User Manual
Mutronics Mutator
Intro
Overview
Knobs and Switches
Operation of the Mutator
Envelope Follower
Filter Sweep
The Low Frequency Oscillators (LFO)
Block Diagram
Extended Features
Credits
The Mutronics Mutator was an analog hardware unit that gained a lot of popularity among musicians, music producers and recording engineers in the 1990s and early 2000s. It can clearly be heard on records that had a big part in defining that era, with artists such as Radiohead, U2, Nine Inch Nails, Depeche Mode, Chemical Brothers and Daft Punk among its users. Production of the hardware ceased in 2007 since a vital component was discontinued by the component manufacturer, and it has only been available in the second hand market since then.
In the development work with the Mutator plug-in, Softube has worked closely with Mutronics to ensure that every little nuance of the original unit is faithfully captured. But we also made a few modern additions that makes the plug-in even more useful.
The Mutator is a stereo analog filter and envelope follower with full control facilities. It contains two independent voltage controlled filters, similar to those found in analog synthesizers, which can be used to treat any external sound source. Each filter can be controlled from its own associated low frequency oscillator (LFO) and/or its own envelope follower section. The envelope follower essentially controls the filter and/or volume based on the amplitude of the incoming (internal) sound source, or on an external sound source that is fed into the unit’s sidechain. This external signal can be any audio source, eg. a drum sound, a guitar, a synth, a sampler output, or even a microphone. Thus the envelope characteristics of one sound can be superimposed onto the filtering contour of another.
Another switch on the envelope follower selects envelope follow mode or gate mode—in which the circuit detects whether a signal is above a certain threshold level before switching on.
In gate mode, the device can operate much like a dedicated noise gate unit, with the added capabilities of the analog filters. The LFOs have four different sweep waveforms each and may be switched via a stereo link to produce stereo panning effects.
The Mutator has two channels. The upper row of buttons control the left channel, the second row controls the right channel. It is possible to synchronize the LFO of the left to the right channel, as well as to the DAW host’s song tempo.
The lowest row of knobs are additions Softube made to the plug-in, that were not part of the analog hardware. These include tempo syncing to the DAW host and a Mix button that lets the user blend the original sound with the mutated.
The front panel controls for the Mutator are identical for both channels, with the exception of the Link switch which is detailed below.
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- Envelope follower
- LFO
- Filter section
- Left channel
- Right channel
- LFO tempo sync
- Output section
Envelope Follower
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- Env source
- Sensitivity
- Attack
- Release
- Env/Gate
- Envelope LED
Env Source: Selects which signal drives the envelope follower circuit. In INT (internal) position, the sound source is also used as the control signal for the envelope follower. So with the Env Source switch set to INT, the filter section reacts to the amplitude of the sound source itself. In EXT (external) position, the envelope curve is determined by the incoming sidechain signal.
Env/Gate: In ENV (envelope) mode, the envelope follower acts as its name implies, precisely following the amplitude of the control signal and producing a rapidly varying control signal which can be used to sweep the cut off frequency of the filter and/or volume level of the VCA. In GATE mode, the envelope follower is either full on or completely off, depending on whether the control signal is above or below the gate threshold as set by the sensitivity control.
Sensitivity: In Env mode, this sets the optimum drive level for the envelope follower circuit. Too low and the Envelope LED only glows faintly, too high and the LED is driven hard. The optimum setting is when the LED peaks in brightness at the loudest points of the control signal. In GATE mode the sensitivity control sets the threshold level at which the gate operates.
Attack: This adds an attack time (fade-in) at the front of the envelope. When set to ZERO (fully anti-clockwise) it has no effect on the envelope contour—fully clockwise it gives up to two seconds of fade-in.
Envelope LED: The brightness of this follows the envelope contour produced by the envelope follower. It is useful for setting the sensitivity control and visually displays the effects of changing the Attack and Release controls.
Release: This adds a variable release “tail” to the envelope. Even after the control input signal has died away, up to five seconds of fade-out may be added by this control. Setting this control to small amounts can be useful for smoothing out rapidly changing envelopes when in ENV mode.
LFO (Low Frequency Oscillator)
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- Rate
- Waveform
- LFO depth
- Link Normal/Invert
- VCA/Both/VCF
- Env sweep
- Cut off frequency
- Resonance
- Rate LED
- Link Out/In
- VCA In/Out
Rate: This changes the sweep rate of the low frequency oscillator, from about one cycle every ten seconds to 100 cycles per second. Note that when the Link switch is on, only the Rate control of the left (upper) channel has any effect as it is being used to control both channels.
Rate LED: A bright LED indicates that the LFO is at the peak of the waveform (high pitch, if it controls the frequency, or high volume if it controls the VCA).
