[sdiy] semi ot: convolution and ringmodulation : interested? & help

[Larry]

Martin

It looks interesting, and I think I may play with it once my current batch 
of modules is completed.

I noticed that you do not want commercial use of your software.  I might 
suggest that you look at the Gnu Public License (GPL), this is a copyright 
that has provisions for the use of your software, but maintains the credits 
to the authors, and requires that any modifications to the source code also 
be released to the public.  Here is the web page for it:

http://www.gnu.org/copyleft/gpl.html

Larry Troth

At 02:17 PM 10/9/01 +0200, Czech Martin wrote:
>I did not solder much this year (1), but I did some very interesting C
>programming. One activity came out as a convolution tool.
>Read more here:
>
>http://www.geocities.com/SoHo/Museum/4459/software_em/fact.html
>
>It was not so easy for me to program this. It was even more difficult
>to use this in the context of my pieces.
>I have composed two pieces for my 4th CD using this technique.
>Especially the convolution of rather long sequences is interesting.
>Other research (reverb) is ongoing, I will not tell here, but
>the results will be interesting for sure.
>
>The other one is brandnew. I needed ringmodulation for the CD and also
>for the performance of my tape music instantly. So there was pressure.
>I finally came up within 6 days with this C code.
>It is a discrete implementation of a so called "ring modulator",
>or -as we say- 4 quadrant multiplier. If you do this in discrete
>domain, it is not just multiplication, since you must make sure that
>the side bands will not get aliased. Thus internal sample rate conversion
>is involved, leading to the fact that for any pair of input samples
>hundreds of multiplications and additions have to be made.
>Of course the code is optimised, so that unnecessary  high sample
>rate operations are avoided. On my slugish 100MHz Pentium
>it will take 2x the playing time, you see how this will go
>with a  1GHz machine. Of course, the output is automatically
>normalised to 16 bit (same as in FACT), so application
>is a real no brainer. Input sample quality should be good,
>garbage in, garbage out. This applies especially to spurious
>DC offset (ADC).
>
>I think it is interesting that one can hear almost ideal multiplication
>without nonlinearities or noise. Caveat: analog systems can modulate
>with 20kHz or 40kHz and higher, thus effectively shifting both
>sidebands out of audio range. This will obviously not work for
>44.1 kHz sample rate input. I didn't need that so far, but
>the remedy is straight forward. It can be done.
>Another thing is pitch tracking. It would be interesting to track
>the modulator with the incomming programme signal.
>So there is some work to be done...
>
>If there is any interest I can put the source on my site.
>
>
>Some people complained that I gave no executeables, or executeables
>with rather long dynamic linked libs. This is correct.
>Is there anybody out there who could compile these sources for
>DOS or MacOS without any lengthy DLLs?
>
>m.c.
>
>(1): if the new girlfriend issue runs hot, the iron will stay cold
>very simple. Remember my bitter remarks in spring? A real hate/love affair.
>All has settled now. I guess I will be married in 2002.
>But I should point out that it is my problem if I'm not able to do
>anything due to psycho stress, not hers.
>
>m.c.