lfo documentation
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website/src/pages/learn/lfo.mdx
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website/src/pages/learn/lfo.mdx
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---
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title: Low-frequency oscillators (LFO)
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layout: ../../layouts/MainLayout.astro
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---
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import { MiniRepl } from '../../docs/MiniRepl';
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import { JsDoc } from '../../docs/JsDoc';
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# Low frequency oscillators (LFO)
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A low frequency oscillator (or short LFO) is a common way on synthesizers to continuously modulate various signals.
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This documentation is an interactive version of glossing's tutorial https://www.youtube.com/watch?v=11frBA9L638
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## Applying an LFO
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Here, the LFO will change the frequency of the `saw`. Put a comment like this `//.lfo()` to see and hear how it changes, and remove the comment again.
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<MiniRepl
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client:idle
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tune={`
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s("saw").lfo()
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.lpf(800)
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._spectrum({height: 300, width: 800})`}
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/>
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By default, the LFO will modulate the control parameter which is right before `.lfo()`:
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<MiniRepl
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client:idle
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tune={`
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s("saw")
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.lpf(800).lfo()
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._spectrum({height: 300, width: 800})`}
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/>
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Here, the LFO will modulate the low pass filter `.lpf`.
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## Moving away from the default
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The following sections explain how pass parameters to `.lfo`. Similar to `._spectrum` above, almost all the configuration of `lfo` lives inside a json object, starting with `{` and ending with `}`.
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All the parameters (except `id`) are written as `key: value` inside and separated by `,`.
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The reference refers to them as `config.key`, i.e. for the following one as `config.control` but you use them like below.
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## Control
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`control` determines which parameter will be modulated. This allows you to place your `lfo` at different places,
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not necessarily immediately after the controlled parameter.
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Here, we place `lfo` after the `s`, but it modulates the low pass filter.
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<MiniRepl
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client:idle
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tune={`
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s("saw")
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.lfo({control:'lpf'})
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.lpf(800)
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._spectrum({height: 300, width: 800})`}
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/>
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You can even influence parameters which are always present, even if you haven't explicitly written them, like `gain`.
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<MiniRepl
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client:idle
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tune={`
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s("saw")
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.lfo({control:'gain'})
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.lpf(800)
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._spectrum({height: 300, width: 800})`}
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/>
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`control` has an alias `c`.
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## Rate
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`rate` determines how often the `lfo` oscillates per second:
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<MiniRepl
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client:idle
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tune={`
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s("saw")
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.lfo({c:'gain', rate:"<2 4>"})
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.lpf(800)
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._spectrum({height: 300, width: 800})`}
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/>
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The alias of `rate` is `r`.{' '}
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## Sync
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Instead of controlling the frequency with `rate` by setting a frequency in Hz, you can use `sync`
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to snychronize your lfo with your other patterns.
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`sync` expresses this frequency as "times per cycle"
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Try removing the `sync: "<2 4 8 0.5 >"` from the pattern and notice that there is something not in sync.
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<MiniRepl
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client:idle
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tune={`
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$: s("bd*4").bank("TR909").postgain(0.5)
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$: s("saw")
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.lpf(800)
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.lfo({sync: "<2 4 8 0.5 >"})
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._spectrum({height: 300, width: 800})`}
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/>
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You can put patterns into the parameters of `lfo` if you want them to change over time, as seen above.
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## Relative Depth
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`.depth` is relative depth, a value of 1 (the default) means that
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the value goes above and below by half of the value which is being modulated
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E.g. for depth `1`, it modulates the frequency to oscillate between 32 = (64/2) and 96 (= 64 + 64/2).
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<MiniRepl
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client:idle
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tune={`
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s("saw").freq(64)
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.lfo({r: 2, depth: "<1 2 3>"})
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.lpf(800)
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._spectrum({height: 300, width: 800})`}
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/>
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The `freq` is not needed here, as this is the default frequency, it's just for instructive purposes.
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The aliases of `depth` are `dr` and `dep`.
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## Absolute Depth
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`depthabs` controls the absolute modulation depth. For example you can modulate
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the low pass filter by exactly 250 Hz up and below:
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<MiniRepl
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client:idle
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tune={`
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s("saw")
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.lpf(800)
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.lfo({r: 2, depthabs: "250"})`}
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/>
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The alias of `depthabs` is `da`.
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## DC offset
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If you don't want to go up or down by the same amount with your modulation, then you can shift the center of the modulation with `dcoffset`.
