Let me explain what's happening and offer a few options. This is going to be long, so please bear with me.
First it is important to understand something about how layers work. What you see in the UI in that row of yellow bars are called the play layers. These are audio loops that have finished being recrorded. The one that is highlighted (usually on the right) is the active layer and is what you hear. You can move back and forth in the layer history with Undo and Redo.
There is also another invisible layer called the record layer. The record layer is what is accumulating the changes you are making while the active play layer is being played. If you have Overdub on for example, the record layer is receiving whatever is comming in from the audio interface and merging that with what is in the play layer. When the play layer reaches the end, if there is anything new in the record layer, the record layer is shifted. The record layer is moved to the play layer list, and a new record layer is created, ready to receive more overdubs. In the UI, you will see another yellow layer bar added to the list.
If the play layer reaches the end and the record layer does not have any new overdubs in it, then this shift does not happen. The play layer returns to the start and starts again, and the record layer is reused for another pass.
You might visualize this as a composer writing music on sheets of staff paper. Every time the composer finishes a page, they hand it to the band that begins playing that page, and the composer starts writing a new page. If the composer gets distracted and decides not to write anything new, the band just keeps playing the last page.
Now, imagine that you have recorded a loop and made two layers containing overdubs. Overdub mode is
not currently on. Mobius is just playing the last "page" over and over. In memory it looks like this:
P1 P2 P3 R
*
Where P1, P2, and P3 are the three play layers and R is the invisible record layer. The star indicates which of the layers/pages that is being played. The record layer is empty.
Now you press Undo. For simplicity let's assume that redo is disabled so pressing Undo once results
in this:
P1 P2 R
*
P3 was thrown away, and the previous play layer P2 is now active. The record layer is still there, but it is still empty.
Now turn Overdub on, and let it run for awhile. The layers look like this:
P1 P2 R+
*
P2 is playing but the record layer now has something in it. It is waiting for P2 to reach the end, then whatever is in the record layer will be shifted and R+ will become P3 and a new empty R is created.
While you are in this state and before P2 reaches the end you press Undo. What happens?
There are two choices.
- 1: you forget whatever was in R+ and keep playing P2
- 2: you forget whatever was in R+ and you throw away P2 and move the active play layer back to P1.
In the UI since you can't see this invisible R+ record layer, it looks like you should always be moving backward in the layer list whenever you press Undo. But Mobius actually uses approach #1. It first checks to see if there is anything in the record layer, and removes that first. Only if the record layer is empty does it start removing the old play layers.
This may look like Undo isn't doing anything since you don't see the highlighted layer bar move. But it is actually doing something, it is erasing the R+ record layer and preparing it for something new.
To understand why this can be useful, here's an example. You've spent a long time evolving the loop into something that has multiple "parts". The first layer has a drum beat, the second layer has a bass pattern, and the third layer has some chords.
P1:Drums P2:Bass P3:Chords R
When P3 is playing you hear it plus all the layers that came before it, so you are now hearing the
combination of the chords, bass, and drums. Now you want to record a solo part. You wait for P3 to loop back to the beginning and turn on Overdub. But you hit a wrong note and want to start over. The layer list looks like this:
P1:Drums P2:Bass P3:Chords R:Bad Solo
*
You press Undo. If we took approach #2 above, then not only would it remove the R:Bad Solo layer, it
would also throw away P3:Chords, and move you back to P2:Bass. This isn't usually what you want, you just want to throw away the bad solo and start over, without losing any of the previous layers containing the solo background.
So what's the problem?
Overdub is an unusual mode. Once you turn it on it stays on, which means that the record layer will always have something in it. As soon as you press Undo to throw away R:Bad Solo, you will have an empty record layer. But since Overdub is still on, it immediately starts putting new content into the record layer. If you press Undo again, it says hey, there's something new in the record layer, I'll throw that away first. Immediately after that, Overdub again starts putting things into the record layer and this pattern repeats until you turn Overdub off. In the UI it looks like nothing is happening, but what is actually happening is that it is clearing the record layer over and over again.
A similar situation exists if you are using the Feedback control to reduce feedback. Turning down feedback is in effect a modification to the layer that is playing. It is continually copying the play layer into the record layer and reducing its volume.
Sounds like we're in a pickle, what can be done about this?
First there is an obscure parameter that few people know exists called Noise Floor. What this does is set a sound level threshold that any overdub must exceed in order to be considered significant. If you are playing an electronic instrument like a keyboard, then unless you are pressing a key, no sound is being produced so even if Overdub is left on, nothing is being put into the record layer. When the play layer reaches the end it sees the record layer is still empty and doesn't generate a new play layer. Undo will work as expected since the record layer is always empty.
If you are playing an accoustic instrument like a guitar however, it is common to have a small amount of "string noise" as you move your hands over the strings. You may not be "playing" anything you want recorded but the instrument is still generating a soft sound that Mobius hears. The same situation exists when recording with a microphone, you may not be singing anything you want recorded, but the mic will still pick up a small amount of room noise or leakage from other instruments.
To prevent Mobius from thinking that every little sound that comes in from the audio interface is worthy of putting into the record layer, you need to raise the Noise Floor parameter. What this number is will depend on your instrument and playing style. In the past it has defaulted to the mysterious nuumber 13 which wasn't chosen through any scientific method, it's just a number that worked for me. You will need to experiment to find a number that works best for you, it probably doesn't need to go above a few hundered, but it should never be zero.
If you have Noise Floor set to something around 100 and you are still getting the "undo does nothing" problem, try to 200, then 300 see if that helps. It's possible there is a bug there. The number you are entering is a raw sample level number which assuming a 16-bit audio interface will max out at around 32,000. But you should never have to go above 1000.
While exploring this, I did find something new that could be added that might help here.
One of the things Undo does before it starts throwing away layers is cancel modes. If you were in Multiply mode for example, it would first cancel Multiply and throw away the record layer containing the multiplication. Then it would start removing old layers.
Overdub could work the same but it doesn't. If you have Overdub on, then there will usually be something in the record layer that will be thrown away first. Undo could not only throw away the record layer but it can also cancel Overdub mode and return you to Play mode. This will prevent this immediate modification of the record layer that causes the never ending undo. In the Bad Solo example, it gets rid of the bad solo, and gives you time to collect your thoughts, When you are ready you then have to press Overdub again to begin recording the Good Solo.
How does that sound?