The Korg Mono/Poly is a monophonic analog synthesizer that was produced between 1981 and 1984. Its distinctive feature is the four oscillators, which can either be layered to create fat sounds or allow playing with four voices. In polyphonic mode, however, all four oscillators share the same filter and amplifier stage, so it is a paraphonic synthesizer. That‘s why, despite its superior sound possibilities, the Mono/Poly was overshadowed from the beginning by the Polysix, which was launched at the same time and scored with true six-voice polyphony as well as a sound memory - both very desirable features at the time! And just a few years later, a new wave of innovative digital instruments like the Yamaha DX7 and Korg M1 followed, so the Mono/Poly was somewhat forgotten and also largely overlooked by the techno-driven analog revival. It is therefore absolutely gratifying that Behringer is resurrecting this independent synthesizer with a very characterful sound and extraordinary possibilities. Since it can be the deal breaker for some readers, a note right at the beginning of the test: Like the original, the replica also has no possibility of saving sounds!
Upon delivery, it immediately becomes clear that we are dealing with a different caliber than, for example, Behringer‘s desktop synthesizers or Korg‘s plastic bombers like OPSix and Wavestate. The package is not only relatively large for a 3-octave synthesizer, but also quite heavy. The synthesizer weighs over 10 kilograms. The design is of course strongly based on the Korg model, but with an obvious improvement: As with the Behringer Poly D, the user interface can be folded up for better operation! The robust metal housing is framed by wood and ensures a noble and chic design that is also suitable for living rooms. The large and handy knobs are in the typical Korg style of the time, as are the large buttons.
The keyboard offers 37 keys and is velocity sensitive. Unfortunately, this is only useful for external synthesizers, because the sound generation of the MonoPoly can neither handle velocity nor aftertouch. That was solved better with the Poly D! At least the two wheels for pitch bend and modulation can be routed to pitch or filter frequency, which allows at least a rudimentary automation via the DAW. Otherwise, the MonoPoly can only process the pure notes via MIDI. That‘s a bit too much vintage for our taste. The power supply via an external addapter is also less attractive, we would have liked a built-in variant here. At least there is a locking hook to protect against unwanted unplugging and cable breakage.
USB and MIDI
On the other hand, the new edition has arrived in the modern age concerning the other connections. The USB port transmits MIDI data in both directions and also provides the connection to the free configuration software Synthtribe. With Synthtribe you can make firmware updates and adjust internal settings such as synchronization. Classic MIDI jacks for IN/OUT/THRU are also provided. As with the original Korg MonoPoly, the sound generation is completely analogue without digital scanning of the control elements, so the controls do not send and receive any MIDI controllers and sounds cannot be saved. In return, the parameters can be adjusted really steplessly.
Eight large jack sockets provide a direct connection to analog equipment. In addition to CV/gate inputs and outputs, there are inputs for external modulation of filter and oscillator frequency, portamento and also for synchronization of the arpeggiator, which plays a special role in MonoPoly (more on this later). This is followed by the headphone and audio output (mono). An input for looping audio signals into the sound generator is unfortunately not available, which is a pity since the filter sounds very good. This also prevents the feedback loop, which has been so popular for its rich sound since the Minimoog.
The sound generation is like in the Korg Mono/Poly. All four oscillators are constructed identically and each offer the waveforms triangle, sawtooth and pulse wave with adjustable pulse width as well as PWM. Oscillators 2, 3 and 4 have their own controls for fine tuning, for the typical fat and floating sounds with up to four oscillators detuned against each other. With another detune control, the detuning between the oscillators can also be adjusted globally. This is particularly useful in polyphonic mode or when using chord memory, because then often only a slight and even detuning between the four voices is desired. The pulse width and its modulation by the filter envelope, LFO 1 or LFO 2 (as in the Korg called MG = modulation generator) can only be set globally for all oscillators together. In all settings the oscillators convince with a warm and fat basic sound and thus form a solid base.
The MonoPoly is not classically polyphonic in the sense that all oscillators as well as its own filters, VCA and envelopes are available for each voice. Rather, when playing polyphonic, the oscillators are distributed accordingly to the pressed keys and sent through a single filter and VCA, so for four-voice chords this means one oscillator per voice.
Because of this special feature, the MonoPoly offers three voice modes. Unison plays all four oscillators simultaneously every time you press a key, this corresponds to the typical behavior of mono synths like the Minimoog. Unison/share does basically the same thing when you press only one key. However, if you play more keys, individual oscillators are branched off for this purpose. So, for example, you can play a sound consisting of two sawtooths as a base with your left hand (generated by oscillators 1 and 2) and a melody with a pulse wave with your right hand (generated by the other two oscillators).
