encoder.js

// Copyright 2022 Emilie Gillet.
//
// Author: Emilie Gillet (emilie.o.gillet@gmail.com)
//
// 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.
// 
// See http://creativecommons.org/licenses/MIT/ for more information.
//
// -----------------------------------------------------------------------------
//
// Low-bitrate audio encoder for loading custom data into a module. Designed
// with the following set of constraints in mind:
//
// - Suitable to the low sample rate and bandwidth (a few kHz) of the CV inputs.
// - Modulated signal does not have a DC offset.
// - Robust to deviation in both the emitter and receiver's sample rate.
// - Very low complexity decoder (differentiation + zero-crossing detection).

const CRC = { };

CRC.table = [
  0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f,
  0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
  0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91, 0x1db71064, 0x6ab020f2,
  0xf3b97148, 0x84be41de, 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
  0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
  0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,
  0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b, 0x35b5a8fa, 0x42b2986c,
  0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
  0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423,
  0xcfba9599, 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
  0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190, 0x01db7106,
  0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
  0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d,
  0x91646c97, 0xe6635c01, 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
  0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
  0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
  0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 0x4adfa541, 0x3dd895d7,
  0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,
  0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa,
  0xbe0b1010, 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
  0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81,
  0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,
  0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683, 0xe3630b12, 0x94643b84,
  0x0d6d6a3e, 0x7a6a5aa8, 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
  0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
  0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,
  0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, 0xd6d6a3e8, 0xa1d1937e,
  0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
  0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55,
  0x316e8eef, 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
  0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe, 0xb2bd0b28,
  0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
  0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a, 0x9c0906a9, 0xeb0e363f,
  0x72076785, 0x05005713, 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,
  0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
  0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
  0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 0x8f659eff, 0xf862ae69,
  0x616bffd3, 0x166ccf45, 0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,
  0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc,
  0x40df0b66, 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
  0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, 0xcdd70693,
  0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
  0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d
];

CRC.crc32 = function(crc, data) {
  crc = ~~crc ^ -1;
  for (let n = 0; n < data.length; n++) {
    crc = CRC.table[(crc ^ data[n]) & 0xff] ^ (crc >>> 8);
  }
  return (crc ^ -1);
}

class Encoder {
  constructor(encoding, format) {
    this.sampleRate = encoding.sampleRate;
    this.symbolDurations = encoding.symbolDurations;
    this.packetSize = encoding.packetSize;
    this.samples = [];
    
    const fn = encoding.shape == 'cosine' ? Math.cos : Math.sin;
    const noDC = encoding.shape == 'sine_no_dc';
    for (let duration of encoding.symbolDurations) {
      let gain = noDC ? Math.max(encoding.symbolDurations[0] / duration, 0.5) : 1.0;
      let plus = new Float32Array(duration);
      let minus = new Float32Array(duration);
      for (let i = 0; i < duration; i++) {
        plus[i] = fn(i / duration * Math.PI) * gain;
        minus[i] = -plus[i];
      }
      this.samples.push([plus, minus]);
      this.polarity = 0;
    }
    this.format = format;
  }
  
  encode(symbols) {
    let totalDuration = 0;
    for (let symbol of symbols) {
      totalDuration += this.symbolDurations[symbol];
    }
    let block = new Float32Array(totalDuration);
    let i = 0;
    for (let symbol of symbols) {
      block.set(this.samples[symbol][this.polarity], i);
      i += this.symbolDurations[symbol];
      this.polarity = 1 - this.polarity;
    }
    return block;
  }
  
  codeBlank(duration) {
    let n = Math.ceil(
        duration * this.sampleRate / this.symbolDurations[2]);
    return this.encode(Array(n).fill(2));
  }
  
  pad(data, size) {
    let n = data.length;
    if (n % size != 0) {
      let paddedData = new Uint8Array(n + size - (n % size));
      paddedData.set(data);
      data = paddedData;
    }
    return data;
  }
  
  codePacket(packet) {
    console.assert(packet.length <= this.packetSize);
    packet = this.pad(packet, this.packetSize);
    let crc = CRC.crc32(0, packet);
    let header = new Uint8Array([0x55, 0x55, 0x55, 0x55]);
    let footer = new Uint8Array([
        crc >>> 24,
        (crc >>> 16) & 0xff,
        (crc >>> 8) & 0xff,
        (crc) & 0xff]);
    let symbolStream = [];
    for (let block of [header, packet, footer]) {
      for (let byte of block) {
        for (let bit = 0; bit < 8; bit++) {
          symbolStream.push(byte & (0x80 >> bit) ? 1 : 0);
        }
      }
    }
    return this.encode(symbolStream);
  }
  
  code(data, tags) {
    // Replace the last bytes of data with the tag.
    data = this.pad(data, this.format.pageSize);
    for (let i = 0; i < tags.length; i++) {
      data[data.length - tags.length + i] = tags[i];
    }

    // Collect all pieces of the output signal.
    let buffers = [];
    buffers.push(this.codeBlank(this.format.introDuration));
    for (let i = 0; i < data.length; i += this.packetSize) {
      buffers.push(this.codePacket(data.slice(i, i + this.packetSize)));
      if (i % this.format.pageSize == 0) {
        buffers.push(this.codeBlank(this.format.blankDuration));
      }
    }
    buffers.push(this.codeBlank(this.format.outroDuration));
    
    // Compute the total size.
    let totalSize = 0;
    for (let buffer of buffers) {
      totalSize += buffer.length;
    }
    
    // Splice everything together.
    let output = new Float32Array(totalSize);
    let i = 0;
    for (let buffer of buffers) {
      output.set(buffer, i);
      i += buffer.length;
    }
    return output;
  }
  
  toWAV(audioSamples) {
    let buffer = new ArrayBuffer(44 + audioSamples.length * 2);
    let view = new DataView(buffer);
    
    let writeTag = function(offset, tag) {
      for (let i = 0; i < tag.length; i++) {
        view.setUint8(offset + i, tag.charCodeAt(i));
      }
    }
    
    writeTag(0, 'RIFF');
    view.setUint32(4, 36 + audioSamples.length * 2, true);
    writeTag(8, 'WAVE');
    
    writeTag(12, 'fmt ');
    view.setUint32(16, 16, true);
    view.setUint16(20, 1, true);
    view.setUint16(22, 1, true);
    view.setUint32(24, this.sampleRate, true);
    view.setUint32(28, this.sampleRate * 2, true);
    view.setUint16(32, 2, true);
    view.setUint16(34, 16, true);
    
    writeTag(36, 'data');
    view.setUint32(40, audioSamples.length * 2, true);
    for (let i = 0; i < audioSamples.length; i++) {
      let s = Math.max(-1, Math.min(1, audioSamples[i]));
      view.setInt16(44 + i * 2, s * 32767, true);
    }
    return buffer;
  }
  
  static create() {
    // Default encoding and format for Plaits.
    let encoding = {
      sampleRate: 48000.0,
      symbolDurations: [24, 60, 108],
      packetSize: 256,
      shape: 'cosine'
    };
    let format = {
      pageSize: 256,
      blankDuration: 0.1,
      introDuration: 0.5,
      outroDuration: 1.25
    };
    return new Encoder(encoding, format);
  }
}