kc85-player.js

/*
 * Robotron KC85 player using the web audio API (https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_API)
 * Origin: https://github.com/chhu/kc85-tape-player
 */


const KC85Config = {
	default : {
		zero     : 2000,  // Frequencies
		zero_amp : 1,
		one      : 1100,
		one_amp  : 1,
		stop     : 550,
		stop_amp : 1,
		first    : 8000,  // N complete "one" waves for first block
		silence  : 4400,  // silence between blocks in samples (0.1s if sampling rate is 48k)
		block    : 160,   // N complete "one" waves for each block
	},

	turbo: {	// just need to specify overrides
		silence : 0,
		block: 0
	}
}

class KC85Player {
	constructor(raw_data, config_key) {    // RAW data should be ByteArray or normal array, config key optional
		this.raw_data = raw_data
		this.config = Object.assign({}, KC85Config.default);
		this.config = Object.assign(this.config, KC85Config[config_key]);
		this.ac = new (window.AudioContext || window.webkitAudioContext)()
		this.sample_rate = this.ac.sampleRate
		this.audio = this.ac.createBuffer(1, this.sample_rate * ((raw_data.length / 128) * 1.2 + 10), this.sample_rate)
		this.duration = this.audio.duration
		this.one = KC85Player.WaveGen(this.sample_rate, this.config.one, this.config.one_amp)
		this.zero = KC85Player.WaveGen(this.sample_rate, this.config.zero, this.config.zero_amp)
		this.stop = KC85Player.WaveGen(this.sample_rate, this.config.stop, this.config.stop_amp)

		// Generate audio samples
		this.audio_pos = 0  // within audio
		this.data_pos = 0  // within raw_data
		this.block = 1

		// Prepare first block
		for (let i = 0; i < this.config.first; i++) 
			this.add_one()

		while (this.data_pos < raw_data.length) {
			// Prepare complete block
			for (let i = 0; i < this.config.block; i++) 
				this.add_one()
			this.add_stop()
			let sum = 0
			this.add_byte((raw_data.length - this.data_pos) <= 128 ? 0xFF : this.block)
			for (let i = 0; i < 128; i++) {
				let data = Number(raw_data[this.data_pos]) // we may read beyond end, should yield zero
				if (isNaN(data))
					data = 0
				sum += data
				this.add_byte(data)
				this.data_pos++
			}
			this.add_byte(sum)
			this.audio_pos += this.config.silence
			this.block++
			if (this.block >= 0xFF)
				this.block = 1
		}
		let signal = this.audio.getChannelData(0).slice(0, this.audio_pos)
		this.audio = this.ac.createBuffer(1, this.audio_pos, this.sample_rate)
		this.audio.copyToChannel(signal, 0, 0)
	}

	static WaveGen(sample_rate, frequency, amplitude) {  // Generates a single wave for given frequency and sr
		let result = new Float32Array(Math.round(sample_rate / frequency))
		let h = result.length / 2; // half
		result[0] = result[h] = 0;
		result[1] = result[h-1] = amplitude * 0.5;
		result[2] = result[h-2] = amplitude * 1;
		result[3] = result[h-3] = amplitude * 1.2
		for (let i = 4; i < h-4; i++)
			result[i] = amplitude
		// mirror
		for (let i = 0; i < h; i++)
			result[h+i] = -result[h-i]

//			result[i] = -Math.sin((i / result.length) * 2 * Math.PI) * amplitude
		return result
	}

	// Converts uint8 buffer, tries to remove .TAP header(s) and / or split .853 files (returns array of uint8 buffer)
	// Will not be called by class.
	static FixFormat(buffer) {

		var kctap_header = [0xC3, 0x4B, 0x43, 0x2D, 0x54, 0x41, 0x50, 0x45, 0x20, 0x62, 0x79, 0x20, 0x41, 0x46, 0x2E, 0x20]
		var tap_find = function(element, index, array) {
  			for (let i = 0; i < kctap_header.length; i++)
  				if (array[index+i] !== kctap_header[i])
  					return false
  			return true
  		}
  		let pos = buffer.findIndex(tap_find) 
  		if (pos < 0)
  			return [buffer]
  		var result = []
  		
  		while (pos >= 0) {
  			buffer = buffer.slice(pos + 16)
  			pos = buffer.findIndex(tap_find)
  			let part = buffer.slice(0, pos < 0 ? undefined : pos)
  			let part_a = []
  			// Filter block numbers out
  			for (let i = 0; i < part.length; i++) {
  				if (i % 129 == 0)
  					console.log(part[i] + "> ")
  				else
  					part_a.push(part[i])
  			}
  			result.push(part_a)
  		}
  		return result
	}

	add_one() {
		this.audio.copyToChannel(this.one, 0, this.audio_pos); 
		this.audio_pos += this.one.length;
	}

	add_zero() {
		this.audio.copyToChannel(this.zero, 0, this.audio_pos); 
		this.audio_pos += this.zero.length;
	}

	add_stop() {
		this.audio.copyToChannel(this.stop, 0, this.audio_pos); 
		this.audio_pos += this.stop.length;
	}

	add_byte(b) {
		for (let bit = 0; bit < 8; bit++)
			if (b & (1 << bit))
				this.add_one()
			else
				this.add_zero()
		this.add_stop()
	}

	stop_play() {
		if (window.asource) {
			window.asource.stop()
			window.asource.disconnect()
		}
	}

	play() {
		this.stop_play()
		// Get an AudioBufferSourceNode.
		// This is the AudioNode to use when we want to play an AudioBuffer
		window.asource = this.ac.createBufferSource();
		// set the buffer in the AudioBufferSourceNode
		window.asource.buffer = this.audio;
		// connect the AudioBufferSourceNode to the
		// destination so we can hear the sound
		window.asource.connect(this.ac.destination);
		// start the source playing
		window.asource.start();
	}
}