Routing

The Front and the Back

Much like the components in the equipment racks of a studio, Numerology modules have two sides: a front and a back. The front has the primary user interface with various parameters that you can modify. The back has a set of "ports" that are used to connect a module to other modules.

Most of the time, you just work with the parameters on the front of the module, but sometimes you need to reach around the back to change a connection. To view the back panel for all the modules in the stack, chose the "Routing" tab of the "Modules/Routing" tab button that appears just below the stack tabs, and just above the top-most module:

Note: This discussion will make more sense if you are looking at a stack that already has some modules in it. If the stack you're looking at does not, just add any of the NoteSequencers to it.

For each module in the stack, you will see the "back panel" of that module. The height of each module will vary based on the number of ports for the module, but the ordering of modules from top to bottom always remains the same. On each module's back panel, you will see a series of ports.

Each port on a module has a name and a circular "connection point". Input ports have their connection point on the left of the port control, output ports have their connection point on the right. If a connection exists between two modules, you will see a colored cable between the two modules. Each type of data stream has its own color:

• Clock : Red
• MIDI : Green
• CV : Orange
• Audio : Blue

You can connect one port to another by dragging the mouse from one connection point to another. It is possible to connect more than one source to a single destination and Numerology will automatically merge the data appropriately: CV and Audio signals are mixed, MIDI streams are merged. You are not allowed to merge Clock signals.

To remove a connection between two modules, either control-click (hold down the control key and click the mouse), or right-click (click the right-most button on a 2-button mouse), to bring up a contextual menu that will have commands for disconnecting any connections made to that port. You can disconnect a single connection, or choose to disconnect all of them.

One of the downsides of any graphical routing system is that as the number of connections goes up, the readability of the diagram overall diminishes. One of the ways that Numerology addresses this problem is by not allowing direct connections between modules in different stacks. The other way is by allowing you to rearrange the ports on a module to simplify the layout. You can do this by dragging ports around the module by clicking and dragging on the port's name.

Another option you have is to hide and show connections by type. At the top-right of the routing page there is a set of buttons you can use to show and hide cables of each type, Clock, CV, MIDI, and Audio.

Whenever you add any sequencer to a stack, Numerology automatically connects it to the "Clock" port on the Stack Input module. Since all sequencers must have a connection to some clock source, it is very easy for Numerology to know that this connection needs to be made, and can make it for you.

Similarly, when you add an Audio Unit Synthesizer to a stack, Numerology automatically connects the MIDI Input for that AU synth to the first MIDI output port it can find in the stack that lives "above" where you added the AU Synth. And it connects the Audio Output for the AU Synth module to the first Audio In port it can find "below" the module. Again, this is a very reasonable convention; there may be some cases where you do not want this behavior, but 99% of the time, this works great.

Once again, when you add an Audio Unit Effect to a stack, Numerology will add audio connections into and out of the AU Effect that seem to be the most appropriate.

But for some modules, it becomes much more difficult for Numerology to predict what connections you will want to make from one module to another. Let's say that you decide to add an LFO module to a stack. This is a relatively low-level module: It doesn't generate Audio or MIDI, and its single CV output could potentially be routed to one of many destinations in the stack. In this case, Numerology doesn't make a connection, because more often than not, there will not be an obvious way to connect it, so you have to make the connection yourself.

LFO modules also have a clock input, which they require for tracking the tempo of the project. Almost always, it should be connected to the Clock port on the StackInput module, so, as with Sequencer modules, Numerology will automatically connect it to that port.

Here is a summary of the rules that Numerology follows for auto-connection when you add modules to a stack, or move them around within a stack:

• Note Sequencers, AU Synths and AU Effects are always automatically connected when you add them to a stack.
  
  
• When you move an AU Effect in a stack, by placing it ahead of or behind another AU Effect, Numerology will modify its routing appropriately (so that it mimics an 'inline' or 'serial' routing). If you manually modify the routing for an AU Effect, which you may do if you want to setup a "parallel" routing pattern, then decide to move it later, you will have to review and adjust its routing yourself.
  
  
• Any module that needs a clock signal will automatically have that input connected.
  
  
• When you use the Add Modulation feature in the stack menu, any added modules will be appropriately connected as they are added.

When adding a new module to a stack, you can disable auto-routing by holding down the option key when adding the module.

