New Yamaha workstation at NAMM 2016?

True gearheads are already making predictions and plans for 2016 Winter NAMM, January 21-24, 2016. Winter NAMM rumors abound including “Montage,” the rumored name for the rumored new Yamaha synthesizer workstation.

See the list of new waveforms in the Montage and read my initial review of the Montage8. Update: May 10, 2016.

Find the latest links, pictures, rumors and facts here . Update: January 21, 2016.

Check out some new thoughts about the rumored workstation and preliminary comments . Update: January 18, 2016.

Many folks — myself included — anticipate the release of a new Yamaha synthesizer workstation at the next NAMM. Much has been made of the registered trademark “Montage.” I don’t really care too much about what they call it, as I care about what it will do.

Last month, I posted two articles about the new Yamaha tone generation chip called “SWP70”:

This chip made its first appearance in the new PSR-S770 and PSR-S970 arranger workstations. Lest anyone scoff, the S770 and S970 produce Motif-caliber sounds including the REAL DISTORTION effects added to the Motif XF by the v1.5 update. The previous tone generator (SWP51L) is used throughout the mid- and upper-range Yamaha keyboard products including Clavinova, MOX/MOXF, Motif XS/XF, and Tyros 4/5. The number of tone generator chips varies by product specification and, most notably, sets the maximum available polyphony. A new tone generator chip is a pretty big deal since it will have an impact on all mid- and high-grade electronic instruments across product lines.

My earlier article about the SWP70 is written from the perspective of a computer architect and is way too nerdy for normal people. 🙂 Let me break it down.

Musicians using VST plug-ins within a PC-based DAW are familiar with the concept of sample streaming. In the quest for greater realism and articulation, sample libraries have become huge. These libraries simply cannot fit into fast random access memory (RAM) for playback. As a work-around, a software instrument reads samples from a drive-based library on demand and only a small part of the entire library is resident in RAM at any given time. The process is often called “sample streaming” because the software instrument streams in the samples on demand from a large fast secondary memory like a Solid-State Drive (SSD). The Korg Kronos workstation caught everyone’s attention because it incorporates an x86-based software system that streams samples from an SSD. (For Kronos-related articles, look here and here.)

The SWP70 combines streaming with tone generation. It does not, however, use an SSD for storage. Rather, it subsumes the functionality of the SSD. A moment to explain…

An SSD consists of three major subsystems: SATA controller, temporary storage cache (RAM) and one or more NAND flash memory chips. The NAND flash memory chips typically adhere to the Open NAND Flash Interface (ONFI) standard. This allows expansion and standardized configurability. The SATA controller exchanges commands and data with a computer using the SATA bus protocol. The temporary storage cache holds data which is pre-read (cached) from the NAND flash chips. Caching is required because random access read to NAND flash is too slow; sequential paged access is much faster. Data must be prefetched in order to achieve anything like SATA 1 (2 or 3) transfer speed.

The SWP70 subsumes the SSD functionality. It has its own memory controller and has a side memory port to its own RAM for caching samples. The SWP70 reads samples from its ONFI-compatible NAND flash memory bus and stores the samples in its cache. The tone generation circuitry reads the samples from the cache when it needs them. The SWP70 solution is, effectively, sample streaming without the added cost and latency of SATA bus transfers. The samples coming into the SWP70 from flash are compressed, by the way, and the SWP70 decompresses them.

The SWP70 will very likely make an appearance in the new Yamaha synthesizer workstation. The S770 and S970 do not make full use of the SWP70, so we have yet to see what this chip is fully capable of. We can definitely expect:

  • Much larger wave memory (4GBytes minimum)
  • Greater polyphony (256 voices or more)
  • More simultaneous DSP effects (32 units or more)
  • The demise of the expensive expansion flash DIMMs

I would simply love it if the new workstation implemented some form of Super Articulation 2 voices (now supported by Tyros 5). The raw resources are there.

User-installed expansion memory may be a thing of the past. The current DIMMs plug into a two channel, full parallel memory interface. That interface is gone and the SWP70 communicates with flash NAND through an ONFI-compatible interface. The Motif and Tyros follow-ons will likely reserve space for user samples and expansion packs in built-in flash memory just like the new mid-range PSRs.

