[sdiy] Why is Linear FM usually (always?) AC Coupled?

Frédéric (Opensource) marzacdev at gmail.com
Tue Feb 4 13:00:47 CET 2020


Hi.

I have put an AC-coupling cap on the FM linear input of
the Arturia miniBrute 2/2s main oscillator because most
modulation sources comes with DC offsets of more than
50mV (output opamps) and the note perceived pitch is
then shifted.

If the input is scaled, you not only change the FM mod.
amount but also the root pitch and I find this not acceptable.

Frédéric

Le 04/02/2020 à 11:43, mark verbos a écrit :
> It does if the modulator waveshape is asymmetrical. AC coupling 
> doesn’t really agree with our perception.
>
>
> Mark
>
>
>
>
>> On Feb 4, 2020, at 11:32 AM, Mattias Rickardsson <mr at analogue.org 
>> <mailto:mr at analogue.org>> wrote:
>>
>> Den mån 3 feb. 2020 01:30 <mskala at ansuz.sooke.bc.ca 
>> <mailto:mskala at ansuz.sooke.bc.ca>> skrev:
>>
>>     People think that linear FM doesn't
>>     shift the perceived pitch, and in order to help with that, it's
>>     common to
>>     make the input AC coupled.
>>
>>
>> Intriguing formulation there - do you mean it actually shifts the 
>> perceived pitch? :-)
>>
>> /mr - I think it can, amplitude does
>>
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