Monthly Archives: May 2015

Korg Triton Taktile: Snap Review

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The Korg Triton Taktile has a double personality. On one hand, the Triton Taktile (TT) is a MIDI controller with eight knobs, eight sliders, eight buttons, sixteen pads and a set of DAW function buttons. (These are the specs for the 49-key model, the model that I’m using.) On the other hand, it is a synthesizer with the Korg Triton classic sound engine. Right now, I’m playing the TT as a synth and I will be concentrating on the synth features.

The Sound On Sound review of the Korg Taktile controller (the model without the sound engine) is very well-written and I recommend reading the SoS article for more information about the TT’s control capabilities. I will say that Korg hit my major checkmarks for a controller: a 49-key keyboard with a good action, expression pedal input, sustain pedal input, and TA-DA, a 5-pin MIDI output in addition to the USB-B connector for power and computer/tablet communications. The TT will operate on a portable, rechargeable USB power pack (minimum 5V 1A output) and that is in fact how I’m using it in the studio. The picture below shows the Triton Taktile under battery power. The TT weighs just a little bit over 8 pounds (3.8kg) and is easy on the eyes as well as the back.

TT_with_battery

The TT connects to either headphones or external amp through a 3.5mm stereo jack. All of the connections are made through a panel on the right side of the TT. The output level is sufficient for comfortable listening on Roland RH-A7 headphones, my current choice for head gear.

As you might be aware already, you don’t get a full Triton classic. The TT is not multi-timbral and it does not have combinations (“combis” or layers) and insert effects. However, you can bring up one of 512 classic programs (voices) and play your heart out! There are two system-level master effects (MFX1 and MFX2) that are appropriate for the preset voice, e.g., chorus and reverb on electric piano. The TT is strictly a preset machine as program edits cannot be stored. This hasn’t cramped my act so far, but like any of the TT’s limitations, it could be a deal-breaker. You can save your favorite preset programs into two sets of favorites (set A and set B, each set with eight slots) for quick patch selection.

Hit the dedicated SOUND button to leave controller mode and go to synth mode. The current patch number and name are shown on the nice bright OLED display. Even though the OLED display is small, it is very readable. There are three ways to select a program:

  1. Press one of the program category buttons (assignable buttons F1 to F8). The TT selects the first program in the category or the last selected program in the category. It remembers the last selected program until power-off.
  2. Use the value slider (ribbon) to scroll through the programs. Tap the “+” or “-” at either end of the slider to increment/decrement, or slide your finger along the ribbon to move quickly to a new patch.
  3. Select one of your favorite programs from either set A or set B.

It takes a little practice to get the hang of the slider. Do not take this ax to a gig and expect to select patches on the fly! I recommend setting up favorites and getting the general layout of the patches before hand. Otherwise, an embarrassing epic fail will ensue.

The keyboard feels very good for a controller in this price range. It has a little more resistance than the Yamaha MOX series, for example. I find it quite comfortable to play — it does not feel like a toy. Korg claim that it is the same action as the Krome and I have no reason to doubt them. The pitch bend and modulation wheel also have a satisfying feel. The knobs and sliders are a little bit “light” to me. I don’t have an opinion on the pads as yet.

I enjoy playing this instrument! The knobs and sliders control eight parameters: volume, cutoff, resonance, attack, delay, release, MFX1 and MFX2. Cranking the cutoff and resonance is a real visceral thrill. The two master effects, unfortunately, are very subtle and understated. The TT cries out for a multi-effects unit with distortion and other sonic manglers.

My favorite sounds are the electric pianos, drawbar organs, church organs (!), strings, and acoustic guitar. Korg strings have always had a wonderfully expressive depth and these patches do not disappoint. The electric pianos are very clean. I threw a cheap Danelectro overdrive on the output in order to realize the EP’s full funked-up potential. Oh, for a multi-effects unit, Korg!

The brass isn’t too bad, especially the horns, cornet and flugelhorn. The TT’s woodwinds are pretty naff — yuck. My musical personality is split between liturgical church music and jazz/funk/60s rock. On the church side, I’m disappointed with the oboe, clarinet and other reeds. On the pop side, I don’t often venture into synth territory. However, the HipHopLead patch is great when you feel the urge for Herbie. There are a lot of lead and pad sounds to explore and I’m sure that I’ll find a few other useful patches.