Waveform: Selects between the four available low frequency oscillator waveforms—TRIANGLE, SQUARE, RAMP UP and RAMP DOWN. Note that when the Link switch is on, only the Waveform control of the left (upper) channel has any effect as it is being used to control both channels.
LFO Depth: Determines the amount of LFO sweep sent to the filter and/or voltage controlled amplifier.
Link Normal/Invert: Only on the left channel! Via the Link In/Out switch, the LFO of the left channel can be sent to the bottom channel (right). The Link Normal/Invert switch inverts the output of the left LFO, which is being sent to the right channel. This means that every time the left channel LFO is at its peak, the right channel’s LFO is at its lowest phase.
Link In/Out: Only on the right channel! When set to IN, The left channel LFO is sent to both channels (for stereo effects). This means that the Rate and Waveform settings of the left channel affect both channels. When set to OUT, the LFOs affect their respective channel. Please note that all other settings are still active for each channel, Link In/Out only links the two LFOs.
VCA/Both/VCF: Selects whether the output of the LFO sweeps the voltage-contolled amplifier, the voltage-controlled filter, or both simultaneously.
Filter Section
Env Sweep: Determines the amount of filter frequency sweep (up or down) being sent to the voltage controlled filter from the envelope follower.
Cut Off Frequency: This sets the centre roll-off frequency of the voltage-controlled filter.
Resonance: Sets the Resonance (or Q) of the VCF. High values produce self-oscillation.
VCA In/Out: Selects whether the final output goes through the voltage-controlled amplifier or is taken from the VCF output.
Tempo Sync
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- Tempo sync On/Off
- Tempo sync
- Width
- Dry/Wet mix
- Volume
Tempo Sync On/ Off: Setting Tempo Sync to ON means that the LFO rate of both channels are synchronized to the DAW host’s tempo. With this set to ON, the Rate knobs of both channels are deactivated.
Tempo Sync: Allows the user to set the speed of the LFO in sub divisions of the DAW host’s tempo.
Output Section
Width: This is essentially a Mid/Side matrix. Set to 0 (noon), the channels are panned hard left and right, respectively. When turned counter clockwise, the channels are both panned gradually towards the center. Both channels reach the center when the knob is turned fully counter clockwise. Turning it clockwise increases the apparent spread of the channels, making them sound as if they are wider than the actual loudspeaker placement.
Dry/Wet Mix: Turned fully clockwise, you will hear only the sound of the Mutator itself, which is how the original hardware worked. By turning the knob counter-clockwise, you can blend in the original, unaffected sound source to your liking.
Volume: Sets the overall output volume of the Mutator plug-in.
Even though the Mutator has a lot of knobs and switches, it’s really very easy to operate. Basic idea is this:
What do we want to change? Amplitude and/or cut-off frequency?
We can change the amplitude by enabling the VCA (voltage controlled amplifier), or change the cut-off frequency of the filter by enabling the VCF (voltage controlled filter).
How do we want to change it?
We can change it either by letting the “loudness” of the input signal determine the change, by using the envelope follower. Or we can let a low frequency waveform, the LFO, determine the change. Or both at the same time.
As previously mentioned, an envelope follower continuously tracks the amplitude of a signal and uses this envelope contour to control the cut off frequency of the filter. The signal that forms the base of this process is called the control signal. The control signal can either be the incoming signal itself (Env Source is set to INT) or an external signal that is fed to the Mutator using the sidechain functionality (Env Source is set to EXT). Extracting the countour from the internal signal could for example be used to create an auto-wah type of effect, where the louder parts of the sound source makes the cut off frequency of the filter move upwards.
A use case for the EXT setting would be to insert the Mutator on a piano track, and have the filter envelope on the piano be controlled by a drum loop on another track. In this case, the filtering on the piano would occur in time with the drum loop. Please refer to your DAW manual for instructions on how to set up a plug-in to accept an incoming sidechain signal.
Setting Sensitivity Control
If the mode switch is in ENV position (and Attack and Release set to 0), turning up the Sens control will cause the LED to light when a signal is present—its brightness following the loudness of the signal.
For optimum performance, set the Sens control so that the LED reaches maximum brightness when the signal appears loudest. You may have to back the dial off slightly counter clockwise, as driving the circuit too hard will cause the LED to stay on maximum brightness even if the signal strength isn’t quite at maximum.
Gate Mode
If the mode switch is now flicked to the GATE position, the LED will come on at maximum brightness when a signal is present and be completely off when the signal falls low. Thus the output of the envelope follower will look like the diagrams below depending on the switch position.
Attack and Release in GATE Mode
In GATE mode, increasing the Attack and/or Release controls will change the shape of the output as shown below.
