Monophonic vs Polyphonic Synths Explained: Which Should You Buy

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One of the first spec lines you see on any synthesizer is how many notes it can play at once. Some synths play a single note. Others play four, eight or more. That number, called polyphony, is one of the biggest choices you make when buying hardware, because it decides whether a synth is a bass and lead machine or a chord and pad machine. This guide explains the terms, shows how real instruments handle them and helps you decide which kind belongs in your setup.

What a voice is

In synth language, a voice is one complete sound generating path: the oscillators that make the raw tone, the filter that shapes it, the envelopes that control how it starts and fades, and the amplifier that sets its volume. Korg spells this out in its spec lines. The Korg monologue lists its structure as two voltage controlled oscillators (VCO), one voltage controlled filter (VCF), one envelope generator (EG), one voltage controlled amplifier (VCA) and one low frequency oscillator (LFO). That is one voice. The Korg minilogue xd lists a similar voice structure with a digital multi engine and an extra envelope, and it has four of those voices.

Each voice can play one note. So a synth with one voice is monophonic, and a synth with four voices can play up to four notes at the same time.

Monophonic synths

A monophonic synth plays one note at a time. Press a second key while holding the first and the synth jumps to the new note instead of adding it. That sounds like a limitation, but it is exactly what you want for bass lines and lead melodies, where a single clear line matters more than harmony.

Because all of the circuitry serves one note, monophonic designs can put a lot into that single voice. Korg describes the monologue as a monophonic beast with a redesigned envelope section, modulation routing and a filter with low end punch, plus a drive circuit for fat basses and sharp leads. It also adds features that only make sense on a single line, such as slide, which glides smoothly between notes on chosen steps, and a key trigger that plays a sequence while you hold a key. The monologue is compact, weighs 1.7 kilograms and can run on batteries.

• Strengths: focused, punchy sound, lower complexity, smaller size and often lower cost
• Best for: bass lines, leads, acid lines, sequenced patterns and sound effects
• Limits: no chords and no overlapping notes

The classic reference point here is the Minimoog Model D, a monophonic design whose layout shaped how many later synths were built.

Polyphonic synths

A polyphonic synth has several voices, so it can play chords. Four voices cover most chord shapes played with one hand, while larger instruments go to eight voices or more, which helps when you hold long notes, play with two hands or use a sustain pedal. Our look at the Behringer POLYEIGHT is an example of an eight voice analog design.

• Strengths: chords, pads, layered textures and more expressive playing
• Best for: songwriting, ambient music, pads, keys parts and anyone who plays harmony
• Limits: more circuitry per instrument, which usually means more cost and size for analog designs

Unison, chord and other in between modes

The line between mono and poly is blurrier than it looks, because many polysynths can act like monosynths. The minilogue xd shows this well. Korg gives it four voice modes:

• Poly: four voice polyphony, with a duo setting that stacks voices with detune
• Unison: all four voices play the same note, making it a monophonic synth with a thicker sound
• Chord: a single key plays a chord using one to four voices
• Arp and Latch: an arpeggiator that spreads notes over time

Unison is the important one. Stacking every voice on a single note, then detuning them slightly against each other, gives a big, wide mono sound. That means a polysynth can often do mono duty well. The reverse is not true: a monosynth cannot suddenly play chords.

You may also see the term paraphonic. A paraphonic synth can play several pitches at once, but those notes share parts of the signal path, such as a single filter or envelope. Chords are possible, but every note is shaped together rather than individually. It is a middle ground worth understanding when you read spec sheets.

Which should you buy first

Ask yourself what you play most. If you write bass lines, leads and sequenced parts, or you already have a keyboard or software instrument for chords, a monophonic synth gives you more character for less space. If you want one instrument that can carry a song on its own, with chords, pads and leads, a polyphonic synth is the more flexible choice, especially one with a good unison mode.

• Choose mono if: you want bass and lead focus, battery powered portability or a second synth to pair with a poly
• Choose poly if: you want chords, pads and the ability to cover mono parts through unison
• Consider both if: you sequence a lot, since a mono for bass and a poly for harmony make a complete setup

Our list of the best synthesizers for beginners includes both types, and our Korg minilogue xd review covers a four voice option in depth. If you are drawn to building a system piece by piece, our modular synth starter guide explains how voices are assembled from separate modules.

Where to buy

For more synth and studio guides, browse our home studio hub.