Re: [LAU] Subject: Albums under a label recorded and/or mixed with Linux

Moved to LAD as this is getting outside the normal discussion on LAU.

On Sun, September 26, 2010 6:12 am, fons@email-addr-hidden wrote:
> On Sun, Sep 26, 2010 at 05:50:24AM -0700, Patrick Shirkey wrote:
>
>> Can you give me a little more idea why you feel using FFT in this method
>> is more likely to return atrifacts than the equivalent convolution? Is
>> it
>> simply because there is more data being crunched to get to the end
>> result?
>
> Again, the choice is not between 'FFT' and 'convolution'. Jamin
> performs convolution, and uses an FFT to do it. The problem is
> that what Jamin does is *cyclic* convolution which produces
> artefacts and is not the same as filtering. Filtering requires
> *linear* convolution, which would actually be simpler, if you
> take into account the steps that Jamin takes to reduce the ill
> effects of the cyclic convolution.
>
> As explained above, the difference is in step (6) which for
> cyclic convolution is allowed to wrap around (meaning that
> part of the output ends up where it shouldn't be), while
> in linear convolution this is avoided by limiting the size
> of the inputs. Unless you want the detailed maths I don't
> think I could explain it any more clearly.
>

I have it on good authority that all linear convolution operations can be
expressed in the transformed domain, and vice versa. There is no
difference except for clarity of presentation and sometimes some specific
implementation issues.

So it might be a worthwhile exercise to present the math behind your
reasoning. We should probably move that discussion to the LAD list though.

Cheers.

-- 
Patrick Shirkey
Boost Hardware Ltd.
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