Repository: incubator-guacamole-client Updated Branches: refs/heads/master cc9af8ed2 -> a6ccb36bd
GUACAMOLE-25: Migrate to Lanczos interpolation (a = 3). Project: http://git-wip-us.apache.org/repos/asf/incubator-guacamole-client/repo Commit: http://git-wip-us.apache.org/repos/asf/incubator-guacamole-client/commit/c1373129 Tree: http://git-wip-us.apache.org/repos/asf/incubator-guacamole-client/tree/c1373129 Diff: http://git-wip-us.apache.org/repos/asf/incubator-guacamole-client/diff/c1373129 Branch: refs/heads/master Commit: c137312963aa084b54b46b8ffaa710971be5b24d Parents: 0c0ee96 Author: Michael Jumper <[email protected]> Authored: Sun May 1 00:23:15 2016 -0700 Committer: Michael Jumper <[email protected]> Committed: Mon May 23 15:00:00 2016 -0700 ---------------------------------------------------------------------- .../src/main/webapp/modules/AudioRecorder.js | 84 +++++++++++++++++--- 1 file changed, 75 insertions(+), 9 deletions(-) ---------------------------------------------------------------------- http://git-wip-us.apache.org/repos/asf/incubator-guacamole-client/blob/c1373129/guacamole-common-js/src/main/webapp/modules/AudioRecorder.js ---------------------------------------------------------------------- diff --git a/guacamole-common-js/src/main/webapp/modules/AudioRecorder.js b/guacamole-common-js/src/main/webapp/modules/AudioRecorder.js index 38e2cad..1f7c83d 100644 --- a/guacamole-common-js/src/main/webapp/modules/AudioRecorder.js +++ b/guacamole-common-js/src/main/webapp/modules/AudioRecorder.js @@ -127,6 +127,17 @@ Guacamole.RawAudioRecorder = function RawAudioRecorder(stream, mimetype) { var BUFFER_SIZE = 512; /** + * The window size to use when applying Lanczos interpolation, commonly + * denoted by the variable "a". + * See: https://en.wikipedia.org/wiki/Lanczos_resampling + * + * @private + * @contant + * @type Number + */ + var LANCZOS_WINDOW_SIZE = 3; + + /** * The format of audio this recorder will encode. * * @private @@ -219,11 +230,64 @@ Guacamole.RawAudioRecorder = function RawAudioRecorder(stream, mimetype) { var processor = null; /** + * The normalized sinc function. The normalized sinc function is defined as + * 1 for x=0 and sin(PI * x) / (PI * x) for all other values of x. + * + * See: https://en.wikipedia.org/wiki/Sinc_function + * + * @private + * @param {Number} x + * The point at which the normalized sinc function should be computed. + * + * @returns {Number} + * The value of the normalized sinc function at x. + */ + var sinc = function sinc(x) { + + // The value of sinc(0) is defined as 1 + if (x === 0) + return 1; + + // Otherwise, normlized sinc(x) is sin(PI * x) / (PI * x) + var piX = Math.PI * x; + return Math.sin(piX) / piX; + + }; + + /** + * Calculates the value of the Lanczos kernal at point x for a given window + * size. See: https://en.wikipedia.org/wiki/Lanczos_resampling + * + * @private + * @param {Number} x + * The point at which the value of the Lanczos kernel should be + * computed. + * + * @param {Number} a + * The window size to use for the Lanczos kernel. + * + * @returns {Number} + * The value of the Lanczos kernel at the given point for the given + * window size. + */ + var lanczos = function lanczos(x, a) { + + // Lanczos is sinc(x) * sinc(x / a) for -a < x < a ... + if (-a < x && x < a) + return sinc(x) * sinc(x / a); + + // ... and 0 otherwise + return 0; + + }; + + /** * Determines the value of the waveform represented by the audio data at * the given location. If the value cannot be determined exactly as it does * not correspond to an exact sample within the audio data, the value will * be derived through interpolating nearby samples. * + * @private * @param {Float32Array} audioData * An array of audio data, as returned by AudioBuffer.getChannelData(). * @@ -241,17 +305,19 @@ Guacamole.RawAudioRecorder = function RawAudioRecorder(stream, mimetype) { // Convert [0, 1] range to [0, audioData.length - 1] var index = (audioData.length - 1) * t; - // Get the closest whole integer samples indices - var left = Math.floor(index); - var right = Math.ceil(index); + // Determine the start and end points for the summation used by the + // Lanczos interpolation algorithm (see: https://en.wikipedia.org/wiki/Lanczos_resampling) + var start = Math.floor(index) - LANCZOS_WINDOW_SIZE + 1; + var end = Math.floor(index) + LANCZOS_WINDOW_SIZE; - // Pull the values of the closest samples - var leftValue = audioData[left]; - var rightValue = audioData[right]; + // Calculate the value of the Lanczos interpolation function for the + // required range + var sum = 0; + for (var i = start; i <= end; i++) { + sum += (audioData[i] || 0) * lanczos(index - i, LANCZOS_WINDOW_SIZE); + } - // Determine the value of the sample at the given non-integer location - // through linear interpolation of the nearest samples - return leftValue + (rightValue - leftValue) / (right - left) * (index - left); + return sum; };
