Hello and welcome to the forum. You'll find people here are generally very friendly (and helpful).
The NL2X should (and does

) work fine as a controller for Ableton Live. Below I'll describe one way of using your NL2X from Ableton Live 8 (or 9).
Step 0: Plug in two MIDI cables between your MIDI interface and the NL2x
One cable goes from the MIDI OUT port on your NL2X to the MIDI IN port of the interface and the other goes from the MIDI OUT port of your MIDI interface to the MIDI IN port of your NL2X.
You likely already had this connected correctly.
Step 1: Turn off Local Control on the NL2X
You have to do this
every time you start your NL2X (and this is a good thing, which I'll come back to in a minute).
When you normally press a key on your NL2X, it sends a MIDI message out the MIDI OUT port
and it sends another copy of the same MIDI message the the
sound engine in the. When the sound engine receives a MIDI messages (either from the keyboard or from the MIDI IN port), it processes this messages and makes sound, etc. However, when you turn Local Control
off, you instruct the NL2X to no longer send a copy of this message to the sound engine.
This setting is great if you want to use the NL2X as a controller for your DAW as well as have the DAW use the sounds of your NL2X. In a way it is like chopping your NL2X in two halves; the keyboard (and front panel) and the sound engine. The keyboard controls the DAW and the DAW controls the sound engine. You can then, for example, play a piano sound in Ableton using the keyboard while you have Ableton send pre-recorded MIDI data to the NL2X's sound engine (a bass line maybe?).
Now I mentioned that it was a good thing Local Control defaults back to
on once you turn your NL2X off. If you have Local Control turned off and don't have your DAW running, pressing a key on the NL2X won't do a thing! The NL2X sends a MIDI message to the MIDI interface, but since the DAW isn't running, the message doesn't get processed and nothing gets sent back to the sound engine of the NL2X. In a sense, it will appear as if the NL2X is broken. Now imagine how many NL2X-es Nord would've gotten back if someone unknowingly disabled Local Control (and it didn't default back to
off).
You can find more info on turning Local Control on and off on page 66 of the manual.
Step 2: Set up MIDI in Ableton Live
I suggest setting up the MIDI setting for your MIDI interface as shown below, at least as a starting point.
First, change the settings in the rectangle (1). For the input, make sure Track and Remote are turned on. Track means Live will read note data from that input and on what Remote does I'll explain later (you could leave if off for now).
The Takeover Mode (2) is an interesting setting. I suggest leaving it at
Pickup (the default in Live 8, although Live 9 seems to use None as the default) for now. What this does is change the way Live reacts controller information it receives via MIDI; as such, it applies mostly to the Remote option mentioned above. Your Virus has a similar setting; when set at pickup, you need to
cross the current setting of a control when you turn a knob before the knob actually starts to have effect. When Live is waiting for you to cross that current setting, the bar at the bottom of the window will turn yellow and Live will tell you it is waiting for pickup on a specific control. You can also set it to Value Scaling, which I'll not explain here. Suffice it to say that the best setting depends on your personal preferences - try both settings when you start using the NL2X to control stuff.
You can leave the controller boxes at the top empty. Live doesn't include a control definition for an NL2X - theoretically someone could create one which might make for better integration with Live, but since the NL2X doesn't have a display which can be controlled remotely, it wouldn't be that useful.
A note on MIDI clocks: I'm assuming you want Live to generate the MIDI clock, not the NL2X. This is why Sync is off for the input and on for the output; this causes Live to use its own clock (= it is not listening for one on the MIDI input) and to send MIDI clock data via the output port (since Sync is on for that one). If you don't want Live to send a MIDI clock to a specific MIDI port, turn Sync off for the output port. If you want Live to use the clock of an external MIDI instrument, turn Sync on for the input port and make sure you turn Sync off for the output port.
Step 3: Setting up the NL2X in Ableton Live
If you haven't done so already, give each slot its own MIDI channel in the MIDI settings of the NL2X. Make sure they differ from the Global MIDI channel. I suggest setting the Global MIDI channel to 1 (may be the default) and the slots to MIDI channel 2 thru 5.
Now a bit I'm not completely certain on: if you send MIDI data to the Global MIDI channel of the NL2X, I think it will use the settings of the slot buttons (which slot is active and/or enabled) to determine which slots actually play. I'm not completely sure this actually happens; I know it does for the Stage 2, but maybe it worked differently on the NL2X. I'm to lazy to really consult the manual on this and I'm sure you'll forgive me.
The best way to control an external MIDI instrument via Ableton Live is (surprise surprise!) the
External Instrument device, which you can find under
Live Devices. Strangely, they seem to have placed it under the
Instrument category in Live 9. Same difference though.
Drag an External Instrument to an existing track or drop it to the right of the tracks to create a new one. This is shown as 1 in the image above. Now make sure you can see the settings of the External Instrument device; you may need to switch to the
Device view at the bottom right of the Live window, as it may be showing
Clip or
Track view.