What does Yamaha intend to do with all of this polyphony? Current high-end models like the Tyros 5 use two tone generation chips. Yamaha could replace both chips with a single SWP70 and pocket the savings.

Another possibility is to provide advanced features for musical composition that combine MIDI and audio phrases. Here is a list of technologies covered by recent Yamaha patents and patent applications:

  • Beat detection and tracking
  • Chord detection
  • Synchronized playback of MIDI and audio
  • Combined audio/MIDI accompaniment (time-stretch and pitch-shift)
  • Object-oriented phrase-based composition on a time-line
  • Accompaniment generation from chord chart
  • Display musical score synchronized with audio accompaniment
  • Phrase analysis and selection (via similarity index)
  • Near ultra-sonic communication of control information
  • Search for rhythm pattern similar to reference pattern

A few of these technologies are covered by more than one patent — recurring themes, if you will. I could imagine a screen-based composition system that combines audio and MIDI phrases which are automatically selected from a database. The phrases are transparently time-stretched and pitch-shifted. Some of the compositional aids may be implemented in the workstation while others are tablet-based. The tablet communicates with the workstation over near ultra-sonic sound (no wires, no Bluetooth, no wi-fi, no time lag).

Sample-based tone generators already perform pitch-shifting. That’s how a single sample is stretched across multiple keys. A musical phrase can be pitch-shifted in the same way. As to time-stretching, stay tuned.

Some of these features, like accompaniment generation from a textual chord chart, are more likely to appear in a future arranger workstation product. Making product-specific predictions is a risky business, especially if you want to get it right!

Yamaha — the business — is keenly interested in growth and expanding markets. Management sees opportunity in growth markets like China. The need to combine audio phrases with MIDI is driven by non-Western music: time signatures other than 3/4 or 4/4, different scales, different playing techniques and articulations. These concerns are perhaps more relevant to the arranger product lines. However, phrase-based composition that manipulates and warps audio and MIDI transparently is a basic feature of many DAWs. (Think “Ableton Live.”)

One final theme seems to recur. Yamaha appear to be interested in analyzing and accompanying non-keyboard instruments. The market for guitar-driven accompaniment is much wider and deeper than today’s arranger workstations and is a lucrative target.

Here are links to a few earlier articles, including speculation about the new Yamaha synthesizer workstation:

These articles link to further background information. Of course, we’ll know a lot more once Winter NAMM 2016 is underway!

All site content Copyright © Paul J. Drongowski unless otherwise indicated.

Clear the decks?

Yamaha have announced a truly stellar promotion to move Motif XF workstations. The Motif XF Fully Loaded expansion pack includes a FireWire expansion board, two FL1024M memory modules and an USB drive filled with content including Chick Corea’s Mark V electric piano. (See the promotions page at the Yamaha web site for additional details.)

Wow! This promotion really caught my attention and if ever there was a time to upgrade to an XF, it’s now.

Of course, this aggressive promotion could also mean that a new synthesizer workstation will be announced in the not-too-distant future. Winter NAMM 2016, perhaps? Old inventory has got to go!

After the Reface surprise, I’ve given up predicting specific product features, especially based upon a (rumored) product name. The word “Reface,” for example, means something completely different to a saxophone player and, yes, Yamaha manufacture saxophones and mouthpieces. 🙂 So, “Montage”, harumph. I am willing to predict, however, that the next high-end workstation will have a new member of the Standard Wave Processor (SWP) family — the hardware chip that underlies the tone generation infrastructure. (See Serial Memory and Tone Generation.) This is big step for Yamaha because the current SWP51L, for example, is used in everything from mid-range arrangers, to MOX/MOXF, to Motif, to Clavinova.

Just taking in the gestalt of Yamaha’s recent patent filings, they have been actively building their portfolio in at least three areas: human vocal processing and synthesis (VOCALOID), music analysis and combined MIDI/audio accompaniment.

VOCALOID has been a commercially successful software product. The tech has, by the way, some similarities to the “connective” capabilities of Articulated Element Modeling (AEM), known more broadly as “Super Articulation 2” on Tyros. VOCALOID requires frequency domain signal processing, so unless Yamaha have knocked down some real computational barriers, VOCALOID will probably remain a non-real time synthesis technique.

