Zebra 3 Beta Bug Reports

[Harmes]

Yes,
they are all located in the same Factory list, but the arrows switch only between 2 “random” cvs.

Not sure if this is a bug or an intention (cannot find it in the bug report list):
Insert a Modal module, click on +, now if you press any of the arrows next to Factory profile it only switches between two cvs, but factory profile isn’t affected.

I think that may be related to the current selection of profiles. The control is designed for them to be sorted into folders, so they can be browsed by folder/category. This works in a similar way for Hive's wavetables. But I guess currently they're all in one folder or so?

[ffx]

Are you sure that this is no bug?

1. This preset:

HM Yay Fifths.h2p.zip

2. Switch LFO 2 to TRIANGLE
3. Sounds very steppy now, but why?
4. Switch back to SINE, sounds way smoother now

No idea, but why it' so steppy sounding with TRIANGLE? SINE sounds more like triangle to my ears. But maybe there is no bug and all is expected, just wanted to let you check this...

[ffx]

* By "steppy" I mean the steps audible in the pitch modulution via comb module.

[Sampleconstruct]

* By "steppy" I mean the steps audible in the pitch modulution via comb module.

Right click on the LFO and check if it has some kind of quantization applied, there are numerous options.

[ffx]

Thanks, can't find any enabled quantization.

[Urs]

* By "steppy" I mean the steps audible in the pitch modulution via comb module.

Ah, so the Comb is basically like a short delay or chorus here. Modulating tune modulates the delay time.

Modulating a delay time with triangle waveform results in perceived square wave modulation of pitch.

There's a mathematically sound reason for this, i.e. it is quite logical, but I have been surprised too, when I first encountered the effect (and so have many others).

[Urs]

Ok, let's let a computer explain the math:

When you modulate a delay time with a triangle LFO, you're creating a **Doppler shift effect** - the same phenomenon you hear when a siren passes by.

Here's what's happening:

## The Core Mechanism

A variable delay acts like a virtual tape recorder where you're changing the playback speed. When the delay time increases (LFO ramp up), samples are being played back more slowly than they were recorded - the virtual "tape head" is moving away from the write position. When the delay time decreases (LFO ramp down), samples play back faster - the head is catching up.

## Why Two Distinct Pitches

The triangle LFO has two constant rates of change:
- One constant positive slope (delay time increasing)
- One constant negative slope (delay time decreasing)

Each constant slope produces a constant frequency shift. If your triangle is symmetrical, the magnitude of pitch shift is the same but in opposite directions - one pitch above the original, one below.

The pitch shift amount is proportional to the **rate of change** of the delay time, not the delay time itself. This is why you hear two alternating pitches rather than a continuous pitch sweep - the triangle has only two discrete slopes.

## The Math

The frequency shift ratio is approximately:

`f_out / f_in ≈ 1 / (1 + dD/dt)`

where `dD/dt` is the rate of change of delay time. For a triangle LFO at frequency `f_LFO` and depth `d` samples:

- Upward slope: `dD/dt = +4df_LFO`
- Downward slope: `dD/dt = -4df_LFO`

This gives you two stable pitch-shifted versions that alternate at twice the LFO frequency.

[ffx]

Very interesting, thanks for the detailed explanation. I recently looked into a lot of chorus vsts (assuming it's the same algorithmic approach), to find a replacement for the Renoise internal chorus fx. While testing those plugins, I observed the same step effect using triangle mod waveform as here, e.g. in Blue Cat's chorus. I was always assuming that Renoise chorus uses a triangle waveform, but after now rechecking, it looks more like a sine, too, hence the smooth modulation sound.

Is it possible to set the LFO to an shape which is a morph of sine/triangle, or sine/square, so "in-between-shapes"? Using the modulation curve, I assume?

[Urs]

Very interesting, thanks for the detailed explanation. I recently looked into a lot of chorus vsts (assuming it's the same algorithmic approach), to find a replacement for the Renoise internal chorus fx. While testing those plugins, I observed the same step effect using triangle mod waveform as here, e.g. in Blue Cat's chorus. I was always assuming that Renoise chorus uses a triangle waveform, but after now rechecking, it looks more like a sine, too, hence the smooth modulation sound.

Is it possible to set the LFO to an shape which is a morph of sine/triangle, or sine/square, so "in-between-shapes"? Using the modulation curve, I assume?

You can draw any shape you want in the Mappers (and drive the Mapper form a Saw or Triangle LFO)

[Urs]

(you can even copy paste a shape from the Oscillators into the Mappers)

[PieBerger]

(you can even copy paste a shape from the Oscillators into the Mappers)

Oh that's neat!

Edit: maybe that could be added into the manual!

[Urs]

Edit: maybe that could be added into the manual!

It will...

[PieBerger]

Not sure if it's a bug/design choice/WIP, but when adding a new mod slot within a source tab e.g. MSEG1, it loads a blank module, could/should this be context aware and load up with the appropriate source?

[PieBerger]

Edit: maybe that could be added into the manual!

It will...

Awesome, it's a great feature that folks don't want to miss out on

[tasmaniandevil]

Not sure if it's a bug/design choice/WIP, but when adding a new mod slot within a source tab e.g. MSEG1, it loads a blank module, could/should this be context aware and load up with the appropriate source?

We've been thinking about it. Currently, it loads a generic mod slot, same as if you create a new mod slot on the mod matrix tab.
One problem we haven't solved yet: If we can make it so that it loads with the MSEG as source on the MSEG tab, what should it load as the source when creating a new mod slot on the Osc tab?