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The default value is -0.5, which is the middle point between:
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"dcoffset = 0: All modulations increase the control parameter (or keep it constant)"
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"dcoffset = -1: All modulations decrease the control parameter (or keep it constant)"
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Other values will work as well.
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<MiniRepl
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client:idle
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tune={`
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s("saw")
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.lpf(600)
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.lfo({r: 2, da: "200", dcoffset: "<-0.5 -1 -0.5 0>"})`}
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/>
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The marvellous alias of `dcoffset` is `dc`.
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## Shape
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You can change the shape of the modulation with `shape`. The default is `triangle`, but other shapes are available too:
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<MiniRepl
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client:idle
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tune={`
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s("saw")
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.lpf(800)
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.lfo({r: 2, shape: "<triangle sine ramp saw square>"}) `}
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/>
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You can add `._spectrum()` to see the shape of the modulations in the spectrum.
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You can also get these shapes by using numbers:
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| Shape | number |
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| -------- | ------ |
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| triangle | 0 |
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| sine | 1 |
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| ramp | 2 |
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| saw | 3 |
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| square | 4 |
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this way, you can use a function like `irand` to generate numbers:
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<MiniRepl
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client:idle
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tune={`
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s("saw")
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.lpf(800)
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.lfo({r: 2, shape: irand(4)}) `}
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/>
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The alias of `shape` is `sh`.
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## Skewing some shapes
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You can influence some of the shapes (`triangle` and `square`) in more detail.
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The default skew is 0.5, it does different things for these two.
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For `triangle`, it skews the top of the triangle to the left or right,
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where 0 makes it look like `saw` and 1 makes it look like `ramp`.
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For `square`, the skew influences the pulse width (see reference for `pulse` and `.pw`):
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<MiniRepl
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client:idle
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tune={`
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s("saw")
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.lpf(800)
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.lfo({r: 2, sh: "<triangle square>/5",
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skew: "<0 0.25 0.5 0.75 1>"}) `}
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/>
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The alias of `skew` is `sk`.{' '}
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## Curve
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You can change the curves of your lfo and can make it more intense.
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The default value is 1. Writing numbers greater than one can make it more intense,
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numbers between 0 and 1 will make it less intense.
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This will raise the lfo to the power of curve, so larger numbers (such as 10) can have very unexpected results.
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<MiniRepl
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client:idle
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tune={`
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s("saw")
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.lpf(800)
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.lfo({r: 2, sh: "<triangle>", curve: "<1.3 1 0.75 1>"}) `}
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/>
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## Referencing your lfos with id
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All the lfos are numbered from the first starting with 0, the second having an `id` of 1 and so on.
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You can refer to this in a later call if you want to modify a specific `lfo`.
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The ´id´ is outside of the config json (which is different from the other parameters of `lfo()`
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Try out how the sound changes when you replace the 0 with a 1.
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<MiniRepl
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client:idle
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tune={`
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s("saw").lfo().lpf(800)
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.lfo({s: "<4 8 0.5>"})
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.sometimes(x => x.lfo({dr: "4"},0))`}
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/>
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You can also name your lfos and refer to them by name, using the `id` parameter
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<MiniRepl
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client:idle
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tune={`
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s("saw").lfo({}, "lfo_freq_saw").lpf(800)
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.lfo({s: "<4 8 0.5>"}, "lfo_lpf")
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.sometimes(x => x.lfo({dr: "4"},"<lfo_lpf lfo_freq_saw>"))`}
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/>
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## FX index
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If you are using `FX()` to reorder your effects, you dont need to write your lfos inside the `FX`,
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but instead can refer to them by their FX index (starting with 0)
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<MiniRepl
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client:idle
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tune={`
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s("saw").FX(
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distort(3),
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gain(0.3), // this has the fx index 1
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lpf(400)
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).lfo({s: 16, dr:2, c:"gain", fxi: 1})`}
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/>
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## Modulating other LFOs with Sub-control
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LFOs can modulate other lfos and will modulate their frequency (given by `r` or `s`):
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<MiniRepl
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client:idle
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tune={`
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s("saw").lpf(400).gain(0.8)
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.lfo({s: 16, dr:2, c:"gain"})
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.lfo({s: 0.3, dc:-1, dr: 0.8})`}
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/>
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To modulate other parameters of the first lfo (like `skew`, `depth` and so on), we can specify this with `subControl`or
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its alias `sc`
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<MiniRepl
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client:idle
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tune={`
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s("saw").lpf(400).gain(0.8)
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.lfo({s: 4, dr:2, c:"gain"})
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.lfo({s: 0.3, sc: "skew"})`}
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/>
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