In polymode, on the other hand, each key only triggers one oscillator, which corresponds most closely to the way you play a „normal“ polyphonic synthesizer such as Polysix. However, filters, amplifiers and envelopes are not available for each voice, but have a global effect on all voices. If you play a note with a long attack time and a correspondingly slowly increasing volume and then another note with a slight delay, the second note starts immediately and without a slow rise. This is because the envelope was started with the first keystroke and had already reached its peak when the second note was played. Accordingly, the sound will only decay with the set decay/ release time when you have released the last key.
When you play a three-note chord and take your finger off a key, that note ends abruptly and does not decay as it would on a classic polyphonic synthesizer. To make chords decay evenly, all fingers would have to be taken off the keyboard at exactly the same time, which is difficult to implement in terms of playing technique. That‘s why there is the option to deactivate „Autodamp“. Then every single note is held and faded away after being released, resulting in a more natural sound when playing polyphonic. In this mode, however, you have to be a little careful that individual notes don‘t „stop“, i.e. continue to play permanently despite the key being released. That sounds like a massive limitation at first, and in fact you have to adapt your playing style to these special voice modes. On the other hand, polyphonic playing is possible with the MonoPoly with sonic results that are hardly feasible with conventional polyphonic synthesizers. This is especially true if you tune the four oscillators differently, set different waveforms and/or activate the effects with sync and x-mod.
Rich analog filter
Noise can be added to the four oscillators before it goes into the 24dB low-pass filter. The filter can sound very distinctive and has a pleasantly warm, round and full sound. In contrast to the classic Moog filter, even higher resonance values hardly thin out the bass range, which makes the filter very flexible. With the help of the ADSR filter envelope as well as the keytracking, which can be set to values well over 100%, the MonoPoly generates the typical bass lines and sequences for synthpop and wave in no time and impresses with its vintage sound. Another ADSR envelope is responsible for the amplifier.
Sync and cross modulation
A highlight of the MonoPoly is the effects section. Here the oscillators can be hard synchronized and crossmodulated with each other. The audio modulation takes place in pairs between oscillators 1 and 2 or 3 and 4. The modulation source for the frequency modulation of the slave oscillators can be either the filter envelope or LFO1. Hardsync and X-Mod can be activated individually or together. MonoPoly’s strength are the classic cutting sync sounds in excellent quality. In combination with cross modulation the whole thing becomes even more metallic. If you set the oscillators to different pitches and waveforms, the effects section creates complex sounds that hardly any other analog synthesizer can do. From bright bells to weird drones, retro science fiction effects and all kinds of electronic percussion sounds, a lot of interesting sounds start here. And with these audio modulations, the analog hardware also shows where the software is still lacking because plug-ins simply don‘t create these sounds that organically, even the quite successful Mono/Poly plug-in from Korg can‘t keep up with it. The same applies to the filter, especially with the harmonic saturation and distortion at higher resonance, software emulations still have a hard time.
Arpeggiator with round-robin
It gets really exciting when you play the modulated and unmodulated oscillators one after the other. And this is exactly what the arpeggiator does, optionally over one or more octaves. When you play a chord, the arpeggiator breaks that chord into its component parts and plays the notes one after the other. With a classic, monophonic or polyphonic synthesizer that doesn‘t sound very spectacular because every note is played with the same sound. With the MonoPoly, however, a simple sawtooth is followed, for example, by a hard-synchronized pulse wave, which is followed by a triangle wave tuned down an octave. Finally, there is PWM with sync and cross modulation before it starts all over again. Since each oscillator can also be individually adjusted in volume, you can create very unusual sequences and arpeggios with the MonoPoly. The arpeggiator can be synchronized to the song tempo via the analog sync input or MIDI clock. If you set the tempo very slowly via MG2 and activate the arpeggiator, the MonoPoly switches the oscillator with each incoming MIDI note. This also gives you a round-robin effect for sequences played in the DAW.
Chords can also sound very unusual if you choose different settings for each oscillator. Here the MonoPoly supports you with a simple chord memory function: You hold a chord on the keyboard, press the button and then play and transpose the chord with only one key, whereby the MonoPoly uses a different oscillator for each voice.
Yes, Behringer‘s MonoPoly is basically just a clone, but in this case the end justifies the means. After all, the original from Korg is difficult to get used and offers a potential for independent and characteristic sounds like hardly any other purely analog synthesizer on the market. Behringer‘s Mono/Poly is very close to the original in terms of sound. Thanks to its solid basic sound and great filter, it provides analog standards without any problems. But it‘s mainly the chords, sequences and arpeggios using all four oscillators and the effects section that make the synthesizer incomparable and can open up new worlds of sound, especially in combination with high-quality effects. Behringer also lets the whole package look quite appealing and equipped it with modern connections, although we would have only wished for a somewhat more extensive MIDI implementation. The price is more than reasonable for what is offered.
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