The handbook in the box is helpful, but not sufficient. Be sure to download the parameter guide and the Triton Taktile-specific MIDI implementation chart. Korg could be a little more forthcoming about the MIDI implementation considering that the Taktile series are MIDI controllers for heaven’s sake. The full list of programs is at the absolute end of the parameter guide. I always look through the list of patches for a synth/workstation when considering a purchase and this list is somewhat hidden away at the end of the parameter guide.

Bottom line, I’m happy with the Triton Taktile even when its limitations are taken into consideration. It could be the heart of a light-weight, portable, battery-powered rig and I’m exploring that potential right now.

Polyphonic Arduino synthesizer

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If you’re interested in building an Arduino-based ROM-pler, this next project is for you!

One of my long term dreams is to build a low-cost 60s-style combo organ. My latest project uses an Arduino UNO as a sample playback, sound synthesis engine. Although the waveforms are taken from the old VOX Continental and Farfisa Mini Compact organs, the design and code could easily use single cycle waveforms from a vintage synth, a string machine, your first born child, whatever! The 60s combo organ project is essentially a software ROM-pler that plays back up to five waveforms at a 22,050Hz sampling rate.

The project hardware consists of an Arduino UNO and a Narbotic Instruments MidiVOX shield. The MidiVOX shield has a Microchip Technologies MCP4921 12-bit digital to analog converter (DAC) and an opto-isolated MIDI input. Although the MidiVOX is no longer in production, it’s basic circuitry is easy to recreate; several other popular audio shields use the MCP4921.

Waveforms are stored in the Arduino’s program memory (PROGMEM), just like code. Program memory is non-volatile and the waveforms are ready to go just like a pre-loaded sketch. The combo organ sketch sets up TIMER1 to generate interrupts at a 22,050Hz sample playback rate. The interrupt handler reads the next sample for each of five virtual tone generators, sums the samples together, and writes the next aggregate sample to the DAC.

MIDI communication is performed through the standard Arduino MIDI library (version 4.2). The sketch registers two callback functions via the library: a note ON handler and a note OFF handler. The MIDI note handlers configure the five virtual tone generators. The sketch’s loop() function is trivial — it merely calls the MIDI library read() function and checks a reset button on the MidiVOX shield.

We all know that Direct Digital Synthesis (DDS) — the usual approach for sample playback — is a compute intensive technique for sound synthesis. DDS dynamically shifts the pitch of a stored waveform from its root pitch (the frequency of the sampled note) to the target pitch (the frequency of the MIDI note played by the musician). DDS performs waveform pitch-shifting through phase accumulation and interpolation. Floating point arithmetic is too slow and most DDS implementations use fixed point arithmetic. Even then, the computational load is heavy.

So, how did I achieve five note polyphony? Instead of storing a single waveform at a single root pitch, my approach stores twelve waveforms — one waveform for each basic pitch in the chromatic scale. The algorithm uses integer phase increments, thereby eliminating floating or fixed point arithmetic and interpolation entirely. The approach requires more space, but is quite fast. Each sampled instrument occupies 20% of program memory, allowing up to four different instruments before running out of PROGMEM.

Here are two quick MP3 demo files: a Farfisa-type sound and a and a VOX-type sound. I created the vibrato by routing the audio signal through an inexpensive Behringer UV300 vibrato pedal.

As usual, we always publish code. Need a cheap ROM-pler? Now you’ve got one!

Update 22 July 2016: If you’re into retro, be sure to check out the Arduino lo-fi beat box project. Filled with lo-fi TR-808 goodness!

MidiVOX: An appreciation and review

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They just don’t make ’em like they used to. In the case, of the Narbotic Instruments MidiVOX shield for Arduino, I really mean it!

The MidiVox is a bit of a blast from the past as Narbotic no longer manufacture and sell the MidiVOX shield kit. Major bummer. Luckily, I purchased one of these little gems from the MakerShed when the shields were available a few years ago. Narbotic kindly maintain the design information and code on their Web site.

