Playing the filter frequency of Synapse AF-4 with CV

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diminished
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Post 03 Aug 2019

I have plenty of CV tools at my disposal, but I'm a complete CV noob. Can you help, please?

I would like to send "tuned" CV to the CV-in of AF-4's filter while it's self-resonating.
In my case it's E minor. I know the corresponding frequeny values of the scale. But other than that, I'm lost.

What tool should I use to send discrete and only discrete CV values to AF-4?
How would I sequence those signals?
Can I use MIDI for said sequencing?
Is the "resolution" of CV enough to cover roughly two octaves?

Thanks in advance!

Edit: and is the only way to find out the corresponding CV value of a frequency by trial and error?

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diminished
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Post 03 Aug 2019

Oh and how much more CV is an octave up: two times? Octave down = 0.5*CV_value?

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Loque
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Post 03 Aug 2019

AFAIR the Synapse filter has a note input. Add a RPG8 to the rack without any connections. Connect the Note Out from RPG8 to the filter Note In.

If the filter does not have a Note input, things getting complicated...

Mind, that RPG8 and CV is monophonic.

In the internet you can find plenty note/frequency mapping tables...
:reason: 10, Win10 64Bit.

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selig
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Post 03 Aug 2019

Interesting question, not sure there's an easy answer. While there IS a pitch CV standard in Reason, there isn't a frequency standard. So I would guess in most cases the CV input for a filter control would cover the range of the knob (sometimes more). Since the range of the filter knob can vary from device to device, it probably will be trial and error. Best way imo is to send alternating notes an octave apart and adjust the CV trim until you hear octaves on the filter. Tip: send a synth through the filter playing the same notes so it will be obvious when you are spot on pitch.

After much frustration with existing Reason filter and EQ devices not being able to be tuned to semitones, I created one myself (ColoringEQ). The goal was to be able to "play" the filter/eq, or to track MIDI notes for technical (EQ ducking based on the note played) and creative (turning drums into melodies or bass lines) uses. Sounds like you're after something similar here too?

I would be happy to find the trim value, but I don't have that device (one of the few Synapse devices I do not have).
Selig Audio, LLC

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selig
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Post 03 Aug 2019

Loque wrote:
03 Aug 2019
AFAIR the Synapse filter has a note input. Add a RPG8 to the rack without any connections. Connect the Note Out from RPG8 to the filter Note In.

If the filter does not have a Note input, things getting complicated...

Mind, that RPG8 and CV is monophonic.

In the internet you can find plenty note/frequency mapping tables...
https://www.propellerheads.com/shop/rac ... og-filter/
Cutoff CV only, no "note cv".
Should only require trimming the CV value to produce the proper scale, then offsetting (via front panel) to line the scale up with A-440.

[note: I have GQ7 and checked to see how close it was to responding to CV Note. It's close, but a little too narrow between octaves. That means it needed to be scaled up, which most CV tools should do (I got a value of around 1.07x).
BTW, the way to test this is to run a synth sine wave through the filter, then tune lower octave for highest peak value (this indicates you are tuned the closet to the desired pitch). Then play an octave up and see how close to the same peak value. If not as high, you'll need to adjust scale until you see the highest peak value. Sadly, scaling will also affect the lower octave, so you'll have to repeat a few times. Maybe even better to compare 3-4 octaves apart, as it will show a bigger difference and be easier to tune - you can then assume all octaves in between will be in tune, and thus also all semitones across that range.]
Selig Audio, LLC

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Loque
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Post 03 Aug 2019

selig wrote:
03 Aug 2019
Loque wrote:
03 Aug 2019
AFAIR the Synapse filter has a note input. Add a RPG8 to the rack without any connections. Connect the Note Out from RPG8 to the filter Note In.

If the filter does not have a Note input, things getting complicated...

Mind, that RPG8 and CV is monophonic.

In the internet you can find plenty note/frequency mapping tables...
https://www.propellerheads.com/shop/rac ... og-filter/
Cutoff CV only, no "note cv".
Should only require trimming the CV value to produce the proper scale, then offsetting (via front panel) to line the scale up with A-440.
Ok. There just a few filters with Note In 🤨
Are the notes spread linear?
:reason: 10, Win10 64Bit.

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diminished
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Post 03 Aug 2019

Quick question(s): how would I trim? Is trimming something like matching the resolution of the output and the input? What tool would you use? I have all the Pandas at my disposal fwiw. And.. how do I space my CV values in regards to a minor scale? Will the _relative_ spacing be the same for any minor scale?

Coloring EQ is on my wishlist, but the last Rig upgrade deal didn't convince me. That's not ColoringEQ's fault though:)

@Loque: here's the spacing / Hz values:
http://pages.mtu.edu/~suits/notefreqs.html

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diminished
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Post 03 Aug 2019

selig wrote:
03 Aug 2019
Sounds like you're after something similar here too?
Before I wrap my mind around everything said, I'd like to answer the question because I imagine my goal to be something nice, unique and beautiful. I'd like to occasionally intruduce ratchet style apreggios and glissandos into drumloops, then revert to the root note, turning it off again. Drive the filter here and there. AP-4 sounds beautiful in my opinion when self-oscillating and it's very stable. The transition between self-oscillation and normal filter behavior is supposed to be the playground :) I hope this makes sense.

