# CoVariant — MIDI to CV/Gate Audio Units

> MIDI to CV/Gate audio units for controlling analog synthesizers and modular systems. (iPhone/iPad app by Alan Clifton.)

- Source: https://appshunter.io/ios/app/covariant/id1499681559 (this page in markdown: same URL + `.md`)
- Developer: [Alan Clifton](https://appshunter.io/developer/395774303)
- Category: Music, Music
- Price: $7.99
- Rating: 5.00/5 from 5 App Store ratings · 3 written reviews indexed
- Age rating: 4+
- Requires: iOS 12.0 · 11 MB
- Languages: American English
- Released: 2020-03-10
- Data updated: 2026-06-10
- Monetization: paid
- User reviews in markdown: https://appshunter.io/ios/app/covariant/id1499681559/reviews.md

## What is CoVariant?

CoVariant is a set of audio units that turn a DC coupled audio interface into a MIDI to CV converter. The audio units convert MIDI note and controller data and timing information from the host app to control voltages that can be used to control external analog synthesizers, modular systems, sequencers, drum machines or other CV controlled analog equipment.

The app contains five audio units that can be loaded by AU host apps. Please note that these audio units do not run stand-alone: they require a compatible host to work.

CoVariantAU is a MIDI to CV converter that provides outputs for CV/Gate, two MIDI controllers and two ADSR-type envelope generators. It supports last, low and high note priorities, multiple or single trigger modes, legato or continuous glide/portamento with constant rate or constant time modes and pitch bend. The controller outputs can be set to note velocity, aftertouch or any MIDI continuous controller number (0 to 127). Controller outputs are smoothed to prevent any stepping.

TriggerAU is a simplified version of CoVariant AU that responds to MIDI note events and provides outputs for gate/trigger and one MIDI controller. Its primary purposes are to control drum modules or to convert MIDI controller data to control voltages.

ClockAU provides outputs for Clock and Run/Stop/Reset, allowing analog sequencers and DIN Sync drum machines or synthesizers/sequencers to be synchronised to the tempo and transport of the host app.

PolyphonyAU is a MIDI processor that functions as a polyphonic voice controller for multiple instances of CoVariantAU.

EncoderAU allows the use of the Expert Sleepers ES-5, ES-40, ESX-8GT and ESX-8CV eurorack modules. The outputs from the other AUs (or any other software capable of acting as a CV/Gate souce) may be routed to the hardware outputs of the ES / ESX modules.

The Audio Units require a host application that supports multi-channel audio interfaces. Please note that GarageBand lacks this ability and so is not suitable. The accuracy of the ClockAU is dependent on the timing and transport state data provided by the host app. EncoderAU requires a host app that can support an AU with multiple input busses (AUM by Kymatica fully supports this AU).

## Key features

- MIDI to CV/Gate conversion
- Control voltage generation
- Envelope generators (ADSR)
- Clock and Run/Stop/Reset outputs
- Polyphonic voice control
- Eurorack module integration

## Recent user reviews (3 of 3)

All indexed reviews: https://appshunter.io/ios/app/covariant/id1499681559/reviews.md

### 5/5 — Works a treat with modern MOTU Interfaces

*2022-08-12, version 1.2.2*

This has been indispensable to ensure that my modular stays synced with things on my iPad!

### 5/5 — Drives my Expert Sleepers ES-8 perfectly.

*2021-02-04, version 1.1.0*

i use Expert Sleepers ES-8 audio interface to send CV and gate to my modules via CoVariant and AUM. Absolutely seamless operation.

### 5/5 — Must have if you use your iPad with modular synths!

*2020-10-21, version 1.1.0*

Hello audio clock sync!

## Frequently asked questions about CoVariant

### What is CoVariant?

CoVariant is a set of audio units that convert MIDI data from a host app into control voltages (CV/Gate) for analog synthesizers and modular systems. It requires a compatible host application to function.

### Does CoVariant work as a standalone app?

No, CoVariant audio units do not run standalone. They require a compatible host application that supports multi-channel audio interfaces to load and operate them.

### What kind of analog equipment can CoVariant control?

CoVariant can control external analog synthesizers, modular systems, sequencers, drum machines, or any other analog equipment that accepts control voltage (CV) signals.

### What are the different audio units included in CoVariant?

CoVariant includes CoVariantAU for MIDI to CV/Gate, TriggerAU for simplified control, ClockAU for synchronization, PolyphonyAU for polyphonic control, and EncoderAU for Eurorack module integration.

### What are the system requirements for CoVariant?

CoVariant requires a host application that supports multi-channel audio interfaces. GarageBand is not suitable due to its limitations. It is available on iPhone, iPad, and iPod.

### How accurate is the ClockAU?

The accuracy of the ClockAU is dependent on the timing and transport state data provided by the host app. For optimal performance, ensure your host app provides stable and accurate timing information.

### What is the price of CoVariant?

CoVariant is available for a one-time purchase of $7.99. There are no in-app purchases or subscription fees associated with this application.

### When was CoVariant last updated?

CoVariant was last updated on July 24, 2023, with version 1.2.3. This indicates ongoing support and potential for future improvements.

## Version history (last 5 releases)

### 1.2.3 — 2023-07-24

This version fixes various issues when the AU's are running under Logic Pro:
CoVariantAU and TriggerAU: could stop responding when Logic is looping.
ClockAU: could be 8ms out of sync with Logic's audio and could stop responding when Logic is looping.
PolyphonyAU: would fail validation.
Also fixes the broken hyperlinks in the documentation index.

### 1.2.2 — 2022-01-21

This version fixes a problem in EncoderAU where routing the same input to an output on the host ES-3/8/9 and to an output on an attached ESX-8CV would result in different voltages being produced by the ES and ESX modules, and updates CoVariantAU's manual calibration so the default values are suitable for the revised EncoderAU. This brings the behaviour of EncoderAU into line with Expert Sleepers SilentWay and VCV Rack encoders.

Any presets saved that used the previous default manual calibration in CoVariantAU to drive an ESX-8CV will need to be updated to keep the tuning correct. In CoVariantAU enter 10.0 in the Maximum Interface Voltage field, then tap the Create button to generate a correct calibration.

### 1.2.1 — 2022-01-15

Fixes a problem where text would be truncated if the Bold Text accessibility option was set.

### 1.2.0 — 2021-11-16

1.2.0 adds two new audio units:
• PolyphonyAU is a polyphonic voice allocator that can control multiple instances of CoVariantAU.
• EncoderAU allows the use of the Expert Sleepers ES-5, ES-40, ESX-8GT and ESX-8CV eurorack modules. The outputs from the other AUs (or any other software capable of acting as a CV/Gate souce) may be routed to the hardware outputs of the ES / ESX modules.

### 1.1.1 — 2021-04-30

Adds automation for the following parameters:

CoVariantAU:
• Bend range
• Glide mode, type and time
• Controller 1 range
• Controller 2 range
• Envelope 1 attack, decay, sustain, release and range
• Envelope 2 attack, decay, sustain, release and range

ClockAU:
• Multiplier and divider
• Swing

TriggerAU:
• Controller range

Bug fixes:

CoVariantAU:
• Fixes a problem where selecting the same controller in each of the modulation sections would result in the second modulation section producing no output.
• The output of the envelope generators will now change as the sustain level parameter is changed, either via the interface or via automation.

ClockAU:
• Fixes a problem where changing the multiplier, divider or swing would result in an incorrect pulse duration if the value was set to 50%.

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## More apps by Alan Clifton

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All apps by Alan Clifton: https://appshunter.io/developer/395774303

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-06-10.*