UAD Manley VOXBOX Plug-in Analysis


Introduced in 1997, the Manley VOXBOX combines the best of Manley’s audio designs, including their high-fidelity tube mic preamp, vactrol optical compressor, Pultec-style passive EQ, and de-esser/limiter into a formidable 3U package. Featuring Manley’s legendary boutique build quality, including in-house wound transformers, the VOXBOX stands alone as a premium tube-driven toolbox for outstanding vocal tracks.


  • Tube and transformer topology
  • Rich, smooth and silky sounding
  • Defined low end and smooth high end
  • Great for vocals, bass and synths

The VOXBOX preamp uses an all-tube amplifier circuit for gain. The stepped Gain control does not simply adjust the amount of amplification; instead it adjusts negative feedback within the preamp circuit. In addition to gain, negative feedback also affects transient response, harmonic structure, clipping, and other sonic characteristics. As such, Gain is typically used as a colour control and the Input and/or Output controls can then be used to normalise signal levels.
This control affects transient speed and accuracy, distortion, noise, output impedance and clipping characteristics. At lower gains (40 dB) the Pre Amp has a very clean quality, in some ways like solid state and is the best at minimising tube hiss. 50 tends to sound most like the source, and is very musical and real. The 40 setting can sound slightly slower, further back and more mellow by comparison. The 60 setting uses almost no feedback and can give a slightly more punchy and forward or aggressive sound. It may be a little hot for some tastes…

The VOXBOX compressor is based on a passive opto-isolator circuit with minimal components. Opto-isolators offer dynamic response characteristics that are musically pleasing when used with audio signals. The compression ratio is somewhat program dependent and non-linear, but it is generally similar to 3:1 ratios when compared to VCA-based compressors.
The compressor circuit is located in front of the preamp section, enabling dynamic control before hitting the preamp tubes.
Release Times

  • Slow (5s) - very slow release for the most inaudible compression
  • Medium Slow (2s) - typical choices for vocals
  • Medium/Medium Fast (1s-0.5s) - much like old LA-2A’s but also tuned for drums and bass. Pumps a bit when Attack is set to Slow.
  • Fast - (0.3s) - mimics the Manley Electro-Optical Limiter and works best in the range of 3 to 8 dB of compression

Passive EQ
The VOXBOX three-band, passive EQ is based on the classic Pultec MEQ-5. With two peak bands, one dip band, and greatly expanded and overlapping frequency selections, this broad-stroke EQ keeps the top end sweet, and the lows defined, yet natural sounding — even with extreme boosts and cuts.
The EQ circuitry is 100% passive. Each EQ frequency band contains only one capacitor, one inductor, a conductive plastic pot, and a gold contact switch in the audio path for pristine signal quality. There are no tubes, transistors, or other active components in the EQ circuit.

A second opto-isolator limiter is located after the EQ circuit. A passive notch filter can be applied to the limiter’s dynamic control side-chain, which enables de-ess functionality for sibilance control. Sidechain filtering can be disabled to repurpose the de-esser as a secondary limiter.
The limiter has a compression ratio of 10:1 (the ratio is somewhat program dependent) and up to 20 dB of limiting is available.

To analyse the non-linear behaviours of VOXBOX, I ran a 100 Hz sine wave through the plug-in at various settings.

100 HZ Sine -12 dB pass through VOXBOX Line 40

100 HZ Sine -12 dB pass through VOXBOX Line 45

100 HZ Sine -12 dB pass through VOXBOX Line 50

100 HZ Sine -12 dB pass through VOXBOX Line 55

100 HZ Sine -12 dB pass through VOXBOX Line 60

100 HZ Sine -12 dB pass through VOXBOX Mic 40

100 HZ Sine -12 dB pass through VOXBOX Mic 45

100 HZ Sine -12 dB pass through VOXBOX Mic 50

100 HZ Sine -12 dB pass through VOXBOX Mic 55

100 HZ Sine -12 dB pass through VOXBOX Mic 60

100 HZ Sine -12 dB pass through VOXBOX Mic 60 Transformer

Both the Line and Mic Inputs generate strong lower ordered even and odd ordered harmonics. The Line is more coloured than the Mic and produces some high ordered harmonics.

The Line circuit has a strong third (octave and a fifth) and fifth (octave and a major third) harmonic, this adds richness and depth to the source. When the preamp Gain is increased from 40, the second harmonic (octave) is gradually boosted, until it surpasses the third at a setting of 60, this adds more body to the source.

Surprisingly, the Mic Input is cleaner than the line and has a very smooth sound. Like with the Line, the second harmonic is gradually boosted but surpasses the third harmonic at an input setting of 45.

