Friday, 31 May 2019

Spectral chorus - another 'Hex' MaxForLive device

For a long time, I have been trying to find a good way to provide an intuitive user interface for 'Modulated Pan Position'. You can see me experiment with various ways to implement it in many of my MaxForLive devices - what I have always needed is a simple/obvious way of allowing control over pan position, but also allowing that pan position to be modulated by an LFO.

The 'traditional' way of doing this (and I have used it a lot: albeit unwillingly...) is to have a pan position (a slider is nice and intuitive) plus an LFO 'modulation depth' rotary control. That's two controls, and there is an implicit interaction between them where the LFO over-drives the panning so that the position goes to left or right and stays there, then suddenly pans across - it's because the LFO waveform (typically a sine wave) is over-driving the pan position, and the clipping of the waveform gives 'flat' spots in the auto-panning (Yuk!).

This is why, in AUDhexCHORUS, I'm introducing something that I have been working on for quite a while: a single UI widget that does pan position AND modulation depth combined together.

Here's the UI widget" The components are:

1. a 'thumb' (the bright white vertical bar) that you click with the mouse to control the setting of pan position and LFO modulation.
2. an LFO indicator (the big purple block) that shows the current pan position. (When the LFO modulation is active (as it is here) then this slides horizontally from left to right to show where the audio is in the stereo image.
3. two numbers that show the horizontal and vertical position of the 'thumb'. (These cn be used as mapping targets for other M4L devices)

The UI metaphor is very straight-forward: horizontal is pan position (Left is left, Right is right!), whilst up and down controls the depth of LFO modulation - and there's a triangle graphic that shows you where you need to position the 'thumb' to avoid over-modulation of the pan position. The 'thumb' that you click on is a vertical bright white bar, so when you move it horizontally it looks like a pan position slider, but when you move it upwards, then the LFO modulation is gradually increased, and if you move it all the way to the top of the triangle, then you get perfect side-to-side pan LFO modulation, with no 'hold' at either side. It makes using pan position/modulation SO much easier!

Here's a GIF that shows the UI widget in three modes.

The top example shows the 'thumb' in the 'sweet spot' position at the top of the triangle where the LOF modulation is maximised without clipping. Here the LFO modulation (the purple block) will move the pan position from hard Left to hard Right, without any major pausing at the Left or Right positions. If you move the 'thumb' to the left or the right away from the top of the triangle, then the LFO will spend time at that side (The waveform will be clipped), and may not go all the way across to the opposite direction. (The animated GIF has jerks in the way that the purple block moves - this is because of the looping in the GIF - in the actual device the purple block moves smoothly from sid to side, indicating the LFO-controlled pan position.)

The middle example shows the 'thumb' right in the centre, and so the pan position is only slightly modulated by the LFO.

The lower example shows the 'thumb' in the 'down' position, and this completely removes any LFO modulation, so horizontal movements of the 'thumb' just control the (fixed) pan position. The two numbers underneath the UI widget are the horizontal and vertical positions, and can be used as a target for mapping by LFOs and other M4L devices that use controller mapping. in this case, the 'thumb' is all the way to the left, and so the audio will be panned hard to the Left of the stereo image.


To accompany a neat pan UI widget, there's a neat device: AUDhexCHORUS (AhC for short, to save my fingers as I type!) There are lots of chorus devices out there, but this one has a few 'specials' that make it more interesting...

1. The 'Pan Position/Modulation Widget! (Of course!)

2. Spectral controls, as per some of the previous 'Hex' devices. You have three spectral 'bands' to play with, so you can have different chorus amounts/styles wherever you want across the frequency spectrum, and you can have different bands for the Left and Right stereo channels if you want.

3. Envelope tracking makes the chorus depth tracks the amplitude of the incoming signal... This is particularly good for dynamic sounds...

The actual chorus effect is achieved by using frequency shifting (Via ring modulation (which just multiplies two audio signals together) and can also be called a four-quadrant multiplier or a balanced modulator.) instead of using a modulated delay line. A future version might allow switching between the two methods - let me know if you would like this.

AUDhexCHORUS is a 'wide' device (It uses lots of screen 'real estate' in Ableton Live, so be prepared for some horizontal scrolling) - I'm not known for making 'one-rotary-control' devices!

In detail

AUDhexCHORUS is symmetrical, so both halves of the user interface are mirrored. Let's look at the left hand side - which covers the Left channel. Vertically, there are three similar rows of controls (one for each spectral band), and horizontally there are three similar processing blocks. Going across the blocks from left to right there are:

- The Frequency Shift block, which contains:
-- the frequency shift rotary controls,
-the envelope amount rotary controls (which increase the amount of frequency shift depending on the envelope of the incoming audio),
-- the vertical envelope depth indicator,
-- the smoothing rotary control (which smoothes the envelope control),
-- the 'sideband select' buttons (which select positive frequency shifts, negative or both),

- The Spectral Filter block, which contains:
-- the frequency rotary controls (high-pass in the upper row, band-pass in the centre row, and low-pass in the lower row),
-- the resonance rotary control (higher values get more 'peaky')
-- the 'Broad/Narrow' switches, which controls the number of filter sections that are used,

The Auto-Panning block, which contains:
-- the row output/mute switches (output when the 'X' is light, muted when the 'X' is dark),
-- the UI Widget for the pan position and LFO modulation, as described above,
-- the LFO rate rotary control (which is almost stopped at the slowest speed!).

On the far right hand side, common to both channels, then there is a Dry/Wet mix rotary control, as well as memory buttons which can be used to ave your favourite settings. Just shift-click on a red square to save (or a grey square to over-write), and click on a grey square to recall that memory setting.

Getting AUDhexCHORUS

You can get AUDhexCHORUS on

Here are the instructions for what to do with the .amxd file that you download from

(In Live 10, you can also just double-click on the .amxd file, but this puts the device in the same folder as all of the factory devices...)

Oh, yes, and sometimes last-minute fixes do get added, which is why sometimes the blog post is behind the version number of

Modular Equivalents

In terms of basic modular equivalents, then AUDhexCHORUS would require two high-pass filters, two low-pass filters, two band-pass filters, six frequency shifters, six LFOs, six panners, some utility switches, and two mixers, giving a total of about 28 ME. It is interesting that this is also a 'wide' device in MaxForLive!

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