RgcAudio's Pentagon I is an analog-style software synthesizer available in standalone as well as VSTi and DXi plug-in formats. It features four multiwaveform
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RgcAudio's Pentagon I is an analog-style software synthesizer available in standalone as well as VSTi and DXi plug-in formats. It features four multiwaveform oscillators, a pair of multimode filters that can work in series or parallel, and a full complement of effects, including a frequency-response simulator for modeling various speaker and amp configurations. The software also provides a Formant Filter for creating vocal effects and a Voice Modulator that turns it into a 24-band vocoder. Pentagon I is one cool synth that's inexpensive and easy to use and has enough features to keep you busy for a long time.

For this review, I used Cubase VST/32 as a VSTi host running on a Pentium III/700 MHz laptop with an Emagic EMI 2|6 USB audio interface. Under those conditions, Pentagon I sounded great. With many of its patches, I easily got ten-note polyphony without pushing the CPU meter over 20 percent. (More complex patches can quickly run the CPU up into the red zone, however.)

I also tried the DXi version of Pentagon I (which is version 1.22) with Cakewalk Sonar 2.0 XL and got similar results. By the time you read this, the DXi version should support DirectX 8 automation. You can download a demo version (on which the volume drops every few seconds) in either plug-in format from the rgcAudio Web site (www.rgcaudio.com). While you're there, pick up Triangle II, a free monophonic software synth that offers some of the same features as Pentagon I.


Pentagon I's front panel belies the ease with which you can navigate its controls (see Fig. 1). It has 114 knobs (26 of which have two functions), but many of them are repeats. For example, each of the four oscillators has the same six knobs, and having them all up front rather than in subpanels actually speeds things up. If you've programmed a synth before, a quick look at the labels will give you a good basic picture of how Pentagon I works. Skimming the manual, which is short and well written, will introduce you to the idiosyncrasies that make Pentagon I more than just an average synth.

Pentagon I's sound engine is a multiwaveform oscillator with 13 waveforms as well as white noise. The usual shapes are included along with some harmonically unusual waveforms. For example, some waveforms contain only multiples of the third, fourth, or fifth harmonic. Pentagon I also offers four slots for importing user-defined wavetables, which come in two varieties: full wavetable and single cycle. You can easily generate your own single-cycle wavetables in most sample editors (such as Syntrillium Cool Edit and Sonic Foundry Sound Forge). Full wavetables contain a separate waveform for each MIDI note (yielding 128 single-cycle waveforms) and are a little more complicated to build. You can download 50 of them from the rgcAudio Web site, and you can request a Cool Edit plug-in for creating your own.

The oscillators offer several unusual options. You can use the Key Sync feature to synchronize the start position within the waveform (the phase) with the onset of notes. That allows you to create reproducible new waveforms by combining two oscillators with different tuning, waveshapes, or phases. (If the oscillators were free running, which is another option, you would not get the same waveform each time you played a note.) As the control panel indicates, the oscillators come in pairs; the top oscillator in each pair can modulate the bottom one using ring modulation, FM, or hard synchronization. (Hard synchronization forces the bottom oscillator's waveform to restart every time the top one's does.) Finally, the top oscillator in each pair has a Multi mode, in which the oscillator actually becomes eight oscillators whose detuning is set by the Phase knob (see Fig. 2). That produces the fat sounds usually associated with unison mode on classic synths; with Pentagon I, however, it also works polyphonically.

Pentagon I offers a number of pitch-modulation options; among them are a dedicated LFO, a dedicated ADSR generator, a Random knob for detuning the oscillators, and flexible pitch-bend and portamento schemes. For example, portamento can be normal (always applied) or fingered (applied only to legato notes) and variable or fixed time (time does or does not depend on pitch difference). Pitch bend can be asymmetric (with unequal ascending and descending amounts), applied to only the highest or lowest notes of a chord, or restricted to notes being held down by the user (not applied to sustained or released notes). Obviously, someone at rgcAudio is a guitar player.


Filters pop up everywhere in Pentagon. The main Filter section contains two resonant multimode filters that can be arranged in series or parallel. (You can also use just one filter or turn them both off.) Each filter has its own bipolar ADSR envelope with Velocity tracking. Separate controls set the amount of cutoff modulation by MIDI note number (aka key tracking), Aftertouch, Breath Controller, and Mod Wheel.

A dedicated filter LFO offers the usual waveshapes as well as user-defined (imported) waveforms. All of Pentagon I's LFOs can be synchronized to tempo and have separate offset, delay, and fade-in controls. They also have separate settings for MIDI Aftertouch, Breath Controller, and Mod Wheel control of modulation amount. The filter LFO's only drawback is that it has only one modulation-amount control for both filters. Being able to apply different amounts and polarities to parallel or series filters would be a welcome addition.

Pentagon I's Simulator offers a selection of 19 complex filters that model the frequency response of various environments (see Fig. 3). Simulations include guitar speakers and amps, radio speakers, artificial environments, EQ curves, and sample-rate limiters. The Simulator offers one of the easiest yet most effective tweaks you can make to a program. It's especially effective when you're doubling a part using two instances of Pentagon I with the same program.

