Unity/RTcmix (uRTcmix)

October, 2019

The computer-music language RTcmix running inside the Unity game/VR/AR development environment. Windows/OSX/iOS

installing the uRTcmix package

click uRTcmix.unitypackage to download the uRTcmix package with supporting files

To import uRTcmix for use, start a new Unity project. Drag the uRTcmix.unitypackage into the Assets of your project. The resulting "uRTcmix/" folder will have three subfolders:
Drag the RTcmixmain.prefab object from your Assets up to the GameObject-instantiation hierarchy tab (where the "Directional Light" and "Main Camera" objects are located).

At this point, you will probably get an error when you add the RTcmixmain.prefab object to your object list/hierarchy: To correct this, from your top menus go to Edit->Project Settings->Player and scroll down a bit in your Inspector window. Open the "Other Settings" tab (if it isn't already). Scroll down and check the box next to the "Allow 'unsafe' Code" setting.

You're now set to use uRTcmix!

make a beep

Drag the beep.prefab object from your Assets up to the GameObject-instantiation hierarchy tab. Hit the 'play' button and you should hear an 8.7-second sine wave sound with a pitch of G-above-middle-C.

inside the "beep" object

Open up the "beep.cs" script to see how the "beep" object works. At the top of the file, you should see this Those lines of code allow the C# compiler to access the methods it needs to run the script in Unity properly. NOTE: If you use any "String" operations with Unity, you will need to add: to the above set of "using ..." lines.

Next you will see these lines: The int objno = 0; declares the objno variable and sets it to 0. This is how we keep track of different instantiations of RTcmix within Unity. Each RTcmix process we attach to a game object can have a different objno, keeping it separate from other executing RTcmixes.

The rtcmixmain RTcmix; statement declares a variable that we will use to access the RTcmix functions from the RTcmixmain object.

The private bool did_start = false; statement declares a boolean (true/false) variable, did_start; and sets it initially to "false". This is so that the "beep" script won't try to run audio until RTcmix is initialized. The objno, RTcmix and did_start variables are declared here at the top of the class definition, within the "beep" class but outside any of the "beep" methods because they will be used throught the entire "beep" class.

Next we add a new method, Awake() and a new line of code to the Start() method:

The first assignment of the RTcmix variable finds the RTcmixmain game object and then accesses the "rtcmixmain" script on that object.

Once we have made that connection, we can use the RTcmix variable to invoke the functions defined in the "rtcmixmain.cs" script. We do this in the very first line of the Start() method: RTcmix.initRTcmix (objno); to initialize the RTcmix process for the objno we want to use (in this case, "0").

We then add a single line to our Start() ethod that will send a very simple (one line!) script to RTcmix:

[note: we are assuming at least a basic grasp of the RTcmix language. See the rtcmix.org web site for tutorials and information about RTcmix.]

This sends the String (the score) in the double-quotes to RTcmix for parsing and execution. The final parameter, objno, does what it did in the RTcmix.initRTcmix (objno) case; it designates which RTcmix process to use.

Finally, because we have now fully initialized RTcmix, we set did_start = true; to allow audio processing in this script to take place.

Our finished Start() method then looks like this:

The RTcmix.SendScore(...) will trigger the 'beep'.

But you will need to add two additional methods to the "beep" class for this to work:

The initial if (!did_start) return; line will prevent audio processing from occuring if RTcmix has not been initialized yet.

The OnAudioFilterRead() method passes audio data to and from the "beep" class through the data array parameter. We hand that off to RTcmix with the RTcmix.runRTcmix (data, objno, 0); line, invoking the runRTcmix() method from the "rtcmixmain.cs" file. runRTcmix() will fill the data array with one buffers-worth of sound samples from the RTcmix process (usually 512 samples in Unity). Note the use of objno again.

The final "0" after the objno variable signals that we are only synthesizing sound, not processing any sound that comes into the 'beep' class from a previous sound-generating object in Unity. A final "1" in the RTcmix.runRTcmix() would allow us to do input signal-processing. We will discuss this later.

The OnApplicationQuit() method resets RTcmix by destroying the particular instantiation and setting did_start to "false" so that the next time we run the scene (and the Start() method is called), everything will be set up properly.

Our final "beep.cs" file looks like this:


To make a repeating beep pattern is very simple in RTcmix. We can set RTcmix to repeat the score indefinitely using the ability of RTcmix to generate a 'bang' to re-trigger the score. (A 'bang' is a notion that comes from Max/MSP and the [rtcmix~] object; it is used to trigger various operations in Max.) For this we will use the MAXBANG() RTcmix instrument. MAXBANG() takes a single parameter -- how many seconds from "now" do we generate a 'bang'.