Set the MIDI settings in the rectangle (2); these settings determine how Live communicates with your external MIDI device. Choose the correct MIDI interface (your's will likely have a different name) and the right MIDI channel. The right MIDI channel might be the NL2X's Global MIDI channel (probably channel 1) to start with, but you can also set it to the MIDI channel of a specific slot.
Next, choose the right audio inputs in the Audio From (3) box. If you're lucky enough to have an audio interface with plenty of audio inputs, you could give every slot on the NL2X its own output and you would probably select a mono input here. If you are mixing the output of multiple slots on a single output (the default setup of the NL2X) and you are using multiple external devices, make sure only one of these devices is recording from the same audio input. If you don't, the volume for the audio coming from that specific input may double (since Live sees it twice) and, depending on the audio interface(s) used, you may have phasing issues that sound bad.
Lastly, you may want to change the hardware latency (4). Live will auto-correct latency caused by the audio interface, but it does not know about latency introduced by the MIDI interface or by the MIDI instrument itself. Leave it at 0 for now - if you find your NL2X is playing late in relation to (mostly) soft synths, you may want to try increasing this number (say to 5-10 millisec). Especially with percussive-type sounds this latency might be an issue, but generally it isn't (unless you have a really crappy MIDI interface). Alternatively, if you have a really crappy audio interface that lies and reports the wrong latency numbers to Live, you can increase the latency for that audio interface. However, do that in the
Audio section of the Live settings, so it will apply to the whole interface.
Step 4: Automation
Unless you tell Ableton Live what to do with it, it has no idea what it needs to do incoming pitchbend, modulation and other MIDI controller information.
In general DAWs use automation to control all kinds of parameters; you can record this automation, or draw it in your DAW. You may have seen faders move about on a professional mixer in a studio; this is a very clear (physical) example of automation.
When we selected the External Instrument device, we in a way got some free goodies that tell Live what to do with incoming MIDI controller data. But I am getting ahead of myself here.
Record a new clip for the NL2X track (or whatever name you gave the track the External Instrument is in) and press some keys, use the pitch stick and modwheel and maybe turn some knobs. Once you recorded a small clip, make sure the Envelope window visible. You may need to click on the E, as shown by arrow 1. How have a look at the information in the rectangle (2) - you may want to click on the drop-down box at the top.
It will show you all the
automation information that Live recorded for you. In my case, I had a Yamaha SY99 connected which has a pitchbend and two mod wheels (CC1 and CC13). Since I have Pitchbend selected, it shows me the envelope for this automation (the clipped sine wave to the right).
You can then edit or delete this information.
This was pretty easy, since the External Instrument device set up this stuff so Live knew what to do with it. When using built-in Live devices or AU/VST plugins, it is a bit more complex; more on this in the next step.
Since the External Instrument device takes MIDI as its input, you can use MIDI Effect devices to do interesting things with the incoming MIDI. For example, you could use a MIDI Scale effect to force incoming notes to be in a particular scale.
Step 5: Using your NL2X as a controller for Ableton Live
The stuff discussed above all works if you haven't got Remote enabled for the MIDI input (see step 2). However, for the stuff in this step you need to have Remote enabled so Live knows you want to use your NL2X as a remote control surface.
When configure Live to use your NL2X as a controller, you can use controls on your NL2X to control all kinds of things in Live. Of course, you can also still use your NL2X to play on as shown in step 4.
Fancy controllers (like those from Novation of M-Audio or Ableton's Push controller) have functionality where they integrate very tightly with Live. Point at a parameter in Live and the display on the device will show you what parameter you're about to change.
With the NL2X it isn't as fancy as this, but at least it sounds
much better than those controllers, especially considering those don't make any sound. In the case of the NL2X, you will use the MIDI Learn functionality to set up which control on the NL2X controls what in Live.
To start mapping MIDI controls to Live controls, click on the MIDI button at the top right (1). Large parts of the screen will now turn blue; these areas indicate controls which you can control via MIDI. Now click on the volume for the master track (2) and move the mod wheel. You should see a new line appear in the list of MIDI mappings on the left. Now do the same for the pan control of the master track (3) and move the pitch stick. Click the MIDI button a second time to leave MIDI learn mode.
Now move the pitch stick and the mod wheel and notice how they control the volume and panning of the master track. Nifty, isn't it.
Note that not every control on the NL2X sends MIDI when you use it; the volume knob is a prime example of this. If a control does not send MIDI, it also means you can't control it via MIDI.
Go back to MIDI learn made and try some things. You can, for example, use keys to start/stop a recording, use a button to toggle a setting, etc. You can also modify the ranges in the MIDI mappings window on the left. For example, you might want to give a control a range of 25% to 100% instead of just 0 to 100%.
Lastly, have a look at the small boxes pointed out by the arrows labeled with a 4. The ones on the left show MIDI data sent by Live, while the ones on the right show MIDI data
received by Live. The top one (yellow) blinks when MIDI note is received/sent, while the bottom one (orange) blinks when a MIDI clock message is sent or received. Ableton calls these MIDI indicators.
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I hope this gives you a good explanation on how to set up your NL2X with Ableton Live.