[sdiy] Ring Mod (was Re: Hadamard Transform Network)
Tony K
weplar at gmail.com
Wed May 17 03:17:24 CEST 2017
err that's "double sideband" rather.
> On May 16, 2017, at 9:16 PM, Tony K <weplar at gmail.com> wrote:
>
> Hi Magnus, your radio example reminded me of how a synchronous detector works , by picking out one of the sidebands of an AM , or double-sided , signal and phase locking it to a local carrier to reduce distrortion. I never thought of this as "ring modulation" or how this could be applied to audio. Interesting.
>
> I have discovered some things purely by accident, like riding the BFO or VFO at the low end of the frequency synthesizer , to generate nice "radio" sines waves. One can CV this process too, with a varactor diode in the 1 Mhz VFO. But this probably has nothing to do with ring modulation. So I will shut up now.
>
> 73's
>
>> On May 16, 2017, at 7:43 PM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
>>
>> 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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