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/*! |
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* bitdepth |
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* Change the bit depth of audio samples to and from 8, 16, 24, 32, 32 IEEE & 64-bit. |
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* Copyright (c) 2017 Rafael da Silva Rocha. MIT License. |
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* https://github.com/rochars/bitdepth |
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* |
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*/ |
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/** |
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* Max number of different values for each bit depth. |
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* @enum {number} |
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*/ |
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const BitDepthMaxValues = { |
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8: 256, |
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16: 65536, |
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16
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24: 16777216, |
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32: 4294967296 |
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}; |
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/** |
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* Change the bit depth of the data. |
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* The input array is modified in-place. |
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* @param {!Array<number>} data The data. |
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* @param {string} originalBitDepth The original bit depth of the data. |
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* One of "8", "16", "24", "32", "32f", "64" |
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* @param {string} targetBitDepth The new bit depth of the data. |
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* One of "8", "16", "24", "32", "32f", "64" |
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*/ |
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function toBitDepth(data, originalBitDepth, targetBitDepth) { |
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if (originalBitDepth == targetBitDepth) { |
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return; |
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} |
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validateBitDepths(originalBitDepth, targetBitDepth); |
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let len = data.length; |
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for (let i=0; i<len; i++) { |
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// 8-bit samples are unsigned; |
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// They are signed here before conversion |
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// (other bit depths are all signed) |
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data[i] = sign8Bit(data[i], originalBitDepth); |
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// If it is a float-to-float or int-to-float conversion then |
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// the samples in the target bit depth will be normalized in the |
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// -1.0 to 1.0 range; there is no need to multiply |
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if (targetBitDepth == "32f" || targetBitDepth == "64") { |
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data[i] = toFloat(data[i], originalBitDepth); |
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// If it is a float-to-int or int-to-int conversion then the |
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// samples will be de-normalized according to the bit depth |
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}else { |
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data[i] = toInt(data[i], originalBitDepth, targetBitDepth); |
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} |
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} |
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} |
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/** |
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* Sign unsigned 8-bit data. |
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* @param {number} sample The sample. |
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* @param {string} originalBitDepth The original bit depth of the data. |
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* One of "8", "16", "24", "32", "32f", "64" |
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*/ |
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function sign8Bit(sample, originalBitDepth) { |
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if (originalBitDepth == "8") { |
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sample -= 128; |
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} |
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return sample; |
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} |
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/** |
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* Unsign signed 8-bit data. |
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* @param {number} sample The sample. |
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* @param {string} targetBitDepth The target bit depth of the data. |
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* One of "8", "16", "24", "32", "32f", "64" |
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*/ |
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function unsign8Bit(sample, targetBitDepth) { |
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if (targetBitDepth == "8") { |
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sample += 128; |
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} |
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return sample; |
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} |
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/** |
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* Change the bit depth from int to float. |
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* The input array is modified in-place. |
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* @param {number} sample The sample. |
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* @param {string} originalBitDepth The original bit depth of the data. |
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* One of "8", "16", "24", "32", "32f", "64" |
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*/ |
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function toFloat(sample, originalBitDepth) { |
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let oldMaxValue = parseInt((BitDepthMaxValues[originalBitDepth]) / 2, 10); |
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if (originalBitDepth != "32f" && originalBitDepth != "64") { |
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if (sample > 0) { |
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sample = sample / (oldMaxValue - 1); |
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} else { |
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sample = sample / oldMaxValue; |
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} |
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} |
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return sample; |
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} |
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/** |
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* Change the bit depth of the data. |
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* The input array is modified in-place. |
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* @param {number} sample The sample. |
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* @param {string} originalBitDepth The original bit depth of the data. |
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* One of "8", "16", "24", "32", "32f", "64" |
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* @param {string} targetBitDepth The new bit depth of the data. |
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* One of "8", "16", "24", "32", "32f", "64" |
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*/ |
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function toInt(sample, originalBitDepth, targetBitDepth) { |
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// If the original samples are float, then they are already |
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// normalized between -1.0 and 1.0; All that is need is to |
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// multiply the sample values by the new bit depth max value |
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let oldMaxValue = parseInt((BitDepthMaxValues[originalBitDepth]) / 2, 10); |
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let newMaxValue = parseInt((BitDepthMaxValues[targetBitDepth]) / 2, 10); |
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if (originalBitDepth == "32f" || originalBitDepth == "64" ) { |
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if (sample > 0) { |
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sample = sample * (newMaxValue - 1); |
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} else { |
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sample = sample * newMaxValue; |
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} |
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// If the original samples are integers, then they need to be |
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// divided by the maximum values of its original bit depth |
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// (to normalize them between -1.0 and .10) and then multiply |
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// them by the new bit depth max value |
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} else { |
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if (sample > 0) { |
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sample = |
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parseInt((sample / (oldMaxValue - 1)) * newMaxValue - 1, 10); |
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} else { |
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sample = parseInt((sample / oldMaxValue) * newMaxValue, 10); |
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} |
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} |
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// Make the samples unsigned if the target bit depth is "8" |
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return unsign8Bit(sample, targetBitDepth); |
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} |
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/** |
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* Validate the bit depth. |
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* @param {string} originalBitDepth The original bit depth. |
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* Should be one of "8", "16", "24", "32", "32f", "64". |
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* @param {string} targetBitDepth The target bit depth. |
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* Should be one of "8", "16", "24", "32", "32f", "64". |
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* @throws {Error} If any argument does not meet the criteria. |
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*/ |
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function validateBitDepths(originalBitDepth, targetBitDepth) { |
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let validBitDepths = ["8", "16", "24", "32", "32f", "64"]; |
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if (validBitDepths.indexOf(originalBitDepth) == -1 || |
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validBitDepths.indexOf(targetBitDepth) == -1) { |
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throw new Error("Invalid bit depth."); |
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} |
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return true; |
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} |
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module.exports.toBitDepth = toBitDepth; |
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module.exports.BitDepthMaxValues = BitDepthMaxValues; |
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rochars /
bitdepth