Pentagon I's other special filters are the Formant Filter and the Voice Modulator. You can turn both of them on and off using the context menu that appears when you click in the status display at the top center of the control panel (see Fig. 4). The Formant Filter simulates the filtering effect of the mouth when vowels are spoken. When the Formant Filter is turned on, the Drive knob selects the vowel sound. You can assign any MIDI Control Change (CC) message to the Drive knob, but you can also use the filter LFO to modulate the Formant Filter. In that case, the filter's V-MOD knob (the alternate state of the MOD knob) sets the LFO amount.

The Voice Modulator is actually a 24-band vocoder. It requires that you use the Pentagon I effect plug-in as an audio-track insert. The audio on the audio track (or live audio input to the corresponding audio channel) then becomes the modulator (which is typically speech), and the selected Pentagon I program becomes the carrier. Your host program must be able to send MIDI note messages to effects plug-ins in order to use Pentagon I as a vocoder. Although the Voice Modulator doesn't have all the bells and whistles of a full-featured vocoder (such as band-shifting and the ability to handle fricatives), it will produce recognizable speech and is very effective with other types of program material such as percussion loops.

The MP3 file “PentaVox” at www.emusician.com illustrates both the Formant Filter and the Voice Modulator. The clip is in four segments. The first is a straight Pentagon I pad program. The second adds a randomly low-frequency-oscillated Formant Filter. The third uses a drum loop to vocode the straight pad sound. The last segment vocodes the formant-filtered pad.

The other filters Pentagon I offers are a 2-band quasi-parametric EQ and tone controls built in to its Drive and Delay effects. The EQ offers as much as 15 dB cut or boost for adjustable low (30 to 230 Hz) and high (3 to 9 kHz) bands. The filter in the Drive effect is high-cut as you would expect, and the filter in the Delay can be either low- or highpass.


In addition to the quasi-parametric EQ already mentioned, Pentagon I has Drive, Chorus, Delay, and Spread effects modules as well as a dedicated Amplifier LFO for tremolo and autopanning. Drive is a typical clipping overdrive circuit.

The Chorus module offers three levels of both chorus and phasing: Normal, Stereo, and Four-Voice. In all modes, you can set the delay time from 0 to 30 ms (adjustable in 0.01 ms increments), and the sweep LFO has a range of 0.01 to 5 Hz. The effects range from very subtle chorus to extreme phasing.

The Delay module has stereo (separate delays for each channel), Ping-Pong, and LRC (left-right-center) modes. You can adjust delay times in 0.5 ms increments from 0 to 1 second, or a maximum of 4 seconds in Sync mode. At the range's low end, you get interesting resonator effects with high feedback settings. Larger delay-time settings result in the usual kinds of bouncing around.


Pentagon I's interface has a number of user-friendly features. The gray strip at the bottom of the control panel functions as a keyless MIDI keyboard; you can click on it for single notes and drag across it for glissandi. The current voice count (as many as 64 notes per instance) is always displayed at its right end.

You can move knobs with circular or linear mouse motion. In circular mode, they have inertia; click a position far from the current setting, and the distance the knob moves will depend on how long you hold (you can disable inertia from the Options menu). You can set a default mode for all knobs, then temporarily toggle to the other mode using the Alt key. If you prefer linear motion, as I do, but also want inertial clicking, that is a great feature. Control-clicking on a knob will reset it to its default value, and Shift-clicking allows fine adjustment (in linear mode only).

As mentioned, many controls have two functions, as indicated by a blue label. Clicking on the label toggles the function as well as the label text. Passing the mouse over any knob shows both its function and setting (in meaningful units such as percent, milliseconds, or decibels) in a status display at the control panel's top-center.

Pentagon really shines when it comes to MIDI control. You can assign Aftertouch, Pitch Bend, and any MIDI CC message to any knob by Shift-right-clicking the knob and selecting MIDI Learn from a pop-up menu. Once MIDI has been assigned, you can use the same menu to restrict the knob's range and to reverse its polarity.

Pentagon I goes way over the top by allowing you to assign multiple MIDI messages to any knob as well as assign the same MIDI message to multiple knobs. That means you can set up extremely complex MIDI control schemes; for example, to create a variable-bandwidth filter, you could assign the Mod Wheel to the filter-cutoff frequency of both filters with opposite polarity.

The MIDI configuration is not saved directly within Pentagon I programs (although it would be nice). In the DXi version, however, it is saved within the song file. Pentagon I can also store as many as ten MIDI configurations and allows you to copy and paste among them.


It's hard to find anything to fault about Pentagon I. Analog-style software synthesis is in an increasingly crowded field, but Pentagon I offers several unique twists. Among them are complex MIDI control, custom waveforms, dual filters, numerous modulation options, and unique effects such as the Simulator and Formant Filter. It isn't free, but you get a lot for your 99 bucks. If you're on a Windows machine, you should certainly give Pentagon I a test-drive.

Minimum System Requirements

Pentagon I

Pentium II/300; 64 MB RAM; Windows 95/98/2000/ME/NT/XP


Pentagon I 1.21 (Win)
software synthesizer


PROS: Great sound. Extensive MIDI control. Good selection of filters and effects.

CONS: Requires a fast CPU. MIDI control setups not saved with patches. Filter LFO applies same amount to both filters.


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