Primal Audio FM4 reviewed: a TX81Z on your iPad

March 27, 2015

Over the years, I’ve owned countless hardware synths, both analog and digital. There are a few that I just had to keep because they’re utterly unique. One of those is a Yamaha TX81Z. For many synth aficionados, the 81Z was a bit of a trifle, even in its day. As Yamaha’s FM synths go, it only had four operators, basic envelopes, and crunchy digital-to-analog converters with more than a whisper of noise. But it was also one of the most popular synths of the early house and rave scene. In fact, its “Lately Bass” preset was a cousin of the DX100’s “Solid Bass” patch that anchored countless tracks, notably Orbital’s “Halcyon and On.”

So when Primal Audio’s new FM4 came out, I immediately purchased it to see how close it got to the sound of a real TX81Z. The specs indicated that they actually spent time and resources on recreating the distinctive character of the Yamaha D-to-A converters, so I was more than a little intrigued.

The user interface is brilliantly designed for an FM synth. Everything is on one page, so there’s very little fussing around whether you’re modifying one of the 128 factory presets or creating your own. It’s all in plain view and as a sound designer, I love that kind of attention to detail.

As with the 81Z, there are four operators, each with the same eight unique waveforms that really defined the sound of the Yamaha. Every operator includes the same ten parameters, neatly laid out in a row: level, ADSR envelope, tuning, waveform, LFO depth, velocity sensitivity, and keyboard tracking. With all these parameters within easy reach, it’s quite clear what’s going on with your settings as you program.

Another lovely design touch is the way Primal Audio implemented the TX81Z’s algorithm selector. As you flick through these routing options, there are clear lines indicating the configuration next to each operator’s on/off switch, so you can always see at a glance which ones are carriers and modulators.

Also included is the 81Z’s selection of eight mircotuning modes, which includes academic options such as Werckmeister and Valotti-Young. While most users will likely ignore these options, there are others who will be in heaven because of their presence here.

The LFO controls include the TX81Z’s waveforms, along with both tempo-sync and triggered modes. Even the simple ramp-based pitch “envelope” is in place.

Primal Audio’s enhancements to the architecture are straightforward and functional. There’s a unison knob that can double, triple, or quadruple-layer FM4’s voices for an added thickness that was beyond the original’s scope. A “model” switch that toggles between three different Yamaha D-to-A characteristics, with the most extreme option reducing the presence and adding digital noise to the output, just like a vintage unit. Finally, there’s a simple arpeggiator with up, down, up/down, and random modes. I’ve always loved random arpeggiators, so this addition really made me smile.

As for iOS features, CoreMIDI and Inter-App audio are in place, with Audiobus planned for an update by the time you read this.

After reviewing iOS apps for over five years, I’ve gotten pretty finicky about “me-too” apps that don’t really bring anything new to the table. FM4 is anything but that. It’s a distinctive soft synth that does a fantastic job of capturing the sound of Yamaha’s four-operator FM synths of yesteryear, with the added bonus of a brilliantly designed interface. This may be Primal Audio’s first synth, and I doubt it will be their last.


Spot-on recreation of Yamaha’s classic four-operator synths. Eight microtuning modes. Brilliantly designed user interface makes editing sounds a breeze. Unison mode adds needed thickness to FM sound. 


You still need to have a working knowledge of FM to edit your sounds intelligently.

Bottom Line

Better than a real TX81Z in every way.

$9.99 download |

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