DigiTech RPx400

It’s time to erase the line between recording and playing

I've tried for 30 minutes to write an opener for this review. I wanted to encapsulate the RPx400 in one simple, easy-to-understand sentence from which the rest of the review would flow. (I bet DigiTech’s marketing department would like to be able to do that, too!)

But I give up. The RPx400 is unlike anything else, although it comprises familiar elements. It’s a floor box or desktop signal processor designed for live or studio use, but it’s also an audio interface that streams four channels of 24-bit audio to a computer, and plays back stereo from your computer for monitoring through various outs, including a built-in headphone jack.

We’re not done yet: it’s a guitar-specific control surface for a sophisticated Windows hard disk recording program bundled with the RPx400. Arm tracks, go back over parts, go into record, and work the transport — all hands-free — from the unit’s footswitches. And there’s a drum machine with 30 patterns for quickie backup, along with a phrase trainer that slows down licks without pitch shifting . . . and the ability to do re-amping. Essentially, the RPx400 integrates the functionality required for recording, signal processing, and live performance. Give it a task, and the usual answer is, “Sure, why not?”

Is it for beginner, intermediate, or advanced players? Well, the price makes it affordable for beginners, the functionality makes it useful to intermediates, and even experts will find the hands-off control a valuable tool for capturing inspirations. (Note to DAW manufacturers: please support the RPx400 as a control surface in your next revs, okay?)

No wonder I couldn’t get this all into one sentence.

The sidebar lists the ins and outs, but note that you can use the guitar, mic, and stereo ins simultaneously, then send the mixed out to a PA while recording them into a laptop as four individual tracks, streamed as 24-bit audio over USB.

For solo performers, this is hot. There’s also a 1/8" jack that serves as a general-purpose monitor in, or can record 10 seconds of audio into the RPx400 for the phrase trainer feature.

There’s more to the outputs than expected. For example, you can route the mic and line ins to the output without processing. Or with processing. Or with the current preset’s delay and reverb modules. Also, you can route all the inputs to both output pairs but enable speaker compensation on only one of them . . . or both of them. Or split the guitar to one set of outs, and the other inputs — as well as audio returning from the computer — to the other outs, with or without speaker compensation. There’s more, but I’m starting to get dizzy.

DigiTech’s RP-series guitar processing is pretty mature; modules, connected in the following series order, include a pickup simulator, compressor, wah (controlled by the built-in expression pedal), whammy (a “bend pitch with expression pedal” processor), dual channel amp modeling section, 3-band EQ with sweepable mid (no bandwidth parameter, though), cabinet/mic simulator section, noise gate, a rich selection of chorus and modulation effects, delay, and reverb.

Although most of the effects are common, a couple effects make your guitar “speak.” These are formant- rather than vocoder-based. SynthTalk is a standout, as it relates to the dynamics of your playing and can be very expressive. The result is sort of like an exotic bird speaking — you’re not quite sure what it’s saying, but it’s saying something.

The expression pedal is assignable to one of umpteen different parameters within a patch, and you can change its function from wah to something else, hands-free, in real time. An A/B footswitch selects among two amp channels (with their own amp model, cabinet, modeled mic position, and EQ).

There are 40 factory and 40 “artist” ROM patches, along with 40 user (RAM) patches. I’m the kind of guy who thinks 128 user patches is a bare minimum. However, there are two mitigating factors: the ROM presets are pretty good, and there’s a bundled editor/librarian program for additional program storage.

The software, installers, and documentation get very high marks, but follow the instructions to the letter; the procedure differs slightly for different operating systems. I was up and running in minutes on Windows XP, getting about 30 ms of latency with MME, and 10.2 ms with WDM.

DigiTech’s X-Edit Editor/Librarian is a useful, stable program that simplifies the editing process. Because the USB control is bi-directional, the RPx400’s display jumps to, and shows, edits made on-screen; but also, editing a RPx400 parameter is reflected on your computer. This is good stuff.

The bundled hard disk recording software is stellar. Pro Tracks, developed with Cakewalk, is a remarkably full-function hard disk recording/MIDI program. It’s DXi- and ReWire-compatible, handles acidized loops, imports AVI/MPEG/MOV video clips, opens OMF files, does automation, comes with several audio plug-in effects, and includes Applied Acoustics’ Tassman SE virtual soft synth.

There’s a limit of 16 stereo audio tracks (MIDI tracks appear to be unlimited; I stopped trying to reach a limit after creating 400 tracks). You can have up to 64 virtual main buses, but only two aux buses. Input monitoring is supported for playing live through plug-ins. Sample rate tops out at 48 kHz, but the lack of 96 kHz operation is likely not a deal-breaker for most people.

Arguably, the coolest part is that the RPx400 also shows up in Pro Tracks’ control surfaces options. With this, the three footswitches control Stop, Return to Zero, Record, Play, and the ever-popular Undo. (The optional FS300 footswitch controller can take over the record functions, leaving the RPx400 switches for doing preset and amp channel control.)

There’s some intelligence to this. If you press Record, Pro Tracks inserts a track, arms it, and starts recording — one button press! If you stop by hitting the Record button a second time, then hitting Record again will continue recording on the same track. But if you use the Stop switch to stop, the program assumes you’re done with that track. Next time you hit Record, it will create, arm, and start recording on the next track.

If you hit Play, the track begins playing. Use Play to stop, and there’s an automatic Return to Zero. But use the Stop button, and if you hit Play, playback resumes from where you started.

What this all means is that you can arm, record, loop record, play back, and undo tracks in rapid-fire succession; if you want to lay down multiple takes of a guitar solo or vocal, this is as fast as it gets.

Also note the plethora of routing options — guitar processed through one USB pair, split with dry mic and dry guitar each down one channel of a stereo pair, re-amping where you process a recorded guitar track through the RPx400 and re-record it, and so on.

I couldn’t get the latency below 10 ms but this is usually irrelevant, because you’ll be monitoring the processed sound you’re recording as it goes into the computer, not after it passes through the system. However, for live playing through plug-ins (the RPx400 can’t provide every possible effect you might want), you may notice a slight slapback effect.

This is a surprising box. Someone really scoped out what a guitar player needed to get involved in hard disk recording on a painless level, from installation, to interfacing, to effects, to recording. The only caution is that the sheer number of options requires some quality time with the manual. For example, I initially thought most of the guitar effects had too much high end — until I realized I hadn’t enabled speaker emulation. Doh.

Granted, if you already have a good guitar processor, audio interface, hard disk recording program, and control surface, then the RPx400 is redundant. But if you don’t, no one box delivers all these functions at this price point . . . and makes it this easy to get into guitar-friendly hard disk recording.