This requires only two alterations in our original "beep" script. One is to the initial RTcmix.SendScore() score that we send to include a MAXBANG() scheduled 'bang' in the future, and one to detect when that 'bang' occurs and respond appropriately.

Our revised Start() method looks like this:

Note that we have reduced the duration of the WAVETABLE() to 0.2 seconds. This is because we are scheduling a 'bang' at 0.3 seconds after the score is sent: MAXBANG(0.3). We will have 0.1 seconds of silence between the stop of that first WAVETABLE() note and the interception of the 'bang'.

We will detect that MAXBANG()-scheduled 'bang' within the OnAudioFilterRead() method. We accomplish this by using the uRTcmix function RTcmix.checkbangRTcmix(). This function will return "1" when a 'bang' is detected at a scheduled time. The OnAudioFilterRead() method now looks like this:

By sending a MAXBANG() again when we generate the next WAVETABLE() beep, we will then intercept another 'bang' in the future, and the retriggering will continue indefinitely.

reading RTcmix scorefiles

Let's suppose we've developed a more complex RTcmix score that instantiates a simple granular synthesis process:
    hifreq = 900
    lowfreq = 500
    amp = 15000
    ampenv = maketable("window", 1000, "hanning")
    start = 0
    dur = 0.05
    for (i = 0; i < 20; i = i+1) {
    	freq = irand(hifreq, lowfreq)
    	WAVETABLE(start, dur, amp*ampenv, freq)
    	start = start + (dur/2)
If we wanted to send this using our 'imbedded string' approach we've been employing with RTcmix.SendScore(), the code would look something like this:
    RTcmix.SendScore("reset(44100) " +
    	"hifreq = 900 " +
    	"lowfreq = 500 " +
    	"amp = 15000 " +
    	"ampenv = maketable(\"window\", 1000, \"hanning\") " +
    	"start = 0 " +
    	"dur = 0.05 " +
    	"for (i = 0; i < 20; i = i+1) { " +
    	"	freq = irand(hifreq, lowfreq) " +
    	"	WAVETABLE(start, dur, amp*ampenv, freq) " +
    	"	start = start + (dur/2) " +
    	"} ";
which is pretty ugly and fairly difficult to modify/debug. We can make things a little easier by using the
scoralyzer command to pre-format our RTcmix script into a valid C# string variable, but it would still be annoying to edit. There is a better way: if we save the original RTcmix code for the granular process into a text file, perhaps "granular.txt", we can add it as an asset to our Unity project and load, read, use, and edit the file from within our Unity development environment. NOTE: These files have to have the ".txt" extension for Unity to recognize them as valid text files.

If we add the file "granular.txt" containing the RTcmix code above to our Unity assets, we can edit it the same way we edit C# scripts that work as assets in Unity. To access the RTcmix code in the file in our game object script, you can take advantage of the Unity/C# "TextAsset" class.

Essentially, you declare a public variable that will 'hold' your TextAsset scorefile, and you can then extract a string from that TextAsset for use by the RTcmix.SendScore() method. Here is how to set it up:

After this setup, the granscore variable (which is a 'global' variable in the class because -- like with the int objno = 0; etc. global variables -- we declared it at the top of the class definition, outside any class methods) is the RTcmix scorefile string that you can send for parsing/execution in the appropriate place in your code: The only trickiness is to recognize that by declaring public TextAsset grantextfile; at the top of the class definition, it exposes a slot in the Unity inspector of the associated game object for that grantextfile variable. You need to drag the "granular.txt" file from your Assets into the slot so that the public grantextfile variable will reference the "granular.txt" file with the RTcmix code in it.

alter a beep

RTcmix has two different ways for allowing data from Unity to change the parameters of a sound being synthesized or processed. One way is to change parameters of an executing RTcmix instrument dynamically while it is making sound. RTcmix has 'special' parameters for all of it's synthesis/signal-processing instruments called "PFields" that allow you to do this. These can be addressed from within Unity. We will alter the non-repeatig 'beep' script to show this.

In the 'beep' class, we will use another variable, frequency, declared globally (at the top of the class definition) to set the frequency of the repeating WAVETABLE() RTcmix instrument. Our setup now looks like this:

We set an initial value (700.0f) for the frequency variable in our Start() method. It corresponds to the "700.0" that was set as the default value in the RTcmix makeconnection() scorefile command. We're setting frequency as a 'float' variable, but it could be cast as a 'double' or an 'int'. RTcmix will accept them all.

