Juno6 emulation

#1

Hi all,

I try to build a Juno6 virtual synth. I have a draft version but it sound not like the analog version (comparison from sample on the Internet). I suspect my vcf implementation :

  • Juno 6 vcf have a 4Hz to 40KHz input range : how to do this with vcf axoloti object ?
  • Juno 6 vcf envelope modulation have a range of 10 octaves max : how to adapt adsr output for axoloti vcf pitch input ?
  • Juno 6 vcf is a 4 pole low pass filter : I read that it was possible to make a 24db/octave filter chaining to 2 pole low pass filter. Is it true ? Is it not a naïve approach ? I read on puredata forum it was preferable to use moog~ filter in order to emulate an analog 4 pole filter. This response from @johannes seems to say that the answer is not so simple.
  • Problem found by @DrJustice in the topic, can it have an impact on my juno vcf analog virtualization ?

Thanks for yours answers.

#2

Hi,

Chaining 2 12dB/oct filters will indeed give a 24dB/oct roll-off, but it will not have the same as the classical 4-pole VCF. If you use 2 two-pole filters, it's better to tune the two filters a bit apart to reduce harsh resonance peaking.

Envelope modulation over 10 octaves, I think that is too wild to behave. Maybe with all modulation sources to the filter frequency combined: keytracking, lfo, envelope, slider, pitch/modulation stick.

I published a draft 4-pole filter in axoloti-contrib/patches/jt/devel/...cfr here

#3

Thanks for your answer. I am currently testing the 4-pole filter.
Concerning envelope modulation I don't understand why Juno 6 specifications talk about envelope modulation over 10 octaves. In the same manual, lfo modulation is over 8 octaves and keytracking seems to modulate all the vcf frequency range (4Hz to 40kHz)...

#4

You can use "conv/unipolar2bipolar" to stretch the envelope output to a 128 units (semitones on a pitch inlet), that covers 10.6 octaves.

#5

Ok, I had not seen this solution :slight_smile:

For vcf frequency range (4Hz..40kHz), I don't understand why Juno6 synth have a wide input frequency range. Is there a reason ? Maybe all high frequencies, when combined, can be heard.
But, if I'm not mistaken, with 48kHz for s-rate, it does not make sense to set a vcf with a frequency input to 40kHz.

Sorry for all this noob questions. :slight_smile:

#6

The highest frequency that can actually exist at 48kHz sample rate is 24kHz, anything higher than that just aliases (that is to say it sort of reflects back down and becomes a different frequency - usually one you don't want). So 24kHz would be the theoretical maximum for filters on the Axoloti and you're right, 40kHz wouldn't make sense (or even be possible). Not sure why the axo filters are limited to 12kHz though. Perhaps it's more efficient?