# [PD] fft beginner question

Thomas Mayer thomas at dergrossebruder.org
Tue Nov 20 17:22:30 CET 2007

```Chuckk Hubbard wrote:
> On Nov 20, 2007 5:39 PM, Frank Barknecht <fbar at footils.org> wrote:
>> For some calculations polar, for others cartesian coordinates are
>> easier to use. To quote Miller:
>>
>>   The main reason we use complex numbers in electronic music is
>>   because they magically automate trigonometric calculations. We
>>   frequently have to add angles together in order to talk about the
>>   changing phase of an audio signal as time progresses (or as it is
>>   shifted in time, as in this chapter). It turns out that, if you
>>   multiply two complex numbers, the argument of the product is the sum
>>   of the arguments of the two factors.
>
> I still don't exactly understand why one couldn't just use (x, y)
> vectors; why the y value has to be multiplied by something imaginary.
> I mean, i/j is *defined as* the square root of -1, but it can't really
> *be* the square root of -1...  I've accepted it and moved on to more
> practical questions, but that is still mysterious for me.

Everything in mathematics *is* so if *definined*. You could define your
own mathematics by saying "there are no two straight lines that do not
subtend" (no parallels). In fact, Riemann did so, and has created a
geometry different from Euklidean, which is the basis for calculation on
a sphere (straight lines -> great circles).

<http://en.wikipedia.org/wiki/Non-Euclidean_geometry>

It does not matter, if it stresses your personal "experience", as long
Negative numbers were a great problem to mathematicians as well:

European mathematicians however, for the most part, resisted the concept
of negative numbers until the 17th century, although Fibonacci allowed
negative solutions in financial problems where they could be interpreted
as debits (chapter 13 of Liber Abaci, 1202) and later as losses (in
Flos). At the same time, the Chinese were indicating negative numbers by
drawing a diagonal stroke through the right-most non-zero digit. The
first use of negative numbers in a European work was by Chuquet during
the 15th century. He used them as exponents, but referred to them as
“absurd numbers”.

<http://en.wikipedia.org/wiki/Negative_and_non-negative_numbers#First_usage_of_negative_numbers>

cu Thomas
--
"Prisons are needed only to provide the illusion that courts and police
are effective. They're a kind of job insurance."
(Leto II. in: Frank Herbert, God Emperor of Dune)
http://thomas.dergrossebruder.org/

```