“Music analysis” is a broad area and a rather vague term. At a fundamental level, this area includes beat (tempo) detection and scale and harmony (chord) detection. I think we already see some of these results at work in the Yamaha Chord Tracker app. Chord Tracker analyzes an audio song. It detects the tempo and beats, and partitions the song into measures. Chord Tracker identifies the chord on each beat and displays a simplified “fake sheet” for the song. Chord Tracker can send the “fake sheet” to a compatible arranger keyboard for playback.

Music analysis also includes high-level analysis such as extracting the high level characteristics of a piece of music. This kind of analysis could allow a rough categorization and comparison between snippets of music (similarity index). We haven’t seen the fruits of this technology (yet), but one could imagine a tool that suggests an accompaniment based on what the musician plays or based upon an existing musical work. BTW, the word “musician” here includes guitarists, woodwind players, etc. and not just keyboardists. The world-wide market for non-keyboard instruments is bigger than the market for keyboard-based instruments. (Guitars alone outsell keyboards nearly 2 to 1 in the United States.)

The third main area of exploration and filings is combined MIDI/audio accompaniment. Up to this point, Motif arpeggios are MIDI-like phrases, not audio. Arranger workstation styles are MIDI (SMF in a Halloween costume). Neither product works with MIDI and audio phrases in a transparent way like the very successful Ableton Live. Yamaha’s patent filings disclose arpeggio- and/or style-like accompaniment using a mix of MIDI and audio phrases. Audio phrases are warped in time and pitch to match the current tempo and key scale.

Now, let’s throw these technologies into a bag and shake them around. Imagine a compositional assistant that analyzes a piece of music (recorded or played live), determines tempo, beats, chord changes and more, and automatically whips up an accompaniment or track. MIDI and audio phrases are selected from a library based upon a similarity index between the reference track and phrases in the library. If this is Yamaha’s vision, then double wow! The combination of these technologies would raise the level of music composition substantially from it’s tedious, point-and-click existence. It finesses the problem of listening to the phrases in the Motif/MOX arpeggio library, selecting the most applicable phrases and combining them. DigiTech TRIO is already sniffing around this territory.

Naturally, patents do not imply product. Therein lies the danger of making predictions.

Which brings me, finally, to US Patent 8,779,267 (July 15, 2014). If someone can explain this patent to me, thanks. The invention seems to analyze an incoming musical signal (using some heavy DSP), generate almost ultra-sonic (>18KHz) “control tones,” and produce a multi-timbral accompaniment or track. Amazing stuff.

The near ultra-sonic technique is already in use. The AliveCor Mobile ECG monitor uses ultrasonic tones to communicate with iPhone/iPad. The AliveCor doesn’t require power-sucking Bluetooth (and its emissions certification.) The monitor runs on a CR2016 battery. The downside, in the case of AliveCor, is that its monitor pad must be near the mobile device for reliable communication.

All site content is Copyright © Paul J. Drongowski unless otherwise indicated.

Yamaha Reface (No, I haven’t played it)

It’s Internet de rigueur to comment on the new Yamaha Reface keyboards — whether you’ve played them or not! So, here goes…

I’m in fat city with an original AN-200 (Prophet-5 plus beat machine in a box), a P-50m (pianos in a box), a CS-01 (monophonic analog synthesizer) and a Nord Electro 2. Although a few of these pieces are gathering dust, they pretty much cover the sonic territory of Reface. DX-wise, I had more than enough FM in the 80’s, thank you, and could always get my old CE-20 repaired, if the urge to frequency modulate should ever overcome me again. Overall, I’m unlikely to take the plunge and buy a Reface keyboard just out of necessity.

First off, I genuinely wish Yamaha all the success in the world with these products. This is the first time that Yamaha have strayed from the AWM2 mainstream in some years. I would hate to see this innovative product line tank and make Yamaha risk-averse. The Reface product line started out as an after-hours skunk works engineering project. The fact that Yamaha committed to manufacturing and marketing Reface is significant and shows real effort to shift their corporate culture. Further, if Reface makes scads of money for Yamaha, then its profits will lift other boats within Yamaha.

