Eventide Quadravox harmonizer plug-in: features and spec-based rating

Eventide’s Quadravox is a plug-in that layers voices shifted in pitch, up to four, to match a key and scale. You place the notes on a screen like a musical score, and there is a random function that shifts the pitch of each voice slightly to sound natural. It has more than 60 presets (ready-made settings).

A harmony and doubling plug-in makes harmonies from a single vocal, or gives it the thickness of several people singing.

In this article we compare Quadravox with 10 harmony and doubling plug-ins and rate how well it serves its purpose on three criteria. The basis is official manufacturer information.

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Summary

Among the 10 harmony and doubling plug-ins, Quadravox is rank B. The ranks run S, A, B and C, and B is third from the top. Averaging the scores for the three criteria (out of 5) gives 3.3.

Strengths

• Per-voice adjustment (4 points): you can adjust each created voice in detail to finish naturally.

Who it suits: people who want to build harmonies like writing a score, and people who want to try one at a reasonable price.

Main features of Quadravox

Four voices that follow the key and scale

Quadravox is a harmonizer that makes up to four voices at different pitches from the incoming sound, following a key and scale. Besides layering harmonies, it is introduced as a composing tool for widening an instrument or making rhythmic sequences. It can also make voices from a drum sound.

Per-voice volume, pan, delay and pitch

The four voices can each be adjusted separately for volume, pan, delay with feedback and pitch (including the type of interval). With several Quadravoxes you can combine harmonies and sequences across tracks.

Start from presets

It includes presets for many kinds of instruments, such as guitar and drums. You can also type in values to set things in detail.

Where it is useful

• Layering scale-matched thirds and fifths on a vocal
• Layering a note an octave up on a guitar riff to widen it
• Making a rhythmic phrase with delayed voices

Rating by criterion

Range of effects: 3 / 5

We check how many of harmonies, same-pitch voice layering (doubling), choir and stereo width it can make.

It layers harmonies of up to four voices to match a key and scale, and the official page also describes using it to widen an instrument.

Speed: 3 / 5

We check whether you can get an effect quickly, for example by choosing or automatic creation.

It has more than 60 presets. You place the pitches yourself on a screen like a musical score.

Per-voice adjustment: 4 / 5

We check whether you can make the created voices sound natural (for example by shifting the timing or tone of each voice).

The volume, pan, delay and pitch of each of the four voices can be changed, and a random function shifts the pitch of each voice slightly.

How we score (Harmony and doubling plug-ins)

Criterion	Basis	5 pt	4 pt	3 pt	2 pt	1 pt
Range of effects	Which of harmonies, same-pitch voice layering (doubling or choir) and stereo width are officially described	All three	—	Two of the three	One of the three	—
Speed	How quickly you can get an effect (automatic creation, just choosing, presets)	Parts can be created automatically (harmonies that follow the key or chord, or doubling from the original voice)	The effect is decided just by choosing the number or type of voices	Choose from presets	Detailed settings are needed	—
Per-voice adjustment	Features that make the created voices sound natural	Tone, vibrato, pan and more can be changed for each voice	Variation between voices, or per-voice volume and pan, can be adjusted	The tone and wobble of the whole effect can be adjusted	Volume and pan only	—

Each criterion is scored from 1 to 5 on how well the product serves one goal: adding harmonies, thickness and width to a vocal. Scores follow the conditions in the table above. So that products that make harmonies and products that double (layer the same pitch) can be compared by the same standard, there are three criteria: "Range of effects", "Speed" and "Per-voice adjustment". The basis is official manufacturer information. The naturalness of the sound has not been compared by ear, so it is not part of the score. Price is not part of the score. Features that cannot be confirmed from the manufacturer's or a retailer's description are scored as if absent. The "OBS (streaming)" column in the table shows whether the official page lists the VST2 format that the streaming software OBS Studio can use (○). OBS does not support the VST3 format. It is not part of the score.

Quadravox system requirements and getting started

Operating system	Windows 10 or later / Mac (macOS 10.14 or later)
Plug-in formats	Windows: VST2, VST3, AAX / Mac: AU, VST2, VST3, AAX
Other	An iLok account is required (no USB key needed)
Trial	14-day trial available
OBS (streaming)	Works as it is (VST2 is listed)

Checked on the manufacturer’s official pages on September 27, 2026.

Compared with other harmony and doubling plug-ins

Click a heading to sort. On a phone, the table scrolls sideways.

Read next

• MicroPitch: features and rating (rank B)
• MicroShift: features and rating (rank B)
• Harmony Engine: features and rating (rank S)
• Choir: features and rating (rank A)