To me, the MidiVox is a most logical combination of a MIDI IN port and a 12-bit digital-to-analog converter (DAC). The MIDI port incorporates a 6N138 optocoupler for electrical isolation and a 5-pin DIN connector. The port is connected through a “PGM/MIDI” switch to Arduino digital pin D0, also known as the serial receive (RX) pin. The PGM position connects the serial pin the usual way in order to download to the Arduino. The MIDI position connects the Arduino serial RX pin to the MIDI IN circuitry. The switch component is robust and is easily accessible when the MidiVOX is on top of the Arduino and/or other shields.

The 12-bit DAC is a Microchip Technology MCP4921. This DAC is used in several other audio shield designs including the Adafruit Wave Shield and the Nootropic Design Audio Hacker Kit. The MCP4921 connects to the Arduino SPI port through digital pins D13 (SCK), D11 (MOSI), and D9 (chip select/slave select). Conventional practice recommends using D10 as slave select (SS), but it isn’t a big deal to use D9 instead as this is mainly a software issue. Slave Select (called “chip select” in the MCP4921) chooses and enables communication with the slave device. This capability is essential when more than one device is connected to the same SPI interface as in the case of the Nootropic Audio Hacker shield.

Although it seems like a no-brainer to connect all SPI devices to the Arduino SPI pins, the Adafruit Wave Shield does not follow this approach. It connects the SD card interface to the SPI pins, but connects its MCP4921 to three ordinary digital pins. The Wave shield software bit-bangs the digital pins to transfer data to its DAC. I’m not a fan of this approach, preferring to use standard libraries instead of possibly buggy, poorly documented bit twiddling code.

The MidiVOX shield implements a 2-stage, passive filter following the DAC output. The MidiVOX sends a mono signal through an on-board trim pot into a 3.5mm audio output jack. Trim pots are usually rated for a relatively small number of operating cycles, so it’s best to set this level once and make volume adjusts at an external mixer, preamp, or whatever.

The MidiVOX shield provides a DATA LED controlled by digital pin D7. The shield also has a RESET button (momentary contact switch) connected to digital pin D6. This button is ACTIVE LOW, meaning that the button pulls D6 to ground when it is pressed. Therefore, the pin mode should be configured as INPUT_PULLUP such that D6 is pulled up internally when the button is not pressed (i.e., the momentary contact switch is open).

Construction was easy. The resistors have five color bands, but don’t let this throw you off. The construction directions give the correct color code and you can (and should!) always check resistor values with a meter before insertion and soldering. I replaced the basic header pins with “stackable headers” (two 8-pin and two 6-pin). Stackable headers provide a way to make easy external connections to the shield stack from a breadboard, etc.

The completed board is shown in the photo below. The MidiVOX is stacked on an Arduino UNO with the USB, audio and MIDI cables, and is ready to go.

MidiVox

I wrote a diagnostic sketch to check out the different parts of the MidiVOX. I wish manufacturers would provide check-out sketches instead of relying on somebody’s possibly flaky application sketch for smoke testing. If something is busted, it’s important to find it early through a directed test that isolates the failure. Fortunately, everything checked out OK the first time!

The MidiVOX diagnostic program is an Arduino sketch to check out parts of a Narbotic Instruments MidiVOX shield. Rename the “loop” functions and rebuild in order to test a particular section of the shield.

Since the MidiVOX is discontinued, we’re all out of luck if we want to get (another) one. However, I strongly recommend studying the MidiVOX design. When I first got started with Arduino and MIDI, I borrowed the MIDI IN circuitry and the low pass filter design. These are simple, solid circuits and are good basic building blocks for other designs and applications.

Where to next? My dream is to build a low-cost 60s combo organ with the era-appropriate look and sound. The organ would look like a Vox Continental with a Z-shaped chrome stand and bright red Tolex covering. It would sound like either a Farfisa or a Vox — nothing too nuanced with all of the drawbars or tabs turned on. I’d like to use a cheap and lightweight MIDI controller as the keyboard. The controller would drive a low-cost (Arduino-based?) sound generator. I’m hacking out a prototype using an Arduino UNO and the MidiVOX shield. More to come…