Sonically, Reface sounds pretty darned good. The CP and YC are my favorites because they fit with the musical genres that I work in. I hope that some of this technology will migrate into future synthesizer and arranger workstation products. Spectral Component Modeling (which includes Virtual Circuit Modeling) grew from VL technology. The VCM effects in the MOX/Motif are quite good, so please give me more of that! I am pleased to see Yamaha work on organ emulation and would like to see the drawbar control, vibrato/chorus and rotary speaker effects in a new workstation. Both the Motif/MOX and higher-end arrangers are missing the Hammond “vibrato scanner” effect — a significant omission.

So, why am I not buying? Apparently, “mini” keyboard sales are making money for Novation and others, and Yamaha wants a piece of this market. The decision to use mini-keys strongly bifurcates the marketplace — you either like (accept, tolerate) mini-keys or you don’t. I’m a “don’t.” I have tried mini-keys in the past and, well, no thanks. This is not an “anti-Yamaha” position — I lost all interest in the Korg Odyssey, for example, when I learned that it had mini-keys.

The Reface is touted as a portable, take-it-anywhere keyboard. If you’ve been reading this blog, then you know that I’ve put together a portable rig based on the Korg Triton Taktile (TT.) The TT has 49 full-size keys and is not much bigger or heavier than a Reface. The TT key bed is excellent and four octaves is enough room to roam. Although the TT is missing the up-to-date tone generation and effects technology in Reface, it’s a very playable alternative to Reface.

Finally, there is the issue of the $500 street price. I suspect that Yamaha is looking to make a few extra bucks from the early adopters. Korg may have pursued the same strategy with the TT. They brought the TT out at a higher street price and then eventually reduced the price to the current $350 USD. The TT comes with a superb bundle of software plug-ins and offers, making it a terrific bargain. Unfortunately, for Yamaha, this is the competition facing Reface (pun intended) and a $500 street price looks mighty steep for an ax with mini-keys and no free software incentives.

Internet reaction from Reface detractors has been vehement — far over the top, in my opinion. It seems like some people have taken Reface as a personal affront! Please, settle down. Yamaha is a big company and they will surely roll out new products for the rest of us. The Motif refresh is overdue, for example, and must be in the works. It’s good to see Yamaha releasing new products that are out of its mainstream offerings. All the best!

What’s in a name?

Anything that we want to go from just a beginner to a pro,
You need a montage (montage)
Oh, it takes a montage (montage)
Team America Lyrics

Back in January before Winter NAMM 2015, there was a lot of speculation about a new Yamaha workstation to replace the venerable Motif product line. Yamaha filed for the trademark name “Montage” in December 2014 and many wondered if this would be the name of the new workstation. (Yamaha have a teaser ad for “Reface” at https://www.yamahasynth.com with a countdown clock leading up to Summer 2015 NAMM week. Your guess is as good as mine!)

Getting a little bit Zen for a moment, it doesn’t matter what a thing is called. All that matters is what the thing is.

Periodically, I troll the United States Patent and Trademark Office (USPTO) database for interesting patents and patent applications. Yamaha carefully (and wisely!) protects its inventions through patents. Yamaha R&D, by the way, rarely publishes in the scientific literature, which is another way to stake your ground. Patent protection is stronger legally. A patent costs money, so a corporation is usually serious about a technology when it makes the commitment to file. The Yamaha patent applications cite Japanese applications/patents to establish priority in the United States. Thus, there is usually an existing Japanese application or patent that was filed at an earlier date for each US application.

Of course, a patent does not necessarily indicate that a product will follow. However, I’ve noticed a trend in some (relatively) recent filings by Yamaha.

Let’s start with US Patent Application Publication 2013/0305902, “Accompaniment Data Generating Apparatus,” published November 21, 2013. Quoting the application, “An object of the present invention is to provide an accompaniment data generating apparatus which can generate automatic accompaniment data that uses phrase waveform data including chords.” This rather lengthy patent application describes a musical instrument keyboard that uses audio waveforms in the same way that an arranger or Motif-series workstation uses MIDI phrases (AKA arpeggios). The application cites Japanese Patent Publications No. 2900753 (MIDI-based accompaniment) and No. 4274272 (MIDI-based arpeggio performance) as prior art.

