DIY Time part 2: Click to Clock & Nitrotracker

For a period of time in around 2007/2008, before the iphone got fully into its stride, the Nintendo DS was the platform for portable music apps. I bought a DS Lite specifically to take to work and make tunes in my lunch break (a 24 year old with a kid’s game console, although not ‘cool’, was just about socially acceptable at the time). Synth giant Korg even got involved in the scene with their DS-10: an excellent handheld recreation of the MS-20. However, the pick of the software for me was Nitrotracker, written by a German coder called Tobias Weyand and distributed for free.

So what is Nitrotracker? It’s a sample-based tracker that takes its cues from Fasttracker II – in other words, an old-school music sequencer. On classic trackers the note entry was done via your computer keyboard: here you use a stylus and a mini piano keyboard on the DS’s touchscreen. Believe me, once you are used to it, the workflow is insanely fast.

Here’s the kind of thing I could knock up in a lunchbreak:

The main problem that I encountered was how to integrate my Nitrotracker compositions with the rest of my studio. First off, when the tempo marker in Nitrotracker reads “140”, this doesn’t necessarily equal 140 beats-per-minute. So if I recorded some nice blippy patterns from Nitrotracker into my computer, and wanted to add a drum machine over the top…..well, let’s say it was more ‘miss’ than ‘hit’.

I tried several solutions to this problem. First off- the vaunted MIDI functionality of Nitrotracker itself. I bought a DSerial interface, but found the latency to be too high for drum hits, and experienced a lot of stuck notes. Then I tried an audio-to-MIDI clock converter in the form of the RedSound Soundbite Micro. This was better, but my propensity for wiggy arrangements meant that it often dropped the beat. Bottom line – the Soundbite is a good unit if you have a solid 4/4 kick drum. The solution only presented itself much later, when I came into possession of a Korg Volca Keys.

The Volca range have 3.5mm ‘sync’ inputs and outputs. The specs from Korg state that these send and receive a 5V clock pulse- the sort of voltage-based signal usually associated with analogue sequencers and modular equipment (of which I have none). However, Korg also promote an app called “SyncKontrol“. Here’s where it gets interesting (no, really!)….

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The SyncKontrol app runs on any iOS device, so iphone, ipad etc, all of which have a standard stereo 3.5mm headphone jack, but nothing in the way of CV/Gate outs. I concluded that the sync input threshold of the Volcas must be low enough that an audio signal could trigger them. I downloaded the (free) app, and recorded about 30 seconds of the signal from the headphone output of my ipad into my computer*. I saved a single ‘pulse’ from the resulting recording, and imported the WAV file into Nitrotracker. Here it is:

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Next up, I created a pattern which played back the pulse at a rate of 8 notes per ‘bar’. If you want to get technical, the Volcas sync to 2ppqn, or “2 pulses per quarter note”. On connecting the headphone output from my DS to the Volca, the tempo knob started flashing. Sync was established. But how to get music and sync from the DS simultaneously?

The solution was simpler than I thought- split the signal coming from the DS (I’m working on a custom cable for this, but in the meantime a £1 headphone splitter does the job).

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Next, I hard-panned the sync pulse to one side of the stereo mix, and everything else to the other side. I ended up with a mono signal from Nitrotracker, which I found to be a decent compromise for two reasons; 1) the panning in Nitrotracker is pretty rudimentary anyway- no automation or anything, so not much to miss. 2) mono output means it’s easier to patch it through fun guitar effects like distortion, phasers etc.

So the Volca is synced to the DS, but it doesn’t end there. Korg have been generous in making the Volcas extremely easy to hack– so I added a MIDI output (god, more MIDI???), in a quick-and-dirty fashion:

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The Volca Keys will now happily pump out midi clock in time with the incoming clock from Nitrotracker. Party time!

Here’s the first test, with the sync pulse audible at the beginning for reference. Not the finished article musically, but you get the idea:

OK- so not that many people will have a burning desire to plumb a discontinued Nintendo handheld running homebrew software into a musical environment! However, the Volca element has some excellent mileage in terms of live performance. You could record backing tracks to one side of a stereo mix, with a sync pulse on the other side, and gig with an mp3 player, a Volca or two plus MIDI equipment and keep it all locked rigidly in tempo. In this article, Dan Deacon describes a similar set up, but simply sends his click track to a drummer of the human variety. It’s not only the Volcas that do this- the new Teenage Engineering PO series also have 3.5mm sync inputs. And if you’ve got an expensive modular synth to play with, I’m sure the applications are infinite!

Finally, I’m aware that this is not exactly new technology- we can trace the technique back to 1977 when an engineer called Robbie Wedel synced a tape machine to a modular Moog. The result?

*If you don’t own an iOS device, IN THEORY you could connect the sync output of your Volca to a mixer and record the output as audio: UPDATE 03/03/15 – I have since tested this out and the volume was fine into a standard line input.

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7 thoughts on “DIY Time part 2: Click to Clock & Nitrotracker

    • Good idea, I’ve made the original demo downloadable, so you could use the first few seconds of that until I have time to upload a recording of the sync pulse alone. I think a plain square wave could work too!

      • Thanks… well the square wave does work, but what I wanted to do is create a hardware version of the app using an Arduino (just as an exercise) and add the additional features like swing and play/pause that the app offers. I did try for about only an hour, the tempo worked, but I couldn’t make it swing, and since I don’t have access to an iPhone to reverse engineer the pulses and couldn’t find samples on the net, I gave up, so I think it would be useful for other people in similar situations.

  1. Great writeup, thank you very much for this! Since the existing MIDI support in NT is a bit flakey (as you mentioned) this seems to be a very stable approach to syncing NT with other gear!

    – Tobias

  2. Thanks for the help! some old drum machines can also output 5v pulse signals. So I’m trying to setup my Roland TR626 as a clock divider to a Volca keys, because the 5v is assignable from the rimshot. Also I think (don’t own one) the DR110 outputs 5v sync, which allows you to add it to a midi setup through a Volca.

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