The WAVETABLE() is started with a duration of "99999" -- this is just to insure that the note continues to play so that we may alter the frequency when we want. That value is arbitrary, and if 99999 seconds is too short it can be extended.

Next we add script code to the "beep" class definition to alter the value of the frequency variable. We do this in our Update() method by seeing if the user has typed an Up or Down arrow:

If the Up arrow is pushed, 10.0 will be added to the value of frequency. The Down arrow will subtract 10.0 Hz. The modified value is then sent to the executing WAVETABLE() instrument via the RTcmix.setpfieldRTcmix (1, frequency, objno); method. The "1" is the inlet number, set by the makeconnection() command in the RTcmix score.

This will work, but it's not the most efficient way of doing the task. The Update() method will be called at the frame rate of Unity, usually 60 times/second. We only need to update our WAVETABLE() frequency value when the user presses one of the arrow keys -- probably not 60 times/second. A better approach would be this:

which would only call the RTcmix.setpfieldRTcmix() method when a key was pressed.

modifying RTcmix scorefiles

RTcmix scores themselves can also be altered dynamically to open up another possibility for interactively sending data from Unity into RTcmix. Sscorefile variable values can be reassigned before the score is sent to RTcmix. The "rtcmixmain.cs" file contains a utility function to accomplish this.

To take advantage of this capability, the RTcmix score needs to include special variables with a"$" as the first character and a number as the second (this is also from the [rtcmix~] object in Max/MSP). The "$" signals that this variable needs to have a value assigned from "outside" RTcmix, and the number indicates the ordering of the assignments.

For example, the small RTcmix score:

will expect that the value for the amplitude parameter ($1) and the frequency parameter ($2) will be set from Unity values "outside" RTcmix. The utility function setscorevalsRTcmix() included in the "rtcmixmain.cs" file does this by taking a score string with the $variables embedded within and returning a score string with substitutions made.

Let's look at a modified version of the RTcmix code in the "granular.txt" example from above to show how these $variables work:

The values for the hifreq and lowfreq variables can be set using the setscorevalsRTcmix() utility function. This function takes a score string with $variables and substitutes them with values from a list of parameters passed with the function. It then returns a string with the values set for RTcmix to parse and execute.

If we took the granular synthesis score above with the $variables set for hifreq and lowfreq and put it in our "granular.txt" file, we can do this substitution with the following code:

This $variable substitution gives us another opening for transferring values from Unity into RTcmix. If we use the recurring MAXBANG() scheme for re-triggering the score, we can set new values for the $variables every time the score is passed into RTcmix. The following code shows how to do this, using the Up and Down arrow keys to modify the value sent for $1 (hifreq) and the Right and Left arrow keys setting the value for $2 (lowfreq):
    using UnityEngine;
    using System.Collections;
    using System;
    public class beep : MonoBehaviour {
    	int objno = 0;
    	rtcmixmain RTcmix;
    	public TextAsset grantextfile;
    	float hifreqval, lowfreqval;
    	String granscore, granscore2;
    	// Use this for initialization
    	void Start () {
    		RTcmix = GameObject.Find ("RTcmixmain").GetComponent<rtcmixmain>();
    		 RTcmix.initRTcmix (objno);
    		granscore = grantextfile.text;
    		// set default values for "hifreqval" and "lowfreqval"
    		hifreqval = 900.0f;
    		lowfreqval = 500.0f;
    		granscore2 = RTcmix.setscorevalsRTcmix (granscore, hifreqval, lowfreqval);
    		RTcmix.SendScore (granscore2, objno);
    	// Update is called once per frame
    	void Update () {
    		if (Input.GetKey (KeyCode.UpArrow)) {
    			hifreqval = hifreqval + 10.0f;
    		if (Input.GetKey (KeyCode.DownArrow)) {
    			hifreqval = hifreqval - 10.0f;
    		if (Input.GetKey (KeyCode.RightArrow)) {
    			lowfreqval = lowfreqval + 10.0f;
    		if (Input.GetKey (KeyCode.LeftArrow)) {
    			lowfreqval = lowfreqval - 10.0f;
    	void OnAudioFilterRead(float[] data, int channels) {
    		RTcmix.runRTcmix (data, objno, 0);
    		if (RTcmix.checkbangRTcmix (objno) == 1) {
    			granscore2 = RTcmix.setscorevalsRTcmix (granscore, hifreqval, lowfreqval);
    			RTcmix.SendScore (granscore2, objno);
    	void OnApplicationQuit() {
    		RTcmix.destroy (objno);
Be aware that depending on how often a new score is sent to RTcmix, a latency between setting the values in Unity and having them take effect in RTcmix will occur.