This new addition to the ever-growing Boss Micro-Rack system has a few new tricks up its sleeve; it's a delay, a pitch shifter and it can create reverse echoes. Interested? Then read on.

The RPS10 looks much the same as the other processors in the Micro-Rack series, occupying just a single unit of half-width rack space, but some new technology has been employed to improve its performance without adding to the cost. All the signal connections are available on ¼" jacks, though the input and output are duplicated on phono connectors, and you still need an external, 9v Boss power supply, to drive the unit. The sensitivity is switchable between -10dBm and -20dBm, enabling it to be compatible with most types of semi-pro studio gear, and the input impedance is sensibly high at 1MΩ so that you can plug an instrument such as a guitar straight into it. What it doesn't have, though, is an input level control, and there's no input level metering system. Basically, what this means is that you have to take care not to under or over drive the unit.

The bandwidth in the delay and pitch shifting modes is 15kHz; most respectable, and the signal to noise ratio of 90dB (attained through companding) means that there should be no noticeable hiss from the unit unless you seriously under drive it.

As the delay and pitch shifter modes are quite separate, I'll look at delay first.

Delay

There are five delay time ranges, selectable by means of the rotary Range/Mode switch and these span 50mS to 800mS. The Fine control lets you reduce the delay time in any range by up to half, and there's a Feedback control for the creation of repeat echoes, and the inevitable Balance knob that enables you to set any desired mix of direct and effected sound. However, there's a position on the Range/Mode switch labelled Inv. This curious function causes any sound fed into the machine to be followed by a backwards echo, rather like a tape recorder playing in reverse: a function I found particularly useful for creating effects with both instruments or vocals.

Because of the generous bandwidth, the delay sound quality is almost indistinguishable from the input for most sound sources.

Rear panel features affecting the delay mode are the Effect Remote socