Bug 135986

Summary: wrong normalization in RealtimeAnalyser.cpp
Product: WebKit Reporter: wothke <info>
Component: Web AudioAssignee: Nobody <webkit-unassigned>
Status: RESOLVED DUPLICATE    
Severity: Normal CC: crogers
Priority: P2    
Version: 528+ (Nightly build)   
Hardware: Unspecified   
OS: Unspecified   
URL: In order to understand the idiotic differences between the data ranges of the AnalyzerNode's getFloatFrequencyData() and getByteFrequencyData() APIs I finally found myself analyzing the WebKit sources: https://github.com/WebKit/webkit/blob/master/Source/WebCore/Modules/webaudio/RealtimeAnalyser.cpp

Description wothke 2014-08-15 11:09:53 PDT 
In order to understand the idiotic differences between the data ranges of the AnalyzerNode's getFloatFrequencyData() and getByteFrequencyData() APIs I finally found myself analyzing the WebKit sources: https://github.com/WebKit/webkit/blob/master/Source/WebCore/Modules/webaudio/RealtimeAnalyser.cpp

What surprises me there is the:
    const double magnitudeScale = 1.0 / DefaultFFTSize;
which is used to normalize the FFT results (see RealtimeAnalyser::doFFTAnalysis()).

I am not an expert on FFT but I think the correct scaling factor rather be: 2/actualFftSize

Also it seems that the respective code has actually been fixed in Chromium! see chromium\src\third_party\WebKit\Source\modules\webaudio
Comment 1 Alexey Proskuryakov 2014-08-20 17:54:04 PDT 

*** This bug has been marked as a duplicate of bug 136120 ***