As you can see, a versatile range of envelope shapes may be constructed from the original gate shape.
Attack and Release in ENV Mode
In ENV mode, the Attack and Release controls work as described above, but super-impose their contours on top of the original envelope shape of the signal. This can be very useful for smoothing out fast “wobblers” from a complex envelope!
The output of the envelope follower section is sent to its voltage controlled filter via the envelope sweep control in the filter section. This control has a centre zero (at noon) with both positive and negative sweep amounts available. Thus the arriving envelope contour can sweep the filter cut off frequency up or down from its original setting—which is determined by the Cut Off knob.
The same incoming envelope could produce entirely different effects on the sound depending on the settings of the Env Sweep and Cut Off controls, for example:
If the Env Sweep control is set to 0, the filter cut off frequency will be manually changed by the Cut Off control.
The Resonance control allows a variable resonant peak to be added to the filter response, similar to that produced by an analogue synthesiser filter. At low settings the sound will appear fatter with subtle treble roll-off, much like a tone control. At higher settings a noticeable “twang” will be heard as the filter is swept, and at the highest settings the filter will begin to self-oscillate at its cut off frequency.
VCA In/Out Switch
After the filter stage, there is a voltage controlled amplifier (VCA) which, when switched in, controls the final output volume of that channel. The VCA is driven by the output of the envelope follower with the same envelope that is fed to the Env Sweep control. If an external source is selected for the envelope follower, and the gate mode is selected, and the VCA is switched in, the treated sound will be gated in and out by the external control signal.
The filter section can be effectively bypassed by turning Cut Off full up and its resonance to zero. Set this way, the VCF becomes “transparent” and with the VCA switched in, the Mutator will function as a dedicated noise gate. If the cut off and resonance are altered, a filter sweep will combine with the gated effect.
The Low Frequency Oscillators (LFO)
The Mutator has two separate LFOs, one for each channel. The low frequency oscillators can automatically sweep the filter cut off (and/or VCA volume). Four waveforms are available: TRIANGLE, SQUARE, RAMP UP and RAMP DOWN. The sweep speed is controlled by the Rate control and the sweep range is adjusted by the Depth control.
The LFO output may be sent to the VCF cut off , the VCA level, or to both depending on the position of the VCA/Both/VCF switch.
Linking the LFOs
The LFOs of the two channels can be linked, in order to make them work in tandem. Note that the Link switches on the two channels are labeled differently and are used for different settings. The Link In/Out switch on the right channel (the second row of knobs) activates or deactivates linking. When activated, in the IN position, the LFO of the left channel affects both channels simultaneously. So with this setting, the LFO Rate and LFO Waveform of the right channel are deactivated. With this Link switch set to OUT, both channels’ LFOs operate independently of each other.
The Link Normal/Invert switch on the left channel (upper row of knobs) can be switched between NORMAL and INVERTED. In NORMAL mode, the LFO affects both channels in exactly the same way. In INVERTED mode, the LFO’s sweep is inverted for the right channel, essentially turning the waveform upside down. So every time the waveform is peaking on the left channel, it will be at its lowest level on the right channel, and vice versa.
Tempo Syncing the LFO
By turning on the Tempo Sync On/Off switch, the LFO rate controls are overrided by the DAW’s tempo information and the Rate is no longer doing anything. By switching the Tempo Sync knob you can change the full period of one waveform to become a 1/16th note, 1/8th note, quarter notes, and all the way up to 4 bars. For extreme settings (say 4 bars at 30 BPM) the waveforms of the LFO might change a bit.
Resetting Waveform
By hitting play, most DAW’s will send a reset command to the plug-in which will make the LFO start from scratch. For example, if the Tempo Sync is set at 1 BAR, you will get a different result if you start playback on the downbeat or in the middle of the bar.
The output section consists of a Volume control, a Stereo Width and a Dry/Wet Mix. If the left and right channels coming from the Mutator are very different, and you want to reduce the stereo width, the natural way would be to set the Stereo Width to somewhere between MONO and 0, but in many cases you can achieve a similar (but not exactly the same) effect by settings the Stereo Width more to the WIDE setting. The main difference between MONO and WIDE is that in both channels will output L+R in MONO, while in WIDE one L channel will output L-R, while the other channel outputs the negated signal R-L.
The block diagram is a simplification of how it really works, but a useful help to figure out which knob to adjust.
One thing to note is that the Env Sweep control only affects the envelope follower, not the LFO.
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A whole range of added control can be accessed with Extended Features. Please see the separate "Extended Features" manual for more information.
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Ulf Ekelöf – Graphics rendering
Torsten Gatu – Framework programming
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Mattias Danielsson – Technical support