Receiving MIDI Time Codes over USB with the Teensy

Due to a request of a reader of my blog, I elaborated on my extensions for the Teensy 3.x usb_midi library by adding support for callback functions to receive MIDI Time Code (MTC) messages. To fully understand the code, I recommend also reading my post for generating the MTC.

Briefly, the library files where we need to add the missing functions are located (on Mac OS X) in Contents/Java/hardware/teensy/avr/cores/teensy3/. This folder can be found by right-clicking on your Arduino application and then selecting Show Package Contents from the drop down menu.

You can either download the modified files from my GitHub repository and copy them to above folder, or you can modify the files yourself by following the following simple instructions:

Open usb_midi.h and search for "#ifdef __cplusplus". Add the following code one line above that:

Now search for "private:" and add this code right before it:

You are almost done. Save and close the file, and open usb_midi.c instead. Search for "// Maximum number of transmit packets to ..." and add this line above:

As a last step, search for "return 0; } #endif // F_CPU" (they might be distributed over multiple lines) and add these lines of code before the "return 0;"

And voilá, you can now receive MTC messages over USB and evaluate them with callback functions.
Your callback function will receive the MTC as a word parameter. An example sketch showing how to do the decoding is included in the repository...

Monotribe fun

Opinions about the Monotribe are quite controversial. While many like the sound this little device can produce, its lack of midi, 2nd oscillator, etc, are considered a huge draw back by others. Flanked by the Monotron series on the low budget end and with the Volca series having more functionality, the Monotribe appears obsolete and can be tough to integrate into your workflow. However, I got an offer for one that I could not decline - and I love the little thing. Its sound is (except being prone for clicks on note on and off events) raw analog and rich, while not missing a certain level of aggressiveness either.

Further, many of the points of criticism can be readily addressed by slight hardware modifications. These are largely facilitated by labelled soldering pads that Korg graciously put on the pcb. In addition, Midi functionality can be added without the necessity of physically changing the Monotribe, by using a serial connector present in the device and by using Midi commands and messages that are already integrated in all the official firmware releases. Consequently, several commercially available Midi kits from third-parties are at hand, however, these are often overpriced, considering only costs for materials, and many modifications can be implemented with only few and simple steps for a fraction of the price of a kit.

In this context, a modification scene has formed around the Monotribe with a plethora of mods being well described and published online. This information is often dispersed among several sources and I will summarise some of them here while implementing them in my own Monotribe,

Since I would like to have both, Midi DIN connections as well as over USB, I decided to use the Teensy microprocessor again to manage all communication and serve as a bridge between Monotribe, DIN and USB. This approach has also the advantage that there will be quite some processing power available for additional modifications of the synthesizer...

My first implementation is quite crude and demonstrates only basic capabilities: while the Teensy already takes care of the USB Midi communication I further added a small OLED display and a joystick. The display, so far, shows which note is currently played, either through Midi or on the Monotribe's ribbon keyboard, indicates the active drum sounds with icons (not shown in the picture), and visualises the position of the joystick - which in turn controlles LFO frequency and range.

Control Playback/Recording in Avid Pro Tools with an Arduino or Teensy

I would like my Ghz Warrior to be able to sync with Pro Tools. The way I envision this feature, is to be as little as possible in touch with the computer. So instead of using Pro Tools as a Master, and slave the sequencer to it, I would like the Ghz Warrior to be the Master clock and the computer coordinates with that. Since USB hubs are cheap while MIDI DIN hubs are expensive, this should be accomplished through MIDI over USB.

While Pro Tools can send MIDI Real Time Messages (MIDI Clock) and MIDI Time Code (MTC) messages, it can only receive the latter. A quick look at the MIDI reference sheets, and the wikipedia page for better readability, reveals that a full MTC consists of two so-called frames. The combination of both frames encodes the actual second, minute and hour of the song/video/you-name-it that is playing, as well as 2 bits to communicate how many frames will actually be sent per second (FPS). This information is split into eight quarter frames (how was ONE frame defined in the first place?), each consisting of the status byte 0xF1, a zero bit, and then 7 bits encoding the described information in the following way:

  #    Data Byte    Description

  0    0000 ffff    Frame number lsbits

  1    0001 000f    Frame number msbit

  2    0010 ssss    Second lsbits

  3    0011 00ss    Second msbits

  4    0100 mmmm    Minute lsbits

  5    0101 00mm    Minute msbits

  6    0110 hhhh    Hour lsbits

  7    0111 0rrh    Rate and hour msbit

The Digital Warrior, and therefore my Ghz Warrior, is built on the Teensy platform, and I am actually truly grateful to Paul Stofregen and Robin Coon for this great system. In particular MIDI functionalities are extremely easy to implement, and a library for MIDI over USB comes with the installer that well integrates the system into the Arduino IDE. Unfortunately, what is missing in that library are routines to send MTC messages (and Real Time Messages, but more about that in another post).

I quickly wrote two routines to implement sending MTC with the library. To use that functionality on your Teensy board, copy paste the following lines to the usb_midi.h file of the midi_usb library:

On Mac OSX and for the Teensy 3.x boards, you will find the usb_midi.h file by right-clicking on your Arduino application and then selecting Show Package Contents from the drop down menu. In the now opening folder structure, usb_midi.h is located in Contents/Java/hardware/teensy/avr/cores/teensy3/

For the Teensy 2.x platforms, the file is in Contents/Java/hardware/teensy/avr/cores/usb:midi/
Make sure to select the right folder according to the hardware you have (selected in the Arduino IDE).

A fully modified version of the file for the Teensy 3.x is also available on my GitHub page. Further, I have put there an example sketch that synchronises your board with Pro Tools (Arduino/Teensy = Master, Pro Tools = Slave) and have the play/record status of Pro Tools respond to button presses. As a bonus, the option to use a standard serial connection without the need to use above library tweaks are included. By that you can also sync out-of-the-box Arduinos with Pro Tools.

