Monday 11 February 2019

Fun with Frequency Shifting

Here's a surprise entry from the 'rapid gestation' pipeline - a hex frequency shifter that is totally intended to mangle spectra! This is not a scientific instrument designed to move technology towards ever higher fidelity. It joins the 'Ironic Distortion' device and a few of my other devices on the 'noise' side of the audio processing 'sine to noise' axis.

So that's the advert - but what is happening inside? (I would say 'behind the front panel', but I can't see this ever making it into real hardware!) Well, this is a 'true' stereo device, and so there are two parallel audio paths, each with 3 frequency shifters, and so it definitely qualifies for the name: 'Hex'.

But rather than follow the path forged by the many other frequency shifters that have already been created in M4L, I threw caution to the winds and went free-form, so the routing between the frequency shifters is not preset. The outputs from the upper and lower sidebands of the frequency shifters, plus the inputs to the next shifter, and the input to the auto panned outputs, all go into two routing matrices where you can connect them together as you like. The default is 'no connections', so all of those [X] toggles are dark, and there is no audio output (unless you turn the rotary control to 'Dry', of course!).

Probably a good starting point is to click on the [X] toggles for the '+' in the Left and Right routing matrices. This will route the upper sideband output of the first frequency shifter into the input of the second, and so on, through all three shifters. You won't hear anything at the output until you also route the auto-pans, which are the extra [X] toggles in the centre section between the two channels. So select the lowest of those [X] toggles to hear the full 'hex shifter' sound! This is probably a good time to set all of those pan rate controls to different values so that the stereo output will be fully spatialised!

(The two [X] toggles with arrows allow you to patch across from one channel to the other, so you can send audio back and forth between the two channels as you wish. As with many things, turning on all of the toggles is not necessarily the best approach!)

Each frequency shifter has two modes:

'Freq'  mode:

'Freq' mode does exactly what you expect - it shifts the incoming spectrum. If you click on the 'Mod' button so that the LFOs grey out then you will get the 'fixed' frequency mode where there is just a single frequency control that sets the amount of frequency shifting. If you turn on the 'Mod' button then the LFO rate and modulation depth controls will appear, and you can then wobble that frequency shift instead of it being fixed. (Oh yes, and this diagram above kind of gives the impression that there is only one LFO per pair of Frequency Shifters, whereas actually there are two...)

'Rate' mode:

'Rate' mode is slightly more unusual, and I haven't seen anything quite like it in any of the effects units that I've played with... What it does is sample-and-hold the incoming audio, and use this to shift the frequency - and it sounds really interesting and different... The 'Mod ' button has the same effect: 'off' hides the controls and mutes the LFO, whilst 'on' shows the controls and allows the frequency shift value to be modulated by the LFO.


You can use HexFrequencyShifter as a 'drone' processor, where it can turn rather ordinary bland sounds into something altogether more complicated. Frequency shifting tends to be rather destructive to sounds that have to be in tune with other sounds, and so, at first sight, this is not a device to be used for processing an instrument that will then be played alongside other tuned instruments.

But if you use the 'Wet/Dry' rotary control carefully (less than 25%, for example), then you can add small amounts of non-harmonically related distortion to your audio, which can be rather like adding pepper to food. Now, back in the 1970s and 80s, devices that added 'carefully designed additional spectral information' to audio used to be called 'exciters', and were often used to compensate for the aggressive low-pass filtering that people used to try and control tape hiss. As it happens, the HexFrequencyShifter is quite good at producing 'additional spectral information', and even to jaded ears such as mine, having spectral components of distortion moving around and across the stereo stage is quite cool! (Most of the distortion I have heard is often quite boring spatially) I will see what I can do about an audio demo on Soundcloud... But in the meantime, here's a video demo on YouTube (complete with a video titling error because I was rushing!):

Getting HexFrequencyShifter

You can download HexFrequencyShifter for free from

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 modular equivalents, then the 'Bode Frequency Shifter' was one of the modules that appeared on classic Moog modulars, although I'm not sure that they appear in many lists of 'basic' modules for a minimal modular synthesis setup! But since I added a 'Scale' device recently, then I'm going to add a 'Frequency Shifter' module as well. Based on this, then my estimate is that you are going to need 6 frequency shifters, plus 6 LFOs, plus three stereo auto-pans, which gives a grand total of about 18 ME.

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