcbuf, destbuf, buflen)
(
  memset(destbuf,0,filtlen); // assume zeros in output for beginning

  afidx=filtlen-1;
  loop(buflen-filtlen+1,
  
    newy=srcbuf[afidx]*filtb[0];

    fidx=1;
    loop(filtlen-1,
      newy += srcbuf[afidx-fidx]*filtb[fidx];
      fidx+=1;
    );

    destbuf[afidx]=newy;
    afidx+=1;
  );
);

function upsampleBuffer(srcbuf, uslen, usfact, workbuf, destbuf)
(
  // zero-stuff
  usidx=0;
  loop(uslen,
    workbuf[usidx*usfact]=srcbuf[usidx];
    memset(workbuf+usidx*usfact+1,0,usfact-1);
    usidx+=1;
  );
  
  // low-pass filter
  applyFIRFilter(workbuf, destbuf, uslen*usfact);
);

upsampleBuffer(input, datasize, upsampfact, work, output);

draw=1;

@gfx

// both graphs are normalized for vertical scale, so if one has a peak or lacks a peak, it might scale unexpectedly

gfx_w != lastx || gfx_y != lasty ? draw=1;
lastx=gfx_w; lasty=gfx_y;

draw ?
(
  dmin=9999999999999999999;
  dmax=-dmin;
  gdidx=0;
  loop(datasize,
    dmin=min(dmin, input[gdidx]);
    dmax=max(dmax, input[gdidx]);
    gdidx+=1;
  );

  gfx_set(.5,.5,1,.8);
  gfx_x=0;
  gfx_y=gfx_h/2;
  gdidx=-1;
  loop(datasize, gfx_lineto(gfx_w*(gdidx+=1)/(datasize-1), gfx_h/2-(gfx_h/2)*(2*(input[gdidx]-dmin)/(dmax-dmin)-1)));

  dmin=9999999999999999999;
  dmax=-dmin;
  gdidx=0;
  loop(datasize*upsampfact,
    dmin=min(dmin, output[gdidx]);
    dmax=max(dmax, output[gdidx]);
    gdidx+=1;
  );

  gfx_set(1,.5,.5,.8);
  gfx_x=0;
  gfx_y=gfx_h/2;
  gdidx=0;
  loop(datasize*upsampfact,
    gfx_lineto(gfx_w*(gdidx-(filtlen-1)/2)/(datasize*upsampfact-upsampfact),
               gfx_h/2-(gfx_h/2)*(2*(output[gdidx]-dmin)/(dmax-dmin)-1));
    gdidx+=1;
  );

  gfx_x=5;gfx_y=gfx_h-20;
  gfx_set(1,1,1,1);
  gfx_drawstr("Original in blue, upsampled in pink.");
  draw=0;
)