Presets in the examples are a button connected to pin 4, and MTCs with 25 FPS.
For this, in Pro Tools, go to Setup/Peripherals... and set the MTC Reader Port under Synchronization to any:

Then, open Setup/Session and select 25 as the Timecode Rate:

Finally, put Pro Tools online by activating the corresponding button in the Transport window:

When you compile the sketch for the Teensy, make sure to select USB Type: "MIDI" in the Tools menu of the IDE, and everything should work out of the box.



Note:

If you use an Arduino, or compile the Teensy with the USB Type: "Serial" option, you will need to use a serial to midi bridge. This converts the incoming serial commands to actual MIDI messages in your computer. I found the free Hairless quite useful for this.

In Hairless, select your Arduino/Teensy in the Serial Port section, and the IAC Driver as a MIDI Out. Activate the Bridge and you are also done on this route :)

Digital Warrior - SD Card Mod

The parts for my very own Digital Warriors have arrived - and they really look good.

However, as pointed out in my last post, there were a few things I was missing among the functionality:

The Digital Warriors are based on the Teensy microcontroller development system, and consequently, the original design makes use of the Teensy's internal 2kb EEPROM to store its data. Naturally this tremendously limits the amount of data that can be saved.

To be able to use the Digital Warrior most flexibly and efficiently as a stand-alone sequencer, I wanted to use an SD card instead of the EEPROM. This would allow me to implement longer

Unfortunately all through-hole pins on the Teensy are already used by the Digital Warrior's standard functions. To make things worse, we can not freely choose any pins for the SD card access. SD cards are typically connected through the SPI ports and these are on: pin 13 - SCK, pin 11 - MOSI, pin 12 - MISO. Alternatively also pins 14, 7 and 8 can be used respectively, but these are also occupied. The fourth SPI pin, SS, is less of a problem as it is freely assignable.

Looking at the Digital Warrior firmware, it it quickly became clear that the necessary pins are easily re-routable. Pin 11 is used by one of the encoder push buttons, pin 12 the sequencer button, and pin 13 the track button. Changing the pin assignments in the software is pretty easy, rerouting them in hardware is also not really a problem. I decided to use the pads, on the bottom of the Teensy, 31, 32 and 33 for the button pin reroutings and soldered small cables on them before attaching the Teensy to the PCB:

Then I removed the corresponding pins from the headers which I used to solder the Teensy to the pcb. And finally connected the cables to the corresponding spots on the board:

A quick test with my updated firmware confirmed that everything was working well.


Similarly, for the SD card, I decided to use pad 29 for the SS pin, and added a small cable here as well:

Afterwards I soldered the Teensy to the PCB and connect the remaining cables (the purple one was too much) to pins 11 (brown), 12 (red), 13 (grey) as well as GND (black) and 3.3V (white). The other side got soldered to the corresponding points on the micro SD adapter  as described here, and voilà - done:

The first version of the Ghz Warrior firmware to start using the SD card instead of the EEPROM can be found on my GitHub page.

Ghz Warrior

Judging by YouTube videos and his homepage, I really liked the Digital Warrior of Tomash Ghz.
It seemed small, elegant, licensed under CC BY-SA 4.0 - and by that fully tweakable :)
I considered the last point to be particularly important, since I was missing some features for the purpose I had in mind: a fully autonomous sequencer for my synthesisers.

However, at one point when I was on Tomash' homepage to admire the smart device, I noticed that he was calling for preorders of the final batch. Confirming that this was my last chance to get one of little things, I did not hesitate to order the necessary parts for two of the standalone sequencer versions of the Digital Warrior.

Since then I am in very nice and fruitful contact with him, and since he wants to focus on other projects now, decided to also work a bit on the Digital Warrior as a standalone sequencer.
In honour for the great foundation I can built upon, I will call my modified firmware  Ghz Warrior...

The Roisterer - The Beginning

So, I am into DIY synthesisers lately.

What I am missing in my setup is a small effects machine. Something that I can use to simulate (almost) everything from ocean waves, over vehicle sounds, to not-from-this-world sound effects.

Of course it should be controllable by MIDI, but also have an independent interface that is very suitable for live acts. Like some potentiometers and a touch screen to change parameters on the fly like panning, filter cutoff, etc.

Perfectly, it would also have a small footprint on my desk and (now I am pushing it) fit well optically to my other gear.

Most of my own developments so far have been with the Arduino platform, so that was the natural choice. However, for a complex endeavour like this, I have made the experience that a lot of time is typically spent on the generation of the sounds itself, writing the gui, etc.
While I have often enjoyed this in the past, this time I wanted to have something that I can use fast.

I also had a Raspberry Pi still laying around my place, and by this the idea of the Roisterer was born...

Hello World

Hello world,

I consider myself a maker and as such, I have pursued several projects in the past, ranging from home automation, hacked IR remote controls, fire simulations for christmas cribs, etc

Lately, I am mostly interested in building electronic music instruments and I felt that there is a part missing if I do not communicate...

...what I am currently assembling.
...what I am designing and constructing myself.
...which modifications I have added to the work of friends.
...and of course also what music I make with the devices I have built.

So here I am. This blog will mainly focus on the technical details of my work so that my projects can be freely reproduced. Consequently, my hardware developments are published under the CC BY-SA 4.0 license unless indicated otherwise. The software is of course open source and the particular licensing scheme will be highlighted in the corresponding files as published on my GitHub page. Some aspects of my work will be communicated free of all technical details through my Facebook page. And the music I intend to produce with all the DIY gear will be made available on my SoundCloud page.


, Karg