More non-linear sliders that I'd like to set to definitive values

Renoise Tool Development
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I figured out that time-based parameters on AHDSR are set to 60x^3, where x in [0,1] is the slider amount. Extrapolating from that, it looks like LFO’s Delay parameter is 8x^3 and Fader’s Duration and Delay parameters are 32x^3. So that leaves me with a few things:

  • What are the units for filter frequency and resonance? If I have a specific target frequency in Hz and resonance lift in dB, what 0-1 settings should I set in a modulation device? What about Drive?
  • What is the relationship between the LFO frequency slider and Hz/wavelength? It’s a bit confusing because it doesn’t appear to be exponential or power-based, I can’t quite get the curves to fit the data I see.

Thank you for your help!

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Let this maybe also serve as a feature request for a triangular LFO, which is what the SoundFont spec calls for - right now I’m akwardly combining a square and saw LFO to achieve the effect, which requires the square LFO to be exactly half the frequency of the saw. Which… requires the ability to set fairly exact frequency values.

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well, what about the custom waveform - and draw triangle to that and modify the speed?

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That would be very workable for the effects chain LFO, but unfortunately the modulation LFO (for e.g. pitch) doesn’t have custom shapes - it only supports sine, pulse, saw, and noise. It is possible to use a keytracker to get some of this, but that approach breaks with any polyphony.

5

Hey there!

What are the units for filter frequency and resonance? If I have a specific target frequency in Hz and resonance lift in dB, what 0-1 settings should I set in a modulation device? What about Drive?

I found the modulation filters follow the same curve as the native track-fx “Digital Filter” device. There is a Formula Device preset called “Keytracker Cutoff”, it will actually map digital filter to a keytracker. Also there this older work from me: [Effect Presets] tuned keytracked effects formulas/doofers Ktrk 1.1 - with more presets for other devices, but not modulation.

You can actually use the formula device to control a modulation macro and keytrack tune the instrument filter with the “Digital Filter” preset. I tried, it works, tuned bassdrum through high resonance with some drive - instant subbass.

As for the resonance and drive I can only say it’s different between the filters, it depends on their algorithm. For example the K35 Filter needs stronger push in resonance, while the Moog Filter rings much more easily, and the Diode Filter is somewhere in between and has a nonlinear reso range. The drive probably just boosts the signal, and sounds pretty similar between the effects, but I’ve not yet measured anything with that, it’s enough for me to tune the filters to a specific frequency. I.e. you can use the formula device to write a frequency to the filter (i.e. use a formula like y = frq2flt(440.0) to tune your filter to that frequency…

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What is the relationship between the LFO frequency slider and Hz/wavelength? It’s a bit confusing because it doesn’t appear to be exponential or power-based, I can’t quite get the curves to fit the data I see.

Just tested, it also follows a specific generic logarithmic curve, which you can see in the “Keytracker Cutoff” Formula Device preset.

Here I’ve applied the min/max parameters of the modulation LFO, and it gives perfect results (plug in from formula to mod set):

-- filter cutoff range --
local CUTOFF_MIN = 0.00195
local CUTOFF_MAX = 20
local CUTOFF_SCALING = 100.0

-- log scaling for the filter frequency as applied in Renoise
local function cutoff_lin2log(value)
  if value > 0.0 then
    return log10((CUTOFF_SCALING - 1.0) * 
      (value) + 1.0) / log10(CUTOFF_SCALING)
  else
    return 0
  end
end

-- maps hz value to a cutoff frequency parameter value
function frq2flt(frequency)
  local normalized = (frequency - CUTOFF_MIN) / (CUTOFF_MAX - CUTOFF_MIN)
  normalized = max(0, min(1, normalized))
  local scaled = cutoff_lin2log(normalized)
 return scaled
end

And the Formula: y = frq2flt(14.4) for a 14.4 Hz modulation LFO!

1 Like
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Thank you so much, this is perfect! My initial guess was to do a logarithmic lerp between the min and max values, but I think I was missing the -1 / +1 bits in your cutoff_lin2log function, so I was very slightly off. Glad to hear this works for filter frequency as well!

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The code is from Taktik… Sorry and I mixed something up…it’s not the digital filter device preset suitable for controlling the instrument filters, but the analog filter device. You can then set CUTOFF_MIN to 40 and CUTOFF_MAX to 18000 to get a correct keytracker mapping! CUTOFF_SCALING is also 100 I believe.

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One more question here if you’ll indulge me - is the frequency of the cutoff modulation (not the cutoff effect) automatically keytracked? It seems to be, but I can’t quite be sure.

edit - also, what units would Resonance (again on the sample modulation filter) be in?

10

One more question here if you’ll indulge me - is the frequency of the cutoff modulation (not the cutoff effect) automatically keytracked? It seems to be, but I can’t quite be sure.

No there’s no automatic key tracking, only the modulation device which will track according to the log/log curve - you need a formula for clean tracking

edit - also, what units would Resonance (again on the sample modulation filter) be in?

Oh idk it is often named “quality factor” or “Q”, and is given in percent or as a scalar. I don’t think there are any greater conventions, then again I am not an engineer and you maybe still want to look that up

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