DigiTech RPX-400
A floor processor that turned into a recording studio, and made guitarists learn a little about latency.
Overview
The RPX-400 won't sit in one category. It is a floor-based guitar signal processor, a USB audio interface, a hands-free control surface for a bundled Windows recording program, and a drum machine, all in one chassis. EQ (July 2003, p.74) opened its review by admitting it took three attempts to write a single-sentence summary, and eventually gave up.
The processing engine is the familiar RP-series chain: pickup simulator, compressor, wah (driven by the built-in expression pedal), a whammy function that bends pitch with the pedal, a dual-channel amp modeling section, a three-band EQ with sweepable mid, cabinet and mic simulation, noise gate, chorus and modulation effects, delay, and reverb. EQ (July 2003, p.76) noted the modules run in a fixed series order, and that the EQ's mid band sweeps but offers no bandwidth control. Most of these are ordinary enough. The formant-based SynthTalk effect is the odd one out. EQ described it as making the guitar "speak," responding to picking dynamics in a way that's expressive but not quite intelligible, like an exotic bird with something to say.
Around 40 factory presets and 40 artist presets live in ROM, with 40 user slots in RAM. That user count is the most common complaint in period coverage. EQ (July 2003, p.76) called 128 user patches a bare minimum by its own reckoning, though it conceded the ROM presets are good and the bundled editor/librarian software provides extra storage. A phrase trainer slows down licks without pitch shifting, and a 1/8" jack doubles as a general-purpose monitor input or captures ten seconds of audio for that trainer. A drum machine with 30 patterns handles quick backing.
The connectivity is the strong suit. Guitar, mic, and stereo inputs can all be used at once, then mixed out to a PA while streaming four individual tracks of 24-bit audio over USB to a computer at 44.1 kHz, with two tracks monitored back from the computer. For a solo performer that's a useful arrangement, and EQ (July 2003, p.76) called it "hot." Routing is flexible enough to split the guitar to one set of outputs while sending the other inputs and returning computer audio to the other outputs, with or without speaker compensation.
The part people remember is the bundled Pro Tracks software, developed with Cakewalk. The three footswitches appear in Pro Tracks' control surface options, letting a player arm, record, loop record, play back, and undo without touching the mouse. EQ (July 2003, p.76) walked through the logic. Hitting Record inserts a track, arms it, and starts recording in one press. Hitting Record again stops, and a third press continues on the same track. Using Stop instead tells the program you're done with that track, so the next Record creates a new one. Play stops with an automatic return to zero, while Stop resumes from where you left off. For laying down multiple takes of a solo, the review found it about as fast as it gets. The optional FS300 footswitch can take over record functions, freeing the onboard switches for preset and amp-channel control.
Pro Tracks is a fuller program than the price suggests. It is DXi- and ReWire-compatible, handles acidized loops, imports AVI/MPEG/MOV clips, opens OMF files, and has automation, plug-in effects, and Applied Acoustics' Tassman SE virtual synth included. The ceiling is 16 stereo audio tracks (MIDI tracks, per EQ, appear effectively unlimited), 64 virtual main buses but only two aux buses, and a 48 kHz sample rate cap. Latency was measured at about 30 ms under MME and 10.2 ms under WDM. EQ (July 2003, p.76) couldn't get below 10 ms, which matters little when monitoring the processed sound going in but can produce a slight slapback when playing live through plug-ins.
The limitations, straight from the period review: no ASIO or Mac support at the time, the 40-user-preset ceiling, the 16-track cap in Pro Tracks, and that latency floor. EQ (July 2003, p.76) also warned that the sheer number of options demands quality time with the manual. The reviewer initially thought the guitar effects were too bright until realizing speaker emulation hadn't been enabled. The documentation itself got high marks, as did the installers. DigiTech's X-Edit editor/librarian is bidirectional: edits on screen jump the RPX-400's display, and edits on the unit reflect back on the computer.
The verdict from EQ (July 2003, p.76) was that no single box at this price delivered all these functions so painlessly, with the caveat that anyone who already owns a good guitar processor, audio interface, hard disk recorder, and control surface will find it redundant. Craig Anderton, writing later in the same publication, noted that as RPX-400 owners traded up to the GNX4, used units began showing up at prices tempting enough to buy purely as a control surface.
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