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Re: AW: AW: [Doepfer_a100] discontinuation of all modules with CEM3320, CEM3340 and CEM3381/PA381

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  • Florian Anwander
    Hi ... The theoretically resulting waveform of FM is only real for the core wave form. All other waveforms will be that, what the waveform converter produces
    Message 1 of 51 , Aug 1, 2008
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      Hi

      > Is it? What's the difference between the effect of having different
      > cores?
      The theoretically resulting waveform of FM is only "real" for the core
      wave form. All other waveforms will be that, what the waveform converter
      produces from the fm'ed core-waveform.


      I uploaded two graphic files to the files section:
      http://launch.groups.yahoo.com/group/Doepfer_a100/files/analog-fm/
      These are excerpts from my book.

      I some months ago wrote the following text in private mail to Bakis,
      which explains the images:
      -----------------------snip------------------

      The most relevant thing is: FM with analogue VCOs has nothing to do with
      the theoretical FM, because everything depends on the working principle
      of the core oscillator (saw or triangle), and what the waveformconvertes
      make out of the fm'ed core wave form.

      I'll attach two excerpts from my book:
      analogue_fm.png explains what really happens in a saw based VCO. Left is
      an log FM, right is the linear FM:

      * the first row (rectangle) is the modulator with an amount of +1V to -1V

      * the second row (400Hz saw) is the carrier

      * the third row shows the two saws which would be created by a CV of +1V
      and -1V. In log FM this will be 1V up/down => 1 Octave up/down, =>
      800Hz/200Hz. In lin FM this will be 1V a certain frequency up/down, =>
      lets say 200 HZ => 600Hz/200Hz. The higher result(800Hz or 600Hz) is
      light grey; the lower result (200Hz) is dark grey. The two frequencies
      look like two ramps with different steepness.


      * Now the fourth line shows what really happens in the VCO: There is a
      thin horizontal line, which is the threshold at which the Capacitor in
      the core-oscillator is unloaded.
      The rectangle switches between the two steepnesses. With the bigger
      steepness of the 800Hz at the log FM the resulting wave form will reach
      the threshold faster than with the "600Hz-steepness". As you can see the
      threshold will be reached at the same time as with the original
      carrier signal.

      Thats the one graphic.


      The second graphic shows, the same FM, but this time not the core saw
      oscillator, but the output of different wave forms from the waveform
      converter. The Modulator still is the known rectangle.
      Line a shows what we would expect for a triangle carrier.
      Line b shows what we would expect for a rectangle carrier.
      Line c shows what we really will get at the triangle output.
      Line d shows what we really will get at the rectangle output.

      The latter two show, what the waveform converter will create from the
      originally FM'ed saw from the core-oscillator. Here you can see that
      this has nothing to do with real FM
      -----------------------snip------------------
    • hardware@doepfer.de
      I should read your books more carefully :-) Dieter
      Message 51 of 51 , Aug 4, 2008
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        I should read your books more carefully :-)

        Dieter


        > -----Ursprungliche Nachricht-----
        > Von: Doepfer_a100@yahoogroups.com
        > [mailto:Doepfer_a100@yahoogroups.com]Im Auftrag von Florian Anwander
        > Gesendet: Freitag, 1. August 2008 11:17
        > An: Doepfer_a100@yahoogroups.com
        > Betreff: Re: AW: AW: [Doepfer_a100] discontinuation of all modules with
        > CEM3320, CEM3340 and CEM3381/PA381
        >
        >
        > Hi
        >
        > > Is it? What's the difference between the effect of having different
        > > cores?
        > The theoretically resulting waveform of FM is only "real" for the core
        > wave form. All other waveforms will be that, what the waveform converter
        > produces from the fm'ed core-waveform.
        >
        >
        > I uploaded two graphic files to the files section:
        > http://launch.groups.yahoo.com/group/Doepfer_a100/files/analog-fm/
        > These are excerpts from my book.
        >
        > I some months ago wrote the following text in private mail to Bakis,
        > which explains the images:
        > -----------------------snip------------------
        >
        > The most relevant thing is: FM with analogue VCOs has nothing to do with
        > the theoretical FM, because everything depends on the working principle
        > of the core oscillator (saw or triangle), and what the waveformconvertes
        > make out of the fm'ed core wave form.
        >
        > I'll attach two excerpts from my book:
        > analogue_fm.png explains what really happens in a saw based VCO. Left is
        > an log FM, right is the linear FM:
        >
        > * the first row (rectangle) is the modulator with an amount of +1V to -1V
        >
        > * the second row (400Hz saw) is the carrier
        >
        > * the third row shows the two saws which would be created by a CV of +1V
        > and -1V. In log FM this will be 1V up/down => 1 Octave up/down, =>
        > 800Hz/200Hz. In lin FM this will be 1V a certain frequency up/down, =>
        > lets say 200 HZ => 600Hz/200Hz. The higher result(800Hz or 600Hz) is
        > light grey; the lower result (200Hz) is dark grey. The two frequencies
        > look like two ramps with different steepness.
        >
        >
        > * Now the fourth line shows what really happens in the VCO: There is a
        > thin horizontal line, which is the threshold at which the Capacitor in
        > the core-oscillator is unloaded.
        > The rectangle switches between the two steepnesses. With the bigger
        > steepness of the 800Hz at the log FM the resulting wave form will reach
        > the threshold faster than with the "600Hz-steepness". As you can see the
        > threshold will be reached at the same time as with the original
        > carrier signal.
        >
        > Thats the one graphic.
        >
        >
        > The second graphic shows, the same FM, but this time not the core saw
        > oscillator, but the output of different wave forms from the waveform
        > converter. The Modulator still is the known rectangle.
        > Line a shows what we would expect for a triangle carrier.
        > Line b shows what we would expect for a rectangle carrier.
        > Line c shows what we really will get at the triangle output.
        > Line d shows what we really will get at the rectangle output.
        >
        > The latter two show, what the waveform converter will create from the
        > originally FM'ed saw from the core-oscillator. Here you can see that
        > this has nothing to do with real FM
        > -----------------------snip------------------
        >
        > ------------------------------------
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