[sdiy] Ring Mod (was Re: Hadamard Transform Network)
Magnus Danielson
magnus at rubidium.dyndns.org
Fri May 19 12:43:11 CEST 2017
Hi,
A "ring modulator" derives its name from the diode ring of a
double-balanced mixer (which also uses two transformers). Such mixers is
still used in RF, but less so in audio context. The 4-quadrant
multiplier of the Gilbert cell allowed normal analog semiconductor use.
"ring mod" is a 4-quadrant multiplier, but a Gilbert cell is another
4-quadrant multiplier. Thus, two quite distinct implementation forms of
a 4-quadrant multiplier has distinct and separate names.
The synthesizer user "ring mod" function can thus have distinct
different implementations.
Then we have "cheap" "ring-modish" types where one or both waveforms is
square-wave or PCM. This is not what I expect from a full "ring mod".
Cheers,
Magnus
On 05/17/2017 02:38 AM, David G Dixon wrote:
> 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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