[sdiy] Linear FM concept again

[Scott Gravenhorst]

hmmm.  "perceived" = average frequency.  I'm starting to get it...

Thanks, John.

This is sounding too easy, All I have to do is (cap coupled) mix an audio
freq. range output from one VCO with the linear CV of a linear VCO.

"John L Marshall" <john.l.marshall at gte.net> wrote:
>Scott,
>
>Exponential FM the perceived frequency goes up because we hear the average
>of the frequencies. For example: a carrier of 400 Hz modulated by 1 Volt
>will produce a swing from 200 Hz to 800 Hz. The average frequency will be
>500 Hz, not the original 400 Hz.
>
>Linear FM takes care of the problem. For example: a carrier of 400 Hz
>modulated by some voltage (Hmmm, Volts/Hertz) can produce a swing from 200
>Hz to 600 Hz. The average frequency will be 400 Hz, still.
>
>
>Take care,
>John
>---------------------------------------------------------------------------
>Pacific Northwest DIY Synthesizer meeting, July 20, 2002
>See: www.sound-photo.com
>---------------------------------------------------------------------------
>
>----- Original Message -----
>From: "Scott Gravenhorst" <music.maker at gte.net>
>To: <synth-diy at dropmix.xs4all.nl>
>Sent: Saturday, August 24, 2002 1:02 PM
>Subject: [sdiy] Linear FM concept again
>
>
>> What exactly is linear FM used for?  I'm trying to wrap my
>> head around this, but my brain is being stubborn.
>>
>> Here's how I understand it (which may be the whole problem):
>>
>> In a very simple example, linear FM seems usually
>> implemented by mixing a modulating signal such as another
>> VCO with a VCO's linear pitch CV input.  If the modulating
>> signal is of a constant amplitude, the effect on the
>> modulated VCO's output is to more widely change the pitch at
>> lower CVs.  When I use an LFO to modulate pitch, I usually
>> want the modulation in terms of cents to be the same, which
>> won't happen if the LFO is mixed with linear pitch CV.  (it
>> does work with an expo input)
>>
>> Why is this a good thing?
>>
>> Why wouldn't one want to FM into the expo input?
>>
>> I want to build some FM stuff for a linear synth, but not
>> understanding this is getting in the way of my design.
>>
>> =========================================================
>> - What good are laws that only lawyers understand?
>> - Government: The other religion.
>> - The media's credibility should always be questioned.
>> - Lambs who lie down with lions are lunch.
>>
>> -- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
>> -- Linux Rex         | RedWebMail by RedStarWare
>> -- FatMan: home1.GTE.NET/res0658s/FatMan/
>> -- NonFatMan: home1.GTE.NET/res0658s/electronics/
>>
>>
>

=========================================================  
- What good are laws that only lawyers understand?
- Government: The other religion.
- The media's credibility should always be questioned.
- Lambs who lie down with lions are lunch.

-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
-- Linux Rex         | RedWebMail by RedStarWare
-- FatMan: home1.GTE.NET/res0658s/FatMan/
-- NonFatMan: home1.GTE.NET/res0658s/electronics/