17403 2012-06-05 12:28:55 +0000 (LinearConvolution): Linear convolution effect is defined by Wikipedia 2014-10-28 17:16:39 +0000 1 1 1 Unclassified AudioWG Web Audio API unspecified PC All CLOSED WONTFIX P2 normal TBD 1 mike crogers mage ot public-audio dave.null oldest_to_newest 68715 0 mike 2012-06-05 12:28:55 +0000 Audio-ISSUE-69 (LinearConvolution): Linear convolution effect is defined by Wikipedia [Web Audio API] http://www.w3.org/2011/audio/track/issues/69 Raised by: Philip Jägenstedt On product: Web Audio API https://dvcs.w3.org/hg/audio/raw-file/tip/webaudio/specification.html#ConvolverNode links to https://dvcs.w3.org/hg/audio/raw-file/tip/webaudio/specification.html#Convolution-section links to http://en.wikipedia.org/wiki/Convolution The definition should be in the specification itself. A problem that is not addressed at all is how phase/latency depends on the length of the convolution buffer. In other words, it must be defined exactly how each sample value is calculated from the the input signal and the impulse response buffer. 68784 1 olivier.thereaux 2012-06-07 08:17:23 +0000 [admin] Assigning items currently being worked on by editor. 68891 2 crogers 2012-06-09 00:06:34 +0000 I believe the operation "linear convolution" is a sufficiently well-known and well-defined operation in mathematics that no further explanation is required, anymore than the definition of a cos() function. It is defined in many texts on math/DSP. I will add an "informative" link to a page which can help guide implementors to practically implement this well-defined mathematical operation. I am happy also to point to working, cross-platform, well-optimized code having a non-restrictive license. I can also point to an alternate implementation "Freeverb": http://freeverb3.sourceforge.net/ FIXED: https://dvcs.w3.org/hg/audio/rev/7865f8b76f19 68952 3 mage 2012-06-12 08:43:52 +0000 I think this mail-comment from the original issue was overlooked: " The new document [1] contains valuable information, but isn't what this issue was about. If linear convolution need not be defined, then the issue should be closed as invalid. Not everyone reading the spec will have a background in signal processing, e.g. we want our QA to be able to write tests with little effort. We suggest to define the output y in terms of the input x and the [possibly normalized] impulse response g as a summation formula or pseudo-code such as: y[n] = 0 for i in 0...N-1: y[n] += x[n-i] * g[i] This leaves no room for ambiguity about the phase of the output signal. ISSUE-70 will need to be resolved for the above formula to make sense, though, as the input and impulse response may have different numbers of channels. [1] https://dvcs.w3.org/hg/audio/raw-file/tip/webaudio/convolution.html " 113867 4 olivier.thereaux 2014-10-28 17:13:47 +0000 Web Audio API issues have been migrated to Github. See https://github.com/WebAudio/web-audio-api/issues 114010 5 olivier.thereaux 2014-10-28 17:16:39 +0000 Closing. See https://github.com/WebAudio/web-audio-api/issues for up to date list of issues for the Web Audio API.