riff-wave-pcm.js

/**
 * RIFF WAVE PCM file generator
 * Reference: www-mmsp.ece.mcgill.ca/Documents/AudioFormats/WAVE/WAVE.html
 *
 * @author Lara Sophie Schütt (@literallylara)
 * @license CC0
 */

const DUR = 5     // duration in seconds
const NCH = 1     // number of channels
const SPS = 44100 // samples per second
const BPS = 1     // bytes per sample

const SIZE = DUR * NCH * SPS * BPS

// PCM Data
// --------------------------------------------
// Field           | Bytes | Content
// --------------------------------------------
// ckID            |     4 | "fmt "
// cksize          |     4 | 0x0000010 (16)
// wFormatTag      |     2 | 0x0001 (PCM)
// nChannels       |     2 | NCH
// nSamplesPerSec  |     4 | SPS
// nAvgBytesPerSec |     4 | NCH * BPS * SPS
// nBlockAlign     |     2 | NCH * BPS * NCH
// wBitsPerSample  |     2 | BPS * 8

// data_size = DUR * NCH * SPS * BPS
// file_size = 44 (Header) + data_size

function dec2hex(n, l)
{
    n = n.toString(16)
    return new Array(l*2-n.length+1).join("0") + n
}

function hex2str(hex)
{
    let str = []

    if (hex.length % 2)
    {
        throw new Error("hex2str(\"" + hex + "\"): invalid input (# of digits must be divisible by 2)")
    }

    for (let i = 0; i < hex.length; i+=2)
    {
        str.push(String.fromCharCode(parseInt(hex.substr(i,2),16)))
    }

    return str.reverse().join("")
}

function put(n, l)
{
    return hex2str(dec2hex(n,l))
}

let data = "RIFF" + put(44 + SIZE, 4) + "WAVEfmt " + put(16, 4)

data += put(1              , 2) // wFormatTag (pcm)
data += put(NCH            , 2) // nChannels
data += put(SPS            , 4) // nSamplesPerSec
data += put(NCH * BPS * SPS, 4) // nAvgBytesPerSec
data += put(NCH * BPS      , 2) // nBlockAlign
data += put(BPS * 8        , 2) // wBitsPerSample

data += "data" + put(SIZE, 4)

for (let i = 0; i < DUR; i++)
{        
    for (let j = 0; j < SPS; j++)
    {
        data += put(Math.floor((Math.sin(j/SPS * Math.PI * 2 * 440) + 1) / 2 * Math.pow(2, BPS * 8)), BPS)
    }
}

const WAV = new Audio("data:Audio/WAV;base64," + btoa(data))

WAV.setAttribute("controls","controls");
WAV.play();

document.body.appendChild(WAV)

/* Minified version with pre-defined header

    // RIFF WAVE PCM | Mono | 44100Hz | 8 bit
    for(i=44100*DUR,d="";i--;)d+=String.fromCharCode(~~((Math.sin(i/44100*6.283*440)+1)*128))
    new Audio("data:Audio/WAV;base64,"+btoa("RIFFdataWAVEfmt "+atob("EAAAAAEAAQBErAAARKwAAAEACABkYXRh/////w==")+d)).play()

    // Web Audio API equivalent (assumes 44100 kHz sample rate)
    a=new AudioContext()
    s=a.createScriptProcessor(t=b=4096,1,1)
    s.connect(a.destination)
    s.onaudioprocess=function(e){for(i=0;i<b;)e.outputBuffer.getChannelData(0)[i++]=Math.sin(t++/44100*6.283*440)}

*/

Line 65 returns 256 if I put an odd number as a frequency, which ends up translating to x100 (xFF +1). Probably beacuse if sin retruns 1, it's multuplied by 256 instead of 255.

I replaced:
data += put(Math.floor((Math.sin(j/SPS * Math.PI * 2 * 440) + 1) / 2 * Math.pow(2, BPS * 8)), BPS);

with

data += put(Math.round((Math.sin(j/SPS * Math.PI * 2 * 440) + 1) / 2 * (Math.pow(2, BPS * 8)-1) ), BPS);

how do you combine multiple audio files into a single wav file?

@aahedi You can read each file and merge the channels.