regarding FM spectrum (# of sidebands)
p229 Curtis Roads Computer Music Tutorial pub MIT.

index of modulation I is defined as

I=D/M
where D is the amount of frequency deviation (in Hz).
if D is 100 Hz and Modulator M is 100 Hz, then the index of modulation is 1.0.

fine, I is determined by two frequency values.
but then he goes on to say:
"because the bandwidth increases as the index of modulation increases, FM
can simulate an important property of instrumental tones. Namely, as the
amplitude increases, so does the bandwidth."

huh? who said anything about amplitude? suppose he means that amplitude
must be somehow indexed to a change in pitch of the modulator to achieve
this affect?

could someone please clarify? and how does csound deal with this?

tolve

At 5:40 PM -0500 3/19/98, tolve wrote:
>regarding FM spectrum (# of sidebands)
>p229 Curtis Roads Computer Music Tutorial pub MIT.
>"because the bandwidth increases as the index of modulation increases, FM
>can simulate an important property of instrumental tones. Namely, as the
>amplitude increases, so does the bandwidth."

If your modulation index control signal (which should be at sr not kr
regardless of what stupid things foscil does) tracks with your note
envelope (something you have to arrange e.g. afmindex = aenv*0.001) then
the harmonic content increases as the volume increases. Of course, you can
have seperate mod-index and amplitude envelopes, but then you have to
decide in what fashion the harmonic content should change over time.

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