Stack Inputs & Outputs

Looking back at the routing panel for a stack, you notice the modules at the top and bottom of the stack. As mentioned earlier, these are the Stack Input and Stack Output modules, they appear in every stack, and always appear at the top and bottom. Their job is to allow you to make connections from modules in a stack to modules in other stacks, as well as to the outside world. In this role, they are just like the patchbays that you see on the equipment racks in a studio: they allow you to customize the routing of signals from equipment within the rack to the world outside the rack.

The back panels for both the Stack Input and Stack Output (Stack I/O) modules have a similar layout, though one is focused on input, the other on output. For connections to be made within the stack, they have ports just like the other modules. For connections to other stacks or the outside world, they use menus. Internally, the Stack Input and Output modules handle the routing of those signals between the two types of connections.

The most common type of external connection you might make for a stack is to send MIDI from a Note Sequencer module to a hardware MIDI Synthesizer. Assuming that the synthesizer is connected to a hardware MIDI interface which is also connected to your computer, you can route the MIDI from your stack to it by choosing the appropriate MIDI port in the MIDI Out menu of the Stack Output module.

Note: When you add a Note Sequencer to a stack, Numerology will automatically connect its MIDI Output to the MIDI port on the Stack Output module, so that bit of internal routing should already be taken care of.

Connections for Audio and MIDI I/O, which are used very frequently, appear on both the front and back panels of the Stack I/O modules. They also appear on the Mixer Channel for each stack. In both cases, they are accompanied by little mini meters for signal monitoring.

On the back panels of the Stack I/O modules, there are more connections, these are for routing Clock and CV signals from one stack to another, for auxiliary audio routings, and a special MIDI input port for remote control over a stack.

We will cover each of these in turn, but first we should review a term: the "bus".

Busses

In the world of audio, a bus is a fixed internal connection that allows you to route a signal from one place to another. On a hardware mixer, busses are used to route audio from each mixer channel to either the main outputs, or to one or more auxiliary outputs. In Numerology, there are several busses for routing data streams between stacks, as well as to the mixer. This is how you send data streams (Audio, MIDI, CV or Clock) from one stack to another.

For instance, if you look at the Audio Output menu of the Stack Output module, in addition to the direct audio outputs on your system (labeled Out 1-2, Out 3-4, etc), you will see "Audio Bus A", "Audio Bus B", etc. If you look at the Audio In menu of the Stack Input module, you will see the same entries. This means that you can easily route audio from the output of one stack, to the input of another stack: Choose any of the busses as the output of one stack, then choose the same bus as the input of another stack.

Now that we know what a bus is, we can list the busses available to the Stack I/O modules in Numerology, and how they can be used:

Clock: Busses A-C. It is pretty rare that you might want to use more than one clock signal within a Numerology project, but if you are so inclined, you certainly can. For the most part, however, Numerology stacks are all setup to route Clock Bus A to all stacks, so that all sequencers in the stacks can have their necessary diet of clock signals.

MIDI & Audio : In addition to the external I/O options in these menus, you will find eight busses (MIDI A-H and Audio A-H). These busses can be used for routing MIDI and Audio data directly between modules. The Audio busses are also used for "Audio Auxes", which are described in more detail below.

Audio Mix : The Audio Output ports also have access to two "mix" busses, labels "Main Mix" and "Alt Mix". These output-only busses are routed throught the master faders for the project, and then to the main and alternate audio outputs. Both the master faders and the master output controls are on the Mixer, on the far-right "master" mixer channel. You are not required to use these busses --you can route audio directly from a stack to the outside world-- but they are very convenient.

Audio Auxes & Stacks

Like any good audio mixer, Numerology implements aux sends and audio aux busses. Aux sends, as are all audio mixing details, are implemented in the Stack Output module for each stack. There are 8 sends available for each stack. The send level for each aux is set via a knob on the front panel of the StackOutput module, and the routings (where the send goes), is set on the back panel. By default, the 8 aux sends are mapped to the 8 general-purpose audio busses.

All of the aux sends are stereo, and you can set a send to be pre or post fader by choosing "Advanced Settings" from the action menu on the front panel of the Stack Output module.

To use an aux send to feed audio from one stack to another, choose one of the busses to use, set that as the audio input for the target stack (where you want to send the audio), and adjust the corresponding aux send knob on the source stack.

