[sdiy] frequency shifter
admin at bugbrand.co.uk
Wed Mar 11 20:49:22 CET 2020
Don't feel you *have* to get tangled up in maths - I could do maths up
through my technical university course, but frankly it never conveyed
spirit to me & I rarely go anywhere deep with it in any of my designing.
I was also going to suggest looking up the CGS Dome Filter (the phase
shift network mentioned) but don't think schematics were presented - it
does, however, state the Electronotes article I referred to - #83
On 11/03/2020 15:22, ColinMuirDorward wrote:
> I'm still working on these replies, folks, thanks for the discussion!
> OK, TBH, I'm pretty lost. It's probably beyond me without having the
> math. Is it anything like barber-poling a series of APF filters?
> On Wed, Mar 11, 2020 at 9:43 AM Quincas Moreira <quincas at gmail.com
> <mailto:quincas at gmail.com>> wrote:
> This is a celebrated one, by JHaible. I have the pcb, waiting for
> the day when i’ll have time to source the parts...
> Sent from my iPhone
>> On 11 Mar 2020, at 4:11, Tom Bugs <admin at bugbrand.co.uk
>> <mailto:admin at bugbrand.co.uk>> wrote:
>> My brain is not awake enough to closely follow Dave's
>> description! But I remember there's a good basis in an old
>> Electronotes - I didn't follow it exactly by any stretch but it
>> really helped me design my own, the theory I took being:
>> 1) make a quadrature sine/cosine VCO
>> 2) audio input splits to two 6-stage all-pass filter
>> 3) each filter-chain is followed by a RingMod/Multiplier with the
>> modulating input coming one from sine / one from cosine
>> 4) then you do sum & difference of the two ring mods to get up &
>> down shifts.
>> What I really enjoyed was adding feedback! In fact, redeveloping
>> the ideas at the moment & adding in a bit of extra control +
>> output mixing/panning. Really great audio processor, even at LFO
>> rates where it becomes a wonderful phaser type machine.
>> On 11/03/2020 07:28, David G Dixon wrote:
>>> I built a frequency shifter following the Bode plan. This is
>>> frequency shifting by manifesting certain trigonometric
>>> product-to-sum formulae using electronic circuits:
>>> sin u sin v = 0.5 [cos(u – v) – cos (u + v)]
>>> cos u cos v = 0.5 [cos(u – v) + cos (u + v)]
>>> So, if you have two signals with their 90-degree quadrature
>>> signals (say, u is the audio you want to shift and v is the
>>> on-board quadrature oscillator), then if you multiply the
>>> signals together (using a four-quadrant multiplier) and also
>>> multiply their quadrature signals together (using a second
>>> four-quadrant multiplier) then you can sum the multiplier
>>> outputs together, and you will get the following (by adding the
>>> two equations together):
>>> cos (u – v)
>>> This represents the audio signal u which has been
>>> frequency-shifted downward by the frequency of the oscillator
>>> signal v. Of course, the audio signal probably has many
>>> frequencies u occurring simultaneously, and they will all be
>>> shifted down by v. That’s what makes frequency shifting sound so
>>> alien and weird.
>>> By being clever with the summations of the multiplier output
>>> signals (based on a little bit of algebra), you can also recover
>>> the up-shifted audio:
>>> cos (u + v)
>>> With both the down- and up-shifted signals, you can get a stereo
>>> The entire circuit consists of a 90-degree phase displacement
>>> network to generate the cosine of the incoming audio (I designed
>>> mine with 12 stages from 15 Hz to 15 kHz using a little thing I
>>> found on the internet called QuadNet), a quadrature oscillator
>>> to generate both sine and cosine waves at frequency v (mine is
>>> TZFM and consists of two Rubicon cores with sine shapers, with
>>> one syncing the other in such a way that the two are always 90
>>> degrees out of phase), two four-quadrant multipliers (I built a
>>> dual unit from a single 2164 chip – two linearized VCAs), and a
>>> couple of output amplifier stages for doing the summing. The
>>> key to success is to AC couple the signals into the multipliers
>>> to eliminate DC offsets in the incoming signal, which is the
>>> single largest source of error in the circuit. If that is done
>>> properly, the multipliers require no trimming (if accurate
>>> summing resistors are chosen).
>>> The circuit works great and sounds super freaky. I’m going to
>>> be building another one for one of our members here shortly.
>>> *From:*Synth-diy [mailto:synth-diy-bounces at synth-diy.org] *On
>>> Behalf Of *ColinMuirDorward
>>> *Sent:* Tuesday, March 10, 2020 7:01 PM
>>> *To:* *SYNTH DIY
>>> *Subject:* [sdiy] frequency shifter
>>> Hi, I got a little lost trying to understand what a frequency
>>> shifter is. I mean the pre-digital method used by Moog (I think?).
>>> I recently built a 4pole APF, and was really impressed with some
>>> of the pitching effects I could achieve with it. I'm guessing
>>> this is an entirely different method than the frequency shifters
>>> like Moog and JH have done.
>>> Is the APF method used by anyone? What are its limitations, and
>>> what is it even doing?
>>> Well, I guess I'm just looking for some conversation on the
>>> topic of analog frequency/pitch shifting methods. If anyone has
>>> any thoughts/experience they'd like to share.
>>> Synth-diy mailing list
>>> Synth-diy at synth-diy.org <mailto:Synth-diy at synth-diy.org>
>> BugBrand LTD
>> UK company No. 07199808
>> VAT No. GB 988 2629 57
>> 1 Ninetree Hill
>> BRISTOL BS1 3SB
>> United Kingdom
>> www.bugbrand.co.uk <http://www.bugbrand.co.uk>
>> Virus-free. www.avg.com
>> Synth-diy mailing list
>> Synth-diy at synth-diy.org <mailto:Synth-diy at synth-diy.org>
> Synth-diy mailing list
> Synth-diy at synth-diy.org <mailto:Synth-diy at synth-diy.org>
UK company No. 07199808
VAT No. GB 988 2629 57
1 Ninetree Hill
BRISTOL BS1 3SB
This email has been checked for viruses by AVG.
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the Synth-diy