Review: Mu Technologies Mu Voice 1.2 (Mac/Win)

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Those hoping for new developments in the vocal-processing market have reason to rejoice, for a new voice has entered the choir. Mu Voice 1.2 is a plug-in that tunes and harmonizes your vocal tracks. It is the flagship product of Belgium-based Mu Technologies and is delivered in VST and RTAS formats for the Mac and PC and AU format for the Mac.

Mu Voice uses a proprietary algorithm recently developed at Antwerp University in Belgium. This algorithm is distinctive in that it analyzes audio in extremely small units, which reduces latency and gives higher resolution in the time domain. Because there is a lot of variation in pitch in every note that even the most accomplished singer produces, large analysis windows create artifacts, called smearing, when the same frequency is assumed over too long a time. This is analogous to the way that a high-resolution digital photograph shows fewer artifacts than a low-resolution photograph because the low-resolution photograph uses fewer pixels, which smears the same color over a larger area.

Lift Up Your Voice

Mu Voice is easy to use, and I found it fun, inspiring, and instructive — fun because it's immediate, inspiring because the harmony voices are very realistic, and instructive because when you slide off-key, so do your virtual backup singers, greatly enhancing the tiniest error. Enable it on a vocal track, pick up a mic, and choose a preset (I recommend starting with a trio), and you'll hear several clones of yourself singing along in harmony in different ranges (see Web Clips 1 and 2). You can try this out in the free, time-limited version available from the Mu Technologies Web site.

As with any vocal-processing software, Mu Voice performs best when it's processing a clean signal, so put it first in the chain if possible, and certainly in front of any reverb or delay. Occasionally the harmonizing voices were garbled beyond recognition, but clicking on the Inversion button in the Analysis settings quickly fixed that.

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FIG. 1: Mu Voice''s interface features an area for editing Chord Schemes, a 4-channel mixer, and an area for managing presets.

Mu Voice has a 4-channel mixer with which to control the source voice and three harmony voices (see Fig. 1). By default, the second voice sings a third above the first, the third voice sings a fifth, and the last voice sings an octave. But it's easy to change the pitch of any voice within up to two octaves above or below the default pitch. With a bit more tweaking, you can change the pitch to anything you desire (more on that later).

Each channel strip has Volume, Pan, and Mute controls, as well as a Humanize slider to introduce subtle variations in pitch and vibrato and a Formants slider to adjust the timbre and character of a voice. Two drop-down menus (Filter and H.EQ) offer a variety of effects. Mu Voice's Pan slider delivers a bit more depth than left-right balancing; the manual says that the slider's parameters are based on measurements relative to the listener's nose, and to my ears it has a full, three-dimensional quality.

The Formants slider sets the contour of frequencies that characterize the timbre of a voice. You can tweak this curve without affecting a note's pitch. Moving the Formants slider to the left expands the formant spectrum, producing a more nasal, squeezed-down effect (similar to the e in ear). Moving the slider to the right narrows the formant spectrum, producing a more open sound (similar to the o in olive). The middle position preserves the formant spectrum of the lead voice.

I found Mu Voice's controls very useful for smoothing out harmony parts. As noted in the review of Antares Audio Technologies Harmony Engine and Zplane.Development Vielklang (see the April 2008 issue of EM, available at, synthetic harmonies can sound a little unnatural when soloed. Though harmonization software is not intended for this, soloing the parts helps you make subtle improvements (see Web Clips 3 and 4).

Strike a Chord

Beyond creating harmony voices at regular intervals, you can make Mu Voice follow specific chords: major, minor, diminished, sixths, sevenths, ninths, and suspended fourths. You use the two Chord menus to define chords for the source melody. One cycles through the available key signatures, and the other lets you choose a chord from your chosen signature. I found that awkward and a bit mind-numbing. Fortunately, Mu Voice also lets you select the key from your MIDI keyboard. Better yet, play a chord and Mu Voice will capture it for you.

Once you have the chords, you play the piece through in Write mode, indicating chord changes with your mouse or your MIDI keyboard. Then, in Read mode, Mu Voice will dutifully follow the song, moving from chord to chord at the appointed place.

Calling the Shots

The chord scheme is where Mu Voice gets interesting: a cell does more in Mu Voice than define the key and chord for a certain passage; it is a snapshot of all of Mu Voice's settings at that point. For example, if you've designated that a certain passage be linked with a C major chord, you can also tell Mu Voice to apply a certain preset. (A preset defines a wide variety of characteristics, from the presence or absence of an EQ filter to how many voices are singing and in which octaves.) Mu Voice comes with 36 presets, which you can overwrite without erasing the defaults, and it lets you save an additional 24 of your own. Projects, which contain both Chord Schemes and settings, are saved as XML files, and they are compatible with any version of Mu Voice on any platform.

FEATURES 1 2 3 4 5 EASE OF USE 1 2 3 4 5 AUDIO QUALITY 1 2 3 4 5 VALUE 1 2 3 4 5

In a useful touch, a preset can shift the pitch by as much as 12 semitones up or down. That lets you use Mu Voice to create counterpoint; however, it requires a lot of mental gymnastics. Mu Voice doesn't visually represent the separate voices in a piano-roll-style editor as does Vielklang or Celemony Melodyne. Both Vielklang and Melodyne require a separate process of analysis prior to creating harmonies, whereas Mu Voice operates in real time.

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FIG. 2: The MIDI keyboard panel replaces the area below the faders and lets you issue commands or enter notes and chords.

Because Mu Voice does its work very quickly, analyzing the source melody and producing harmonies with a latency of as little as 5.8 ms, it is well suited for live performances. Onstage, a MIDI keyboard opens up highly expressive possibilities. By pressing a key, you can call up any preset, jump to any spot in the Chord Scheme, and make your virtual backup singers change key (see Fig. 2).

Playing for Effect

Mu Voice comes with two effects offering a limited number of settings. (The company says more control will be added in future versions.) Filter lets you dial up nine different filter types: highpass and lowpass, which attenuate the frequencies above and below 4,000 Hz with a 6 dB slope; a telephone-line effect, which filters frequencies between 400 and 4,000 Hz (see Web Clips 5, 6, and 7); and comb and inverse-comb at multiples of 300, 600, and 1,200 Hz. The combs are most interesting — imagine waves rolling through an EQ, affecting groups of frequencies.

Harmonic EQ is based on Mu Voice's core algorithm. It lets you control the amplitude of the individual harmonics of a given sound rather than changing the amplitude of a fixed frequency range. For instance, it might alter the tenth harmonic of a given note, no matter what that note is. Harmonic EQ settings follow the melody. (Compare Web Clips 8 and 1. You'll notice that in the Harmonic EQ version [Web Clip 8], it sounds as if the voice were singing from inside a bottle.)

Though its deeper features could use refining, Mu Voice offers immediately gratifying, great-sounding harmonies, and it performs exceptionally well in real time. It is a welcome new addition to the pantheon of harmonization software, and it can only get better as it evolves.

David E. Weiss is a songwriter, musician, and self-producer in the San Francisco Bay Area.


harmony-generating software $279

PROS: Easy setup. Excellent sound quality. Powerful interface for automating presets and chords. Easy to manipulate with a MIDI keyboard. XML-based settings for compatibility.

CONS: Limited effects. Contrapuntal arrangements difficult to orchestrate.

Mu Technologies


EM's review of Antares Harmony Engine and Zplane.Development Vielklang from the April issue