US Patent Application Publication 2013/0047821 (published February 28, 2013) covers similar ground. This application adds waveform pitch shifting and time stretching. It cites Japanese Patent Publication No. 3397082 on the specific capability of pitch shifting and time stretching. Audio phrases (waveforms) need to be transposed via pitch shifting and must fit into the rhythm via time-stretching.

US Patent Application Publication 2013/0305907 (published November 21, 2013) is related to the previous two application. It covers production of chords using audio waveforms, guided by chord root and chord type.

US Patent Application Publication 2014/0033902 (published February 6, 2014) is titled “Technique for Analyzing Rhythm Structure of Music Audio Data.” The technique described in this application identifies the beat positions and intervals in a piece of music in audio form (i.e., rhythm pattern analysis). Figure 1 shows the embodiment (design) of the technique within an accompaniment generation system. The beat position information is used to synchronize playback of both MIDI and audio phrases. The diagram shows a “MIDI reproduction section” and an “Audio reproduction section.”

The most recent publication is 2015/0154979 (June 4, 2015) and is titled “Automated Performance Technology Using Audio Waveform Data.” The application deals with a specific issue that arises when audio waveforms are used for accompaniment (pitch shifting and time stretching). Quoting the application, “it is an object of the present invention to properly deal with a processing delay and sound quality deterioration that are likely to occur when audio waveform data is reproduced with time axis expansion/contraction control performed on the audio waveform data in accordance with a desired performance tempo.”

These are long documents with a lot of detail expressed in excrutiating “patent language.” They are too long and detailed to summarize here. I recommend downloading the patent applications from the USPTO, brewing coffee, and then reading the applications.

Looking at the overall trend, Yamaha are thinking about automated accompaniment that incorporates both MIDI and audio phrases. This technology could be applied to arranger instruments or a new generation of synthesizer workstation. The latest arrangers have “audio styles” which only use audio for the rhythm track. No “harmonic” phrases (e.g., bass line, electric piano comping, etc.) are available. The current Motif generation (the XF and MOXF) have only MIDI-like arpeggios. Possibly, combined audio/MIDI accompaniment was not fully cooked in time for the PSR-S950 and Tyros 5.

I am very interested to see if Yamaha rolls out this technology in future products. The definition of “montage” is “the process or technique of selecting, editing, and piecing together separate sections of film to form a continuous whole.” Hmmm.

Footloose and fancy free

Maybe you would like to play your music in the great outdoors at a family picnic. Or, like me, you would like an extremely light, battery-powered rig for quick set-up at rehearsals.

Modern battery technology to the rescue! More musical instruments and portable speakers than ever run on battery power. Many of these devices sport an integrated rechargeable battery and a USB-based charge or power outlet. You can have that light battery-powered portable rig by combining a battery- or USB-powered keyboard with one of the many available portable speakers.

Here’s how I designed my portable rig.

I started with the KORG TRITON Taktile 49 USB-powered MIDI controller and synthesizer. The TRITON Taktile (TT) has 49 keys and is very light-weight (less than 8.5 pounds). The TT incorporates the Triton Classic sound engine and programs which are under the control of eight front panel knobs and sliders. I reviewed the TT here and here , so I won’t go into more detail about its sonic capabilities.

The TT does not have built-in battery power. However, it runs quite well on a rechargeable USB battery pack. USB battery packs are readily available and are usually intended to power or recharge personal electronic devices such as MP3 music players, phones, tablets and so forth. Fortunately, electricity is electricity and the TT is happy to operate on power supplied by a USB battery pack. As long as a battery pack can supply the necessary current (usually stated in milli-amperes or “mA”), the pack should be able to power any compatible musical instrument keyboard.

Let’s explore power requirements a little bit more, using the TT as the example. KORG claim that the TT draws 550mA of power through the 5 Volt DC USB-B port. I purchased an Incase Portable Power 5400 recharging “brick.” The Incase brick can supply up to 2.1 Amps (2100 mA) of current, more than enough to power the TT. The “5400” in the product name refers to the battery capacity: 5,400 mAH. In theory, the Incase 5400 brick should be able to power the TT for nearly 10 hours. (God helps us if we ever rehearse that long!) I have been using the TT/Incase combination during practice for the last few days under light use and haven’t burned off 20% of total capacity yet.

