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Hi!<br>
<br>
On 19.11.2010 05:33, Mathieu Bouchard wrote:
<blockquote
cite="mid:alpine.DEB.2.00.1011171151360.3984@paik.artengine.ca"
type="cite">On Wed, 17 Nov 2010, Martin Schied wrote:
<br>
<br>
<blockquote type="cite">did you speak about the "doppler"
distortion? true doppler distortion is harmonic for a single
sine wave, but not for 2 or more sines of different frequencies.
<br>
</blockquote>
<br>
Then can you explain what's wrong in my reasoning ? (the formulas
I wrote)
<br>
</blockquote>
no, sorry, I can't on the quick. but I know for sure that frequency
modulation only produces harmonics if the carrier and modulator are
in "simple" relations like 1:5 or your example 200 to 1000. <br>
<br>
The frequencies added by fm are multiples of the modulator added and
subtracted from the carrier. (carrier; 1000Hz, modulator 11Hz -->
pairs in order of strength: 989 + 1011, 978 + 1022 Hz ...)<br>
If you have frequencies going below 0Hz they wrap around the y=0Hz
axis. Result is a negative freuqency, or likewise the phase is
reversed. (for example 1000Hz modulated by 600Hz will have 200Hz in
the spectrum)<br>
<br>
If you use not-harmonic related frequencies like 320 and 1000 Hz and
you will have new frequencies which aren't multiples of 320 and
1000, but inbetween. (580 and 1320, ...), Also you will get
frequencies below the 320 Hz. However if you drive the modulation
very strong, a patten similar to a harmonic signal will appear,
possibly with a new base frequency, but also likely without.<br>
<br>
I'm absolutely not familiar with the case of a signal modulating
itself, but I'm pretty sure from experiments with your patch (or the
new I mad and attached) that there occur very similar (if not
identical) effects if you modulate a mix of 1000 + 320 Hz with
itself or you use separate carriers for 1000 and 320 Hz and
modulate them separately by the mix of 1000 + 320. I'm not sure if
this superposition is valid, but I'm pretty sure... at least it
sounds relatively similar if I do it in pd. The vd~ sounds always
"richer" possibly artifacts. (the spectrum looks very dirty too)<br>
<br>
<blockquote
cite="mid:alpine.DEB.2.00.1011171151360.3984@paik.artengine.ca"
type="cite">
<br>
<blockquote type="cite">I want to add that the vd~ approach is not
the "perfect implementation" for the above described frequency
modulatuon. the carrier is delayed against the modulating signal
a bit.
<br>
</blockquote>
<br>
You can add another [vd~] or [delread~] to fix that. I think I did
that in some other version of haut-parleur-doppler.pd, and if not,
I did similar things with other effects.
<br>
<br>
<blockquote type="cite">Like this it simulates a moving listener
instead a moving sound source.
<br>
</blockquote>
<br>
But there is no difference between a moving listener and a moving
source, apart from the wind.<br>
</blockquote>
there is. but for the low speeds of the cone we are simulating the
audible effects are not very different. (a moving sound source at
the speed of sound produces infinite frequency, a moving listener at
speed of sound hears only doubled frequency).<br>
<blockquote
cite="mid:alpine.DEB.2.00.1011171151360.3984@paik.artengine.ca"
type="cite">
<br>
What you mean is, regardless of whether it happens in the listener
or the source, the motion is out of phase with the actual signal.
<br>
<br>
</blockquote>
exactly and this is why I'd like to move the write head. How did
your correction using vd~ work?<br>
<blockquote
cite="mid:alpine.DEB.2.00.1011171151360.3984@paik.artengine.ca"
type="cite">
<br>
<blockquote type="cite">Unfortunately I don't know of such
externals already existing. However I don't expect the effects
being very different from the vd~ method.
<br>
</blockquote>
<br>
What if they aren't _any_ different ?
<br>
</blockquote>
it's only because of the slight delay I'd be interested to
eliminate. But as you also said I don't expect any big difference
between the delay free case and the vd~ case as the modulations
occuring with a slight off phase will not sound any different.
(however 2ms can be quite different for short percussive signals)<br>
<blockquote
cite="mid:alpine.DEB.2.00.1011171151360.3984@paik.artengine.ca"
type="cite">
<br>
<blockquote type="cite">A slow 20Hz sinewave modulating some high
frequencies will not sound very different if the 20Hz is delayed
or not. A 20 hz sound will have a duration which is much longer
that the delay.
<br>
</blockquote>
<br>
But it depends on the gain you choose. Suppose you have a
weapons-grade giant speaker, with a membrane of a few hectares...
<br>
<br>
I mean, play with the [*~] and you can get the delay variation to
be bigger than the period of a sinewave.<br>
</blockquote>
yep, that's also one of the effects I wanted to eliminate by the
moving write head.<br>
<br>
Martin<br>
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