Primal Audio FM4 Review – FM Synthesis Made Easy


With FM4 Primal Audio accomplished 2 seemingly mutually exclusive tasks. They’ve created an credible instrument based on the original Yamaha DX series (complete with all its idiosyncrasies), yet designed an intuitive and powerful control interface for it that fits on a single page of an iPad. In addition to the main synth elements they’ve modeled the “defects” (aliasing, converters, distortion, etc.) of the original hardware (actually 3 different versions, no less.) This is last point is significant as the subtle “imperfections” give it some of the attitude that is missing from a lot of FM software instruments.

Primal has a good and succinct web manual available online. (Additionally they include links to some FM synthesis guides which are recommended reading if you’re not already familiar with it.)
In any case, the basic architecture is as follows: It’s a four operator FM synth with one global LFO and and arpeggiator. Both the LFO and Arp are tempo sync enabled (unlike the originals.) Each of the operators has its own control section for level, envelope, frequency, wave choice (from a handpicked selection of the originals), and modulators. The routing section allows you to pick from predetermined carrier/modulator configurations. There is an onscreen keyboard with pitch & mod wheels, and pseudo velocity control can be accomplished by finger position along each key. While I certainly prefer a physical keyboard, this one is surprisingly playable.

In practice, the FM4 is so much easier to edit than a DX7, and a lot more fun. The clean UI and well-curated preset selection might be enough for many users. Punchy basses, glassy bells, metallic pads, and retro synth percussion are within a finger’s reach. Conveniently, the preset browser latches open, allowing 1-click browsing of presets, which is super handy for quickly exploring a lot of sounds. If the preset selections aren’t enough then usually they can provide a basis for developing other sounds which can be stored in the user bank. The tempo sync of the LFO and Arp is a critical feature for me. I love it for faster rhythmic patches, as well as for setting up slower FM timbral sweeps that are nonetheless in time.

One aspect of FM synthesis is that minor adjustments in the oscillator frequency can have a large effect on the sound. Sometimes iPad knobs are not best tool for precision. FM4 has a clever solution by having a dedicated button for Fine mode, which gives finer control over the knob values. Still, it would have been nice to be able to enter frequency values numerically.

Start with 1 oscillator and 1 modulator in order to learn the synth. It’s easier to hear the interactions between the components, and you can build up from there.
FM4 sounds even better when run through analog hardware such as a good DI or preamp.

FM4 can be a great tool for your first adventure in the FM world or a fun and solid alternative to your other more complex synths. It’s not the deepest FM synth, but it doesn’t try to be. Native Instruments’ FM8 is always there if you need it.

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