So far, so good. But, what about a portable speaker? Unfortunately, you can’t expect to drag your keyboard into Target or Best Buy and audition portable speakers. Most of the speakers on display in box stores are wired into a point-of-sale demonstration system which plays back canned demo tracks. You won’t be able to disconnect from the demo system and connect a synth to the back of the portable speakers on display. Thus, you should audition as many speakers as possible with the canned tracks and try to find the one with the best overall reproduction without “boxiness” and weak low end.

I tried out portable speakers in-store rather obsessively and exhaustively. I eventually settled on the JBL Charge 2 Bluetooth speaker. The JBL Charge 2 has reasonably flat response and good low end without the boxiness of many small speakers (such as the higher priced Jambox Mini). The Charge 2 is a little bit chunky weighing about 0.5 pounds. It specs out pretty well: 2×7.5 Watts and 75Hz – 20kHz frequency response. Two passive radiators provide solid bottom end; bass notes are distinct with recognizable pitch.

Sonically, I’m quite happy with the TRITON Taktile and JBL Charge 2 combination. The JBL handles high energy sounds like organ and French horn without distortion and flappy speakers. The headphone output from the TT is a little too low, however, and I must turn the volume all the way up on the JBL in order to get to rehearsal-level volume. Our church group rehearsals are “unplugged” (except for me, of course), so I don’t anticipate any problems on the job. However, I’m considering the addition of a battery-powered gain stage between the TT and the JBL. The following candidates for gain stage look viable:

  • Boostaroo R234 Revolution Headphone Amplifier
  • Rolls MX56C Minimix A/V Battery Powered Mixer
  • MCM Custom Audio Compact Headphone Amplifier

The Rolls MX56C is attractive because, hey, who couldn’t use a battery powered utility mixer for other production applications? The MCM headphone amplifier has a Micro USB-B power input in addition to a 9V barrel connector. The MCM can be powered from a USB-A port just like the one on the Incase power brick.

Potentially, a fourth alternative is a guitar boost pedal. The pedal solution is viable as long as the pedal is flat and does not color the sound of the acoustic voices. I tried a Danelectro D-2 FAB Overdrive pedal with the jazz/pop voices and the overdrive does a great job of dirtying up the voices while adding gain. The TT voices are exceptionally clean and the added grit on electric pianos and guitars is especially welcome. As Moe the Bartender would say, “He ain’t pretty no more.”

There are two other aspects of the JBL Charge 2 that are worth mentioning. First, the JBL is such a chunk because it incorporates a 6000 mAh Lithium-ion Polymer battery and a 2.0 Amp USB-A charging/power port. Originally, I intended to power the TT using the JBL Charge 2. Unfortunately, there is too much digital noise on the USB power line when the TT is connected and is drawing power. One can clearly hear undesirable synthesis artifacts and noise at a completely unacceptable level when the JBL both powers and amplifies the TT. Now, I run the TT on the Incase power brick separately. I am thinking that the JBL could power the MCM headphone amplifier, hopefully without the digital noise.

Second off, the JBL is a Bluetooth speaker. (It works quite well in this capacity having tried the JBL with an iPad.) It seems like a no-brainer to send audio from the TT to the JBL over Bluetooth assuming that a Bluetooth audio transmitter is attached to the 3.5mm stereo output of the TT. This is a loser for live play, however. The transmitter must encode and compress the audio which imposes an unacceptable delay between playing a note and actually hearing the note through the JBL. I’ll stick to good ole latency-free audio cable.

The picture below shows the whole rig: the gray Incase power brick, the TRITON Taktile, and the JBL speaker resting on top of the TT. The TT does not have much clear room on top. Most of the top is taken by buttons, switches, sliders, pads, etc. The JBL’s perch is rather precarious. I would feel better having the JBL on the floor or a stable resting place nearby.

TT_and_Charge2

The entire rig fits into a Kaces 49-key gig bag and weighs 12 pounds. Finally, a self-powered rig that is as easy to handle and move as an acoustic guitar!

Polyphonic Arduino synthesizer

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!