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added per-channel low-pass filter

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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 2015-10-23 17:34:52 -07:00
commit 7de75f6977
2 changed files with 74 additions and 23 deletions
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22
LICENSE Normal file
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@ -0,0 +1,22 @@
The MIT License (MIT)
Copyright (c) 2015 Andy Sloane <andy@a1k0n.net>
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.

69
xm.js
View file

@ -56,6 +56,28 @@ function GetEnvelope(env, ticks) {
return y0;
}
// Return 2-pole Butterworth lowpass filter coefficients for
// center frequncy f_c (relative to sampling frequency)
function FilterCoeffs(f_c) {
// if (f_c > 0.5) { // we can't lowpass above the nyquist frequency...
// return [1, 0, 0];
// }
var wct = Math.sqrt(2) * Math.PI * f_c;
var e = Math.exp(-wct);
var c = e * Math.cos(wct);
var s = e * Math.sin(wct);
var gain = (1 - 2*c + c*c + s*s) / 2;
return [gain, 2*c, -c*c - s*s];
}
function Filter(x, coef, state) {
var y = coef[0] * (x + state[0]) + coef[1]*state[1] + coef[2]*state[2];
state[0] = x;
state[2] = state[1];
state[1] = y;
return y;
}
var cur_songpos = -1, cur_pat = -1, cur_row = 64, cur_ticksamp = 0;
var cur_tick = 6;
function next_row(f_smp) {
@ -107,6 +129,7 @@ function next_row(f_smp) {
channelinfo[i].off = 0;
channelinfo[i].release = 0;
channelinfo[i].envtick = 0;
channelinfo[i].filter = FilterCoeffs(channelinfo[i].doff / 2);
// console.log("channel", i, r[i][0], channelinfo[i]);
// if there's an instrument and a note, set the volume
if (r[i][0] != -1) {
@ -140,21 +163,22 @@ function next_tick(f_smp) {
next_row(f_smp);
}
for (var j = 0; j < nchan; j++) {
var inst = channelinfo[j].inst;
var ch = channelinfo[j];
var inst = ch.inst;
if (inst === undefined) continue;
if (inst.env_vol !== undefined) {
channelinfo[j].env_vol = GetEnvelope(inst.env_vol, channelinfo[j].envtick);
ch.env_vol = GetEnvelope(inst.env_vol, ch.envtick);
if (inst.env_vol_type & 2) { // sustain loop?
// if we're sustaining a note, leave env_vol alone
if (channelinfo[j].release == 0) {
if (channelinfo[j].envtick >= inst.env_vol[inst.env_vol_sustain*2]) {
if (ch.release == 0) {
if (ch.envtick >= inst.env_vol[inst.env_vol_sustain*2]) {
continue;
}
}
}
channelinfo[j].envtick++;
ch.envtick++;
} else {
channelinfo[j].env_vol = 64;
ch.env_vol = 64;
}
}
}
@ -176,52 +200,55 @@ function audio_cb(e) {
}
var tickduration = Math.min(buflen, ticklen - cur_ticksamp);
for (var j = 0; j < nchan; j++) {
var inst = channelinfo[j].inst;
var ch = channelinfo[j];
var inst = ch.inst;
if (inst === undefined) continue;
var samp = inst.sampledata;
var sample_end = inst.len;
var looplen = 0;
var loop = false;
if (inst.type & 3) {
if ((inst.type & 3) == 1) { // todo: support pingpong
loop = true;
looplen = inst.looplen;
sample_end = looplen + inst.loop;
}
var samplen = inst.len;
var env_vol = channelinfo[j].env_vol / 64.0;
var volL = env_vol * channelinfo[j].volL / 64.0;
var volR = env_vol * channelinfo[j].volR / 64.0;
var env_vol = ch.env_vol / 64.0;
var volL = env_vol * ch.volL / 64.0;
var volR = env_vol * ch.volR / 64.0;
if (volL < 0) volL = 0;
if (volR < 0) volR = 0;
if (volR == 0 && volL == 0)
continue;
var k = channelinfo[j].off;
var dk = channelinfo[j].doff;
// console.log(j, offset, channelinfo[j]);
var k = ch.off;
var dk = ch.doff;
// console.log(j, offset, ch);
for (var i = offset; i < offset+tickduration; i++) {
var kk = k|0;
var si = samp[kk];
/*
// bilinear filtering
var sj = si;
if (kk < sample_end-1)
sj = samp[kk+1];
var t = k - kk;
si = t * sj + (1 - t) * si;
dataL[i] += volL * si;
dataR[i] += volR * si;
*/
dataL[i] += Filter(volL * si, ch.filter, ch.filterstate[0]);
dataR[i] += Filter(volR * si, ch.filter, ch.filterstate[1]);
k += dk;
if (k >= sample_end) { // TODO: implement pingpong looping
if (loop) {
k -= looplen;
} else {
// kill sample
channelinfo[j].inst = undefined;
ch.inst = undefined;
break;
}
}
}
channelinfo[j].off = k;
channelinfo[j].doff = dk;
ch.off = k;
ch.doff = dk;
}
offset += tickduration;
cur_ticksamp += tickduration;
@ -269,7 +296,9 @@ function playXM(arrayBuf) {
tempo = dv.getUint16(0x4c, true);
bpm = dv.getUint16(0x4e, true);
for (var i = 0; i < nchan; i++) {
channelinfo.push({})
channelinfo.push({
filterstate: [new Float32Array(3), new Float32Array(3)]
})
}
console.log("header len " + hlen);