The Transformer adds negligible higher ordered harmonics.

In general, if you want a smooth sound with body choose Mic, if you want a little more colour, richness and depth go Line.

For this test I ran a drum loop through VOXBOX at various settings. I have compensated for level so that the drum loop peaks at approximately -1 dBFS for maximum resolution of the waveform in Pro-L.

Dry Drums

Drum Line 50

Drum Line 50 Transformer

Drum Line 55

Drum Line 55 Transformer

Drum Line 60

Drum Line 60 Transformer

Drum Mic 50

Drum Mic 50 Transformer

Drum Mic 55

Drum Mic 55 Transformer

Drum Mic 60

Drum Mic 60 Transformer

The VOXBOX has soft and smooth saturation behaviour in both Line and Mic modes. At the 60 setting, the upper midrange is saturated more in both modes; however, take a look at the Mic Input at 60 and 60 Transformer, the initial transients are actually enhanced rather than rounded, very similar behaviour to the API Vision.

Engaging the Transformer makes the source sound ‘sharper’ and ‘brighter’ this can be visualised on the screenshots. The transients are more defined and the hi-hats have increased in amplitude. This is because a bi-product of transformer design is that the amount of saturation increases as the signal level falls, due to hysteresis, so quieter signals end up sounding slightly richer and denser, thanks to additional harmonic content.

Dry Drums
VOXBOX Drums Dry.aif (1.3 MB)
Drums Line 50
VOXBOX Drums Line50.aif (1.3 MB)
Drums Line 50 Transformer
VOXBOX Drums Line50 Tran.aif (1.3 MB)
Drums Line 55
VOXBOX Drums Line55.aif (1.3 MB)
Drums Line 55 Transformer
VOXBOX Drums Line55 Tran.aif (1.3 MB)
Drums Line 60
VOXBOX Drums Line60.aif (1.3 MB)
Drums Line 60 Transformer
VOXBOX Drums Line60 Tran.aif (1.3 MB)
Drums Mic 50
VOXBOX Drums Mic50.aif (1.3 MB)
Drums Mic 50 Transformer
VOXBOX Drums Mic50 Tran.aif (1.3 MB)
Drums Mic 55
VOXBOX Drums Mic55.aif (1.3 MB)
Drums Mic 55 Transformer
VOXBOX Drums Mic55 Tran.aif (1.3 MB)
Drums Mic 60
VOXBOX Drums Mic60.aif (1.3 MB)
Drums Mic 60 Transformer
VOXBOX Drums Mic60 Tran.aif (1.3 MB)
Drums Comp 3dB Med/MedFast Line50 Transformer
VOXBOX Drums Comp 3dB Med:MedFast Line50 Tran.aif (1.3 MB)
Drums Comp 3dB MedSlow /MedFast Line50 Transformer
VOXBOX Drums Comp 3dB MedSlow :MedFast Line50 Tran.aif (1.3 MB)

Lets take a look at VOXBOX’s frequency and phase response at various settings
What I am looking for is the frequency and phase response of the plug-in at unity and how particular settings change this relationship.
Spectrum Colours
Yellow - noise generated by the plug-in analysis software to analyse the plug-in
White - frequency response of the plug-in at that particular setting
Red - phase shift of the plug-in at that particular setting

Line 40

Line 40 Transformer

Line 45

Line 45 Transformer

Line 50

Line 50 Transformer

Line 55

Line 55 Transformer

Line 60

Line 60 Transformer

All variations have a relatively linear frequency response and good phase response; however, the 50 setting with Transformer engaged produces the best frequency and phase response. The setting Manley recommend for the cleanest response…
The Mic Input produces similar enough responses not to bother exhausting this post with even more screenshots.

I would love to hear what you guys and girls are using this beautiful sounding plug-in on?

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I really appreciate the analysis! It’s hard to find info on the plug in version for some reason. I’ve been trying to use this plug on my vocals, mainly hip hop and rnb. I haven’t really gotten it to sound the way I’ve been looking for. I’ve heard the hardware version on a similar style and it sounds great.

For rap vocals I would recommend 60 for the pre-amp, as this is the most ‘in your face’ sounding, go with as fast time constants on the compressor as you can get away with; think of your release as a ‘front to back’ control, with quicker release times being more forward. The transformer sharpens the sound and imparts a little brightness, this may be conducive if you want more emphasis on initial syllables (great for fast rapping) with a slightly brighter overall tone, but could also sound too transient and sibilant, all depends on the source.

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Thanks Paul, Im going to try recording something soon with those settings. Ill let you know how it goes!

1 Like