added per-channel low-pass filter
sounds better, but still clicks and pops a lot. i'll need a volume envelope lowpass filter, i guess.
This commit is contained in:
Andy Sloane
parent
15a848d797
commit
7de75f6977
2 changed files with 74 additions and 23 deletions
75
xm.js
75
xm.js
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@ -22,7 +22,7 @@ function prettify_effect(t, p) {
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function prettify_notedata(note, inst, vol, efftype, effparam) {
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return (prettify_note(note) + " " + prettify_number(inst) + " "
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+ prettify_number(vol) + " "
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+ prettify_number(vol) + " "
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+ prettify_effect(efftype, effparam));
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}
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@ -56,6 +56,28 @@ function GetEnvelope(env, ticks) {
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return y0;
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}
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// Return 2-pole Butterworth lowpass filter coefficients for
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// center frequncy f_c (relative to sampling frequency)
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function FilterCoeffs(f_c) {
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// if (f_c > 0.5) { // we can't lowpass above the nyquist frequency...
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// return [1, 0, 0];
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// }
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var wct = Math.sqrt(2) * Math.PI * f_c;
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var e = Math.exp(-wct);
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var c = e * Math.cos(wct);
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var s = e * Math.sin(wct);
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var gain = (1 - 2*c + c*c + s*s) / 2;
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return [gain, 2*c, -c*c - s*s];
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}
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function Filter(x, coef, state) {
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var y = coef[0] * (x + state[0]) + coef[1]*state[1] + coef[2]*state[2];
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state[0] = x;
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state[2] = state[1];
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state[1] = y;
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return y;
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}
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var cur_songpos = -1, cur_pat = -1, cur_row = 64, cur_ticksamp = 0;
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var cur_tick = 6;
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function next_row(f_smp) {
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@ -107,6 +129,7 @@ function next_row(f_smp) {
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channelinfo[i].off = 0;
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channelinfo[i].release = 0;
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channelinfo[i].envtick = 0;
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channelinfo[i].filter = FilterCoeffs(channelinfo[i].doff / 2);
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// console.log("channel", i, r[i][0], channelinfo[i]);
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// if there's an instrument and a note, set the volume
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if (r[i][0] != -1) {
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@ -140,21 +163,22 @@ function next_tick(f_smp) {
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next_row(f_smp);
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}
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for (var j = 0; j < nchan; j++) {
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var inst = channelinfo[j].inst;
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var ch = channelinfo[j];
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var inst = ch.inst;
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if (inst === undefined) continue;
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if (inst.env_vol !== undefined) {
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channelinfo[j].env_vol = GetEnvelope(inst.env_vol, channelinfo[j].envtick);
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ch.env_vol = GetEnvelope(inst.env_vol, ch.envtick);
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if (inst.env_vol_type & 2) { // sustain loop?
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// if we're sustaining a note, leave env_vol alone
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if (channelinfo[j].release == 0) {
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if (channelinfo[j].envtick >= inst.env_vol[inst.env_vol_sustain*2]) {
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if (ch.release == 0) {
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if (ch.envtick >= inst.env_vol[inst.env_vol_sustain*2]) {
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continue;
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}
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}
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}
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channelinfo[j].envtick++;
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ch.envtick++;
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} else {
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channelinfo[j].env_vol = 64;
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ch.env_vol = 64;
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}
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}
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}
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@ -168,7 +192,7 @@ function audio_cb(e) {
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dataR.fill(0);
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var offset = 0;
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var ticklen = 0|(f_smp * 2.5 / bpm);
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while(buflen > 0) {
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if (cur_ticksamp >= ticklen) {
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next_tick(f_smp);
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@ -176,52 +200,55 @@ function audio_cb(e) {
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}
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var tickduration = Math.min(buflen, ticklen - cur_ticksamp);
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for (var j = 0; j < nchan; j++) {
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var inst = channelinfo[j].inst;
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var ch = channelinfo[j];
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var inst = ch.inst;
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if (inst === undefined) continue;
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var samp = inst.sampledata;
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var sample_end = inst.len;
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var looplen = 0;
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var loop = false;
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if (inst.type & 3) {
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if ((inst.type & 3) == 1) { // todo: support pingpong
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loop = true;
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looplen = inst.looplen;
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sample_end = looplen + inst.loop;
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}
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var samplen = inst.len;
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var env_vol = channelinfo[j].env_vol / 64.0;
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var volL = env_vol * channelinfo[j].volL / 64.0;
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var volR = env_vol * channelinfo[j].volR / 64.0;
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var env_vol = ch.env_vol / 64.0;
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var volL = env_vol * ch.volL / 64.0;
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var volR = env_vol * ch.volR / 64.0;
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if (volL < 0) volL = 0;
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if (volR < 0) volR = 0;
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if (volR == 0 && volL == 0)
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continue;
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var k = channelinfo[j].off;
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var dk = channelinfo[j].doff;
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// console.log(j, offset, channelinfo[j]);
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var k = ch.off;
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var dk = ch.doff;
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// console.log(j, offset, ch);
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for (var i = offset; i < offset+tickduration; i++) {
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var kk = k|0;
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var si = samp[kk];
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/*
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// bilinear filtering
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var sj = si;
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if (kk < sample_end-1)
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sj = samp[kk+1];
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var t = k - kk;
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si = t * sj + (1 - t) * si;
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dataL[i] += volL * si;
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dataR[i] += volR * si;
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*/
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dataL[i] += Filter(volL * si, ch.filter, ch.filterstate[0]);
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dataR[i] += Filter(volR * si, ch.filter, ch.filterstate[1]);
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k += dk;
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if (k >= sample_end) { // TODO: implement pingpong looping
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if (loop) {
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k -= looplen;
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} else {
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// kill sample
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channelinfo[j].inst = undefined;
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ch.inst = undefined;
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break;
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}
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}
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}
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channelinfo[j].off = k;
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channelinfo[j].doff = dk;
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ch.off = k;
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ch.doff = dk;
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}
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offset += tickduration;
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cur_ticksamp += tickduration;
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@ -269,7 +296,9 @@ function playXM(arrayBuf) {
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tempo = dv.getUint16(0x4c, true);
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bpm = dv.getUint16(0x4e, true);
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for (var i = 0; i < nchan; i++) {
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channelinfo.push({})
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channelinfo.push({
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filterstate: [new Float32Array(3), new Float32Array(3)]
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})
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}
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console.log("header len " + hlen);
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@ -332,7 +361,7 @@ function playXM(arrayBuf) {
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}
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patterns.push(pattern);
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}
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// now load instruments
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for (i = 0; i < ninst; i++) {
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var hdrsiz = dv.getUint32(idx, true);
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