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selig
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Post 03 Aug 2019

diminished wrote:
03 Aug 2019
Quick question(s): how would I trim? Is trimming something like matching the resolution of the output and the input? What tool would you use? I have all the Pandas at my disposal fwiw. And.. how do I space my CV values in regards to a minor scale? Will the _relative_ spacing be the same for any minor scale?

Coloring EQ is on my wishlist, but the last Rig upgrade deal didn't convince me. That's not ColoringEQ's fault though:)

@Loque: here's the spacing / Hz values:
http://pages.mtu.edu/~suits/notefreqs.html
Basically you first need to get the filter to "track" the keyboard chromatically (semitones), then you can use a Player to restrict notes to a scale if necessary.
Selig Audio, LLC

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Loque
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Post 03 Aug 2019

selig wrote:
03 Aug 2019
diminished wrote:
03 Aug 2019
Quick question(s): how would I trim? Is trimming something like matching the resolution of the output and the input? What tool would you use? I have all the Pandas at my disposal fwiw. And.. how do I space my CV values in regards to a minor scale? Will the _relative_ spacing be the same for any minor scale?

Coloring EQ is on my wishlist, but the last Rig upgrade deal didn't convince me. That's not ColoringEQ's fault though:)

@Loque: here's the spacing / Hz values:
http://pages.mtu.edu/~suits/notefreqs.html
Basically you first need to get the filter to "track" the keyboard chromatically (semitones), then you can use a Player to restrict notes to a scale if necessary.
I tried it a few times to "play" a filter without a note input. I had no success with the tracking of the note to frequency. Any detailed info or an example is appreciated.
:reason: 10, Win10 64Bit.

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selig
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Post 03 Aug 2019

Loque wrote:
03 Aug 2019
selig wrote:
03 Aug 2019


Basically you first need to get the filter to "track" the keyboard chromatically (semitones), then you can use a Player to restrict notes to a scale if necessary.
I tried it a few times to "play" a filter without a note input. I had no success with the tracking of the note to frequency. Any detailed info or an example is appreciated.
It can be confusing because we are adjusting two aspects of the Note CV, which is already quantized to semitones.

One aspect is the scaling: toe goal is for each semitone of change on the incoming CV to result in a semitone of change on the filter. This effect is the same thing as adjusting Keyboard Tracking on a filter (or oscillator). You are expanding or contracting the 127 notes against a fixed range of frequencies - only when key track is 100% to you get exactly 12 steps per octave. The problem here is you don't know exactly where this "100%" falls…

The second aspect is the offset - once you get the tracking correct, a "C" on the input may not equal a "C" on the filter. This is basically a "transpose" related issue, and the quickest way to fix it is to adjust the filter frequency so that the note you play is the note you hear. Make sense?

OK, so the problem with the scaling stage is that when you scale, you affect every non-zero value. So if you compared C2 to C4, you can get C2 in tune and then when you adjust scaling to get C4 also in tune, you affect C2 as well. So you go around in circles until you're close enough to not hear any tuning issues. I usually play a repeating sequence of 2-4 octaves every 1/4 note when working on this process, with a steady reference tone playing in the background for the lowest octave.
Selig Audio, LLC

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diminished
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Post 03 Aug 2019

Yay, I made progress!

It was a PITA to dial in on CV janitor, but I managed to play one octave in C Major!
Is there any way to get even finer CV multiplier values than the knobs allow?

Here's the Reason file if anyone's interested and would like to expand on that. I will definitely try and then find a way to trigger via midi. The only non-free RE needed is - obviously - Synapse AF-4.
playingthefilter01.zip
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Loque
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Post 03 Aug 2019

diminished wrote:
03 Aug 2019
Yay, I made progress!

It was a PITA to dial in on CV janitor, but I managed to play one octave in C Major!
Is there any way to get even finer CV multiplier values than the knobs allow?

Here's the Reason file if anyone's interested and would like to expand on that. I will definitely try and then find a way to trigger via midi. The only non-free RE needed is - obviously - Synapse AF-4.

playingthefilter01.zip
Yea, you can scale it again with Janitor.
:reason: 10, Win10 64Bit.

User avatar
diminished
Posts: 943
Joined: 15 Dec 2018

Post 03 Aug 2019

Loque wrote:
03 Aug 2019
diminished wrote:
03 Aug 2019
Yay, I made progress!

It was a PITA to dial in on CV janitor, but I managed to play one octave in C Major!
Is there any way to get even finer CV multiplier values than the knobs allow?

Here's the Reason file if anyone's interested and would like to expand on that. I will definitely try and then find a way to trigger via midi. The only non-free RE needed is - obviously - Synapse AF-4.

playingthefilter01.zip
Yea, you can scale it again with Janitor.
:lightbulb:

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Loque
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Joined: 28 Dec 2015

Post 03 Aug 2019

I stick with my first post...if the filter does not have a note input, things get complicated. Its much easier with F-16, even if it cannot be played directly.
:reason: 10, Win10 64Bit.

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