| ok, if i may, please allow me to further elicit details pertaining to the
second half of my question on fm synthesis, namely, how does csound deal
with modulation index? i'm re-reading old math notes in preparation to
attempt to understand your answers.
ar foscil xamp, kcps, kcar, kmod, kndx, ifn [,iphs]
kcar is carrier, kmod is modulator, kndx is index of modulation right?
now let's assign arbitrary values.
kcarrier C = 800 Hz
kmodulator M = 200 Hz
hold on, let's compute D, the frequency deviation (in Hz). But how? C - M =
absolute value of D??? in this case 600 Hz? If that were the case than kndx
would be predetermined by the values indicated for C and M because...
index of modulation I = D/M
I = 600/200
I = 3
now i've got to be missing something, or else it would only possible to
arbitrarily designate fixed values to two of the three variables kcar,
kmod, kndx. or maybe we create some wonderful sounding errors by forcing
equation to be false?
tolve
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To: Roger Klaveness , csound@maths.ex.ac.uk
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From: tolve
Subject: Re: mod index
Date: Fri, 20 Mar 1998 16:22:22 -0500
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First, my apologies to Curtis Roads who's explanation of modulation index
and bandwidth is crystal clear, though apparently not idiot proof.
i wrote...
>>>>>>>>>>>>>>>
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.
...
"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."
>>>>>>>>>>>>>>>>
he does go on to say:
"This is typical of many instruments... and is realized in FM by using
similar envelope shapes for both the carrier amplitude and index of
modulation."
the only suggestion i could make would be for this to be stated a couple of
lines sooner on the previous page.
i'm sure this is not the last time i will embarrass myself on this list.
and towards that end, i have posted two more questions under separate cover.
hope i didn't unduly confuse anyone who already understood this topic.
tolve
>>had to read your answers a couple of times, but seems that all of them, and
>>the book are correct, although they sound different. interesting.
>>
>>thanks guys!
>>tolve
>>
>>
>>
>Maybe I'm wrong, but........
>After thinking a little about it it seems to me that the amount of frequency
>deviation (D)
>is the same as the amplitude of the modulator.
>So I think the book is rigth, if one asumes that the amplitude of the
>modulator follows the
>amplitude of the instrument.
>
>----------------------------------------------------------------------------
>Roger Klaveness
>roger@apas.no
>----------------------------------------------------------------------------,
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From: tolve
Subject: messing with phase
Date: Fri, 20 Mar 1998 16:22:31 -0500
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say i want to create two identical sine waves with identical start times,
but with one slightly out of phase with the other. i know that i can
accomplish this by starting one in advance of the other but keeping it
silent until the start time of the other.
is there not a more elegant way to do the job?
tolve
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Subject: Re: mod index variables
To: Csound mailing list
Date: Fri, 20 Mar 1998 17:09:26 -0500 (EST)
From: Eli Brandt
In-Reply-To: from "tolve" at Mar 20, 98 04:22:28 pm
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tolve wrote:
> ar foscil xamp, kcps, kcar, kmod, kndx, ifn [,iphs]
> now i've got to be missing something, or else it would only possible to
> arbitrarily designate fixed values to two of the three variables kcar,
> kmod, kndx.
kmod controls the modulator's frequency, kndx its amplitude.
e
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Date: Fri, 20 Mar 1998 14:21:27 -0800 (PST)
From: "Matt J. Ingalls"
To: tolve
Cc: csound@maths.ex.ac.uk
Subject: Re: messing with phase
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use 2 gen 9s
-matt
On Fri, 20 Mar 1998, tolve wrote:
> say i want to create two identical sine waves with identical start times,
> but with one slightly out of phase with the other. i know that i can
> accomplish this by starting one in advance of the other but keeping it
> silent until the start time of the other.
>
> is there not a more elegant way to do the job?
>
> tolve
>
>
>
>
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From: Hans Mikelson
To: csound@maths.ex.ac.uk, tolve
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Subject: Re: messing with phase
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-----Original Message-----
From: tolve
To: csound@maths.ex.ac.uk
Date: Friday, March 20, 1998 3:30 PM
Subject: messing with phase
>but with one slightly out of phase with the other
; Amp Fqc Wave Phase
a1 oscil iamp, ifqc, 1
a2 oscil iamp, ifqc, 1, .0001
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To: Kim Cascone , Eli Brandt
From: tolve
Subject: Re: mod index variables
Cc: csound@maths.ex.ac.uk
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kim & eli,
this last salvo has cleared the smoke a bit:
deviation index measures the difference between the lowest and highest
*sideband.* the result of M modulating C. and kndx controls the amplitude
of M which determines the number of sidebands generated. duh. therefore C -
M is *not* the operative deviation here. blind alley.
thanks!
tolve
>if you think of deviation in this (analog) way:
>- you have a sinewave osc (freq=f1...let's say this is 1kHz)
>- you have another sinewave osc (f2 and let's say this is 1Hz) feeding into
>the vc freq input
>- the vc input to osc f1 has an attenuator
>- the attenuator is set to zero
>- as you increase the attenuator f1 starts to "warble" (frequency modulate)
>- the osc generating f1 is now being told to go from a lower freq to a
>higher freq in a smooth sinewave like motion
>- so let's assume I rasied the attenuator enough to give me a deviation
>between 900Hz -> 1100 (above and below the 1kHz freq)...
>- the higher freq (1100kHz) - the lower freq (900Hz) is the deviation
>- D = 200Hz where D is deviation
>- and since the modulating osc is set to 1Hz
>- index = d/m = 200/1 =200
>does this help clear it up or did I explain the wrong aspect to your question?
>hope this helps
>:)
>KIM
>
>
>______________________________
><> kim.cascone <>
><> sound.designer -- headspace <>
><> anechoic@sirius.com <>
><>http://www.sirius.com/~anechoic<>
><><><><><><><><><><><><><><><><>
> :: "blueCube( )" :: kim.cascone ::
> [release date: spring 98, label: Rastermusic]
>_________________________________________
>"the meta-designer creates context, not content"
> -- Gene Youngblood
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