[sdiy] Ring Mod (was Re: Hadamard Transform Network)

[David G Dixon]

I just wanted to say here publicly that I tried to build a Weaver frequency
shifter from two 4-quadrant balanced modulators, two SV filters, and some
sinewave oscillators.  All the bits and pieces worked perfectly, and I
derived, rederived, checked and rechecked all the math and was absolutely
sure that everything was hooked up correctly.  It didn't work.  I gave up on
the whole idea.  I don't believe that a musical Weaver frequency shifter can
be built.

Also, if a "ring modulator" and a "4-quadrant balanced modulator" give
exactly the same transfer function, then why can't the terminology by used
interchangeably?


> -----Original Message-----
> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On 
> Behalf Of Magnus Danielson
> Sent: Tuesday, May 16, 2017 4:43 PM
> To: synth-diy at synth-diy.org
> Cc: magnus at rubidium.se
> Subject: Re: [sdiy] Ring Mod (was Re: Hadamard Transform Network)
> 
> Hi,
> 
> The frequency shifting is just a Single Side Band (SSB) modulator.
> 
> One version of frequency shifter popular in synthesizer world 
> uses two all-pass filters to create outputs with near 90 
> degrees phase-angle, i.e. I and Q output.
> 
> Once in a lab far far away, another approach was tried, in 
> which a poly-phase filter was created, which had interaction 
> between the 0, 90, 180 and 270 degree angles rather than 
> being independent filters. Such filter had been used within 
> radio-context.
> 
> Another approach to create SSB, which is known in ham radio 
> context, is to do normal AM, and then let a sharp filter, 
> i.e. a crystal filter, to remove one side-band and carrier. 
> For use in a audio frequency shifter context, you would mix 
> up with one frequency, remove the lower side-band, and then 
> mixdown with another frequency. The frequency difference 
> between the frequencies would introduce the frequency shift.
> The same frequency source could be used and then could the 
> second frequency be generated by mixing the up-shift 
> frequency with a shift oscillator frequency. Due handling of 
> mirror frequencies needs to be done. This is what we do with 
> two radios on regular basis as one is not in tune to another.
> 
> As for ring-mods, those refers to the ring-modulators that is 
> also called double-balanced mixers. Those by itself is not 
> necessarily square wave mixing, that is only one of many 
> operational modes. It is also not what I think about for 
> sounding best. I want sine as one signal for purest ring-mod sound.
> 
> Cheers,
> Magnus
> 
> On 05/16/2017 08:38 PM, Mattias Rickardsson wrote:
> > 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
> > <mailto: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 <mailto:mskala at ansuz.sooke.bc.ca>
> >            People before principles.
> >     http://ansuz.sooke.bc.ca/
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