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Re: [Bug 21980] New: WaveTable is highly underspecified

From: Joseph Berkovitz <joe@noteflight.com>
Date: Thu, 9 May 2013 16:11:06 -0400
Cc: Ehsan Akhgari <ehsan.akhgari@gmail.com>, "public-audio@w3.org WG" <public-audio@w3.org>
Message-Id: <4B86429C-EBB7-4658-9232-F5543C1B6C7A@noteflight.com>
To: Russell McClellan <russell@motu.com>
I agree that if the reference to "imaginary" were removed from the spec, this might be much clearer. Depending on how one thinks of the Fourier series in terms of complex numbers, one can come up with conflicting ideas on the sign of the B coefficient.

If we're just saying that the arrays' elements with index n are the real coefficients of the real functions cos(nt) and sin(nt), that's seems clearer to me.

…joe

> The only part that seems at all unclear is listing the imaginary array as "an array of sine terms".  Traditionally the real and imaginary parts together represent the magnitude and phase of the complex wave at that bin, and angles traditionally move up as time moves forward, which would make the imaginary array an array of *negative* sine coefficients, if you have to give it a real interpretation.  A user just reading the spec may be surprised to find that putting a coefficient of 1 on the first sine term will produce an output pi radians phase shifted from what she or he had expected.  This is a minor point.
> 
> Thanks,
> -Russell
Received on Thursday, 9 May 2013 20:11:36 UTC

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