[sdiy] Ring Mod (was Re: Hadamard Transform Network)
Mattias Rickardsson
mr at analogue.org
Tue May 16 20:38:01 CEST 2017
It seems like everyone suddenly trigged on this trig' question.
Trig-OhNo!-metry.
Apropos the sum & difference frequencies:
Frequency shifting can be done with two ringmods (that are fed with sine &
cosine, and adding clever all-pass filtering to phase shift them into
cancellation of unwanted parts), but this involves quite an advanced setup.
Are there any other useful but simpler tricks you could do with
combinations of ringmods?
/mr
Den 16 maj 2017 6:56 em skrev <mskala at ansuz.sooke.bc.ca>:
> On Tue, 16 May 2017, Tim Ressel wrote:
> > But you bring up an interesting point: 4QMs multiply, but they produce
> x+y,
> > x-y tones. Anyone got the math on that?
>
> It's a basic trig identity:
>
> (cos a)(cos b) = 1/2 [ cos (a+b) + cos (a-b) ]
>
> If a and b are two different multiples of t (time), then cos a and cos b
> are two sine waves of different frequencies, and then you end up with the
> sum and difference frequencies.
>
> One could prove this identity with the power series expansion for cos, if
> necessary.
>
> --
> Matthew Skala
> mskala at ansuz.sooke.bc.ca People before principles.
> http://ansuz.sooke.bc.ca/
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