Klevgrand have introduced Kuvert – Swedish for envelope – which is a plug-in envelope shaper effect available for iPad and Mac/Windows (AU/VST) typically priced at $7.99 for the iPad version and $29.99 for the AU/VST version.

In essence Kuvert allows you to draw 5 different envelopes for volume, hi-cut filter, lo-cut filter, glitch and delay. The envelopes can be set up to 8 bars in length and can be drawn on a grid using bars with different resolutions, freehand or a mixture of both. The envelopes are looped and altering the length can give unusual effects.

The interface is clean and very well laid out which is what we typically see with Klevgrand software. Because they design software for iPad, this results in a touch interface designed for ease of use rather than replicating an existing physical interface.


The drawing window comprises the main part of the display with grid and envelope length like an x and y axis. Controls are arranged underneath with separate dials for each envelope. The volume has a range setting, both filters have range and resonance settings, the glitch control affects the timing or latency of the audio signal and the delay has controls for delay time and feedback with a small adjacent display window for setting the hi-cut and low-cut filter settings and resonance for the delay unit.

The envelopes sync to your DAW tempo and the length is set in beats so for a 4:4 bar the envelope length should be 4 to loop at the same starting point. Choosing a different length setting will alter the loop starting point and apply the effects at different points giving the potential for variation and some unusual results. To switch between the effects simply click the label beneath the drawing window or one of the effect control parameters.

Using grid mode to draw envelopes gives a step effect and there are different resolution settings. Turning this off allows you to draw curves freehand giving much more control over the shape of the envelope. Both modes are useful for different purposes and it’s an excellent feature to allow a combination of both to create some really interesting effects.

The effects are explained below.

Alters the value of the incoming signal based on the envelope value although it only lowers the volume. The range parameter determines how much the volume envelope will affect the audio. (For example if you use bars, the maximum range gives a gated effect whereas a smoother kind or tremolo effect results when the range is reduced).

Hi-Cut Filter
Alters the frequency of a High Cut filter. The envelope max value always equals 20kHz, but the min value depends on the Hi-Cut filter range parameter. If the
range is set to max, the envelope min value equals 20hz. If the range is set to
min, the envelope min value equals 20kHz (there will be no changes to the output sound). The resonance knob sets the filter resonance.

Lo-Cut Filter
Alters the frequency of a Low Cut filter. The envelope min value always equals 20Hz, but the max value depends on the Lo-Cut filter range parameter. If the range is set to max, the envelope max value equals 20kHz. If the range is set to min, the envelope min value equals 20Hz (there will be no changes to the output
sound). The resonance knob sets the filter resonance.

This alters the playback time of the incoming audio. The envelope maximum is the current time and the minimum value represents the past determined by the range setting.


This alters the send level to a tempo sync delay. The envelope minimum value means that zero gain and envelope maximum sends the full input signal. Delay time is set in steps of 1/16th and feedback gain can be set. The filter module is a small display with two circles which are dragged horizontally to alter frequency and vertically to alter resonance.

Kuvert is very easy to use and really encourages experimentation. Whilst some of these effects can be done in a DAW using in-built effects, the advantage of Kuvert is that all the effects are together on one interface and you can see at a glance where envelopes overlap and edit them in real time. The bar length setting also allows some ‘polyrhythm’ type effects with looping envelopes affecting different parts of the audio each time. Drawing bars tends to result in a stuttery type of sound, curves give a smoother transition.

I’ve really enjoyed using Kuvert and found it effective on percussion, synth / bass and drone type sounds. It can produce subtle to more extreme filter sweeps; gated and smoother, subtle volume control; subtle to complex delays and the glitch effect can also be subtle to a more complex tape-stop kind of effect. Using a combination of several effects with different envelope lengths can create a great subtle movement or more extreme glitchy type sounds. I’ve created an album embedded at the top of the post to highlight some of the effects that Kuvert can produce on these type of sounds. These were recorded live in Sensomusic Usine Hollyhock 3 with changes made in Kuvert during the recordings.