Aux Stacks

To make it a bit easier to create stacks to use for auxilliary processing, Numerology 2 has a type of stack that you can create specifically for this purpose. In the stack menu, there is an option to create a "New Aux Stack". An Aux stack has the following properties:

• When they are created, their audio inputs are automaticaly connected to an Audio Aux bus. They connect to the first Audio Aux not already used by another Aux stack.
  
  
• Their default names match the aux sends that can be used to send audio to them.
  
  
• They are added to a project such that they always appear after the regular stacks. In addition to keeping them grouped together, this ensures that no unncessary delays are introduced when feeding audio from a regular stack to an aux stack.

Routing and Stack Presets

Most of the time, when you are working with studio equipment, the connections between the various pieces of equipment (from instruments to preamps, the mixer, outboard equipment and effects) is constant. It may change from one song to another, but generally not during a single song. The same is true by default for connections within Numerology stacks: you make them, and they stay that way until you add or remove modules, or make changes yourself.

However, you do have the option of allowing connections to change along with the presets you create for a stack. This is very much an advanced feature, as it can cause headaches if you are not careful. To enable this feature for a stack, bring up the Stack Detail dialog by double-clicking on the Stack's tab, or use the "Edit Stack Properties" menu item in the Stack menu. Changing the "Routing Is Static" property from "yes" to "no" will allow you to make routing changes that are specific to each preset in the stack. In this case, "static" means "does not change" as in: "does not change when presets change".

There is an option in the action menu for each module (in the module header), to "Copy Routings To All Presets". When you have static routing for a module turned off, this command is a very handy way to have routing changes to a module copied across all its stack presets.

Module Ordering & Feedback

As has been mentioned earlier, Numerology executes the rendering of each module in order, top to bottom. It also executes the rendering of each stack in order, first to last (the Clock stack always comes first).

So the question arises: what happens when you make a connection form the output of one module, to the input of a module that preceeds (is above) it? The short answer is that it creates a feedback path. Feedback is a very interesting technique for any media type, but it is one that can be tricky to control. Numerology is relatively unique in that it is an AU host that allows you to easily setup feedback.

In fact, Numerology makes it so easy to create feedback connections that you may make them without even realizing you have done so. Often, there is no harm, but it is good to know when you are making them, as they can sometimes affect your project it ways you do not expect.

Consider the following simple case: you create a stack with 4 modules: - MonoNote - Dls Synth - AUDelay - AULowpass

And you have made a manual feedback connection from the output of the AULowpass to the input of the AUDelay:

So what happens when Numerology renders all this?

In order of execution, here are the basic steps:

• Render the MonoNote: generate MIDI to its MIDI Out port
  
  
• Render the DLS Synth: read MIDI From its MIDI In port, generate audio to its Audio Out port.
  
  
• Render the AUDelay: read Audio from its Audio In port, which happens to have two connections, one from the DLS Synth, one from the AULowpass, so the AUDelay module reads from both: the audio generated from the DLS Synth (which may contain the first note), and also from the AU Lowpass. But the AULowpass has not ben rendered yet on this pass. So what happens is that the AUDelay reads audio that was generated on the previous render pass. On each render pass, some numbef of audio samples are generated, the same number as set for the audio Buffer Size in the Preferences, typically 64, 128, 256 or 512 samples. So the AUDelay is reading the previous samples generated by the AULowpass. No problem, it reads them, applies its delay algorithm, and puts the samples in its Audio Out port.
  
  
• Render the AULowpass : it reads its Audio In port for audio samples, applies its filtering algorithm, and writes them to its Audio Out port.

The buffer of audio samples generated by the AULowpass modules will be the audio output for that Stack, and they will also be used by the AUDelay module during the next render pass.

So when you create a feedback connecton from one module to another, you are creating a bit of a delay in time: The input side of the feedback connection is reading data that were generated previously. For audio signals, this can create a 'tinny' sound whose sound level is difficult to control. For CV signals, it most-often just means that a short delay is introducted from the producer of the CV signal to the consumer of it. In many cases, that is not problem, but when the CV signal is a Gate signal, then it may definitely cause delays in other modules (such as generating notes), such that it is very audible, and sometimes hard to figgure out. So it is recommended that you follow this rule:

Avoid creating feedback connections with CV streams unless you specifically intend to do so. It is relatively easy to avoid: just place all the modules that generate CV streams ahead of the modules that consume them.

If you know how to work with audio feedback, remember that it is often useful to have a delay longer than just a few samples within the feedback. It is also recommended that you use the Audio Feedback Assist module to help control audio levels in the feedback path.