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Modulate Frequency on ring modulator

Discussion in 'Building With Reaktor' started by BearClaw11, Mar 25, 2020.

  1. BearClaw11

    BearClaw11 NI Product Owner

    Messages:
    4
    Hi everyone,
    I would really appreciate it if someone could point me in the right direction, please.
    I have been trying to create a ring modulator to modulate incoming audio with a selectable oscillator. Everything has worked fine so far but I have hit a brick wall when trying to add an LFO to modulate the frequency of the oscillators. I have added an image of where I am now to help.
    Sorry if it is not correct I am very new to Reaktor.

    Many Thanks
    Wayne
     

    Attached Files:

  2. colB

    colB NI Product Owner

    Messages:
    3,228
    yes, this can be a sticky one.

    The lfo will give you an output ranging from -1 to 1.
    However, the frequency of the oscillator doubles at each octave, so you can't just multiply your lfo output by some constant (say 10) then add it to the frequency, that might work nicely at one pitch, but not at another.
    So either you use the pitch input of the oscillators, then scale the lfo output and add it to the pitch... or do some conversion.
    In core there is a really useful macro called DP2FF (delta pitch to frequency factor), this converts a difference in pitch into a value you can multiply a frequency by to get the required change. So e.g. if the input is -12, the output will be 0.5, multiply the frequency by 0.5 and it's the same as an octave down or -12 semitones - magic :)
    There is no primary equivalent to this, but it's easy to wrap it in a core cell:
    dp2ff.PNG
    you can then multiply the output of the LFO by whatever you want to get the maximum modulation you need:
    12 if it's +/- an octave, 2 if it's +/- a full tone
    then send the result to the dp2ff, then multiply your frequency value by the output of the dp2ff and send the result to the oscillators F input.
     
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  3. BearClaw11

    BearClaw11 NI Product Owner

    Messages:
    4
    First off sorry for taking so long to reply (I have been layed up with the virus) and secondly thank you very much for your help it worked perfectly.
    I do have one other stumbling block now though if you have any thoughts?
    I have been trying to add a depth knob to the ring mod and did so using the A inputs on the oscillators however it does not work as I thought and instead seems to alter the amplitude of the incoming audio? This time I have attached the instrument file as it is currently. Any suggestions or corrections would be greatly appreciated as I am really enjoying learning Reaktor.

    Thanks again for your help
    Wayne
     

    Attached Files:

  4. colB

    colB NI Product Owner

    Messages:
    3,228
    maybe add 1 to the modulator?

    If you multiply your signal with 0, then there will be no sound.... but if you multiply it by 1 there is no change... right?

    If you directly apply a bi-polar modulation signal with low amplitude using multiplication, it is near to zero so the result will be a low output level... but if you add 1 to your low level modulation signal, then the result varies by a small amount near to 1... so as you reduce the amplitude of the modulator you get closer to the original input level instead of closer to zero.

    EDIT:
    I'm not sure that there is a 'right way' here, it really depends on the context - you just have to try things out and think about what you're doing to the signal.
    e.g. if you add 1 to the modulator then, as the amplitude of the modulator rises from 0 to 1, you will get increased effect from your AM effect - but this is the type of effect that you would get from trying to use a vca for amplitude modulation - a 'two quadrant multiplier'. But if the modulations amplitude exceeds +/- 1, then there will be additional frequencies introduced as the signal is inverted by modulation levels less than -1.

    So maybe a better option for a ring modulator FX would be to just multiply the input with the modulator without an offset of 1 or an amplitude, and change the level of the effect by mixing the result with the dry input.
     
    Last edited: Mar 28, 2020
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  5. BearClaw11

    BearClaw11 NI Product Owner

    Messages:
    4
     
  6. BearClaw11

    BearClaw11 NI Product Owner

    Messages:
    4
    Great I think I understand now thank you. I replaced the Amplitude with a crossover to mix the dry and wet signals and used that as depth. Then I found giving the amplitude inputs of the oscillators a constant of 0.25 kept the input and output volume pretty much level.
     
  7. colB

    colB NI Product Owner

    Messages:
    3,228
    If it sounds right then it is right!
     
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