AW(Andre): [sdiy] analogue phase modulation

[Andre Majorel]

On 2007-01-11 20:19 +0100, JH. wrote:

> Would be interesting to know the OL number for MI of 3.14, if it's
> explicitly given in that table.

For the DX21/DX27/DX100, output level 75 is MI 3.143.

For the DX7, here are the surrounding values :

OL	MI
75	1.639
80	2.512
85	3.894
90	6.029

> > The modulation index is defined on page 56 as delta_f / f_m where
> > delta_f is the frequency deviation above and below the average
> > frequency of the carrier and f_m is the modulating frequency.
> 
> ... and that _relative_ frequency deviation (delta_f / f_m) is
> identically equal to the _absolute_ phase deviation, isn't it? So those
> same MI numbers directly describe what I've been looking for: the phase
> excursion (in radiants), caused by the modulation.

Uh... I'll take your word for it. :-)

If you need more information, the book is available online :

  http://www.spoogeworld.com/music/instruments/yamaha/fm_theory_and_applications.pdf

Besides output levels and modulation indices, appendix 2 also
gives TL TL/8, X and 2**X but don't ask me what those represent.

If you have problems reading the scan, I have the book.

There's plenty more on :

  http://www.spoogeworld.com/music/instruments/yamaha/main.php

-- 
André Majorel <URL:http://www.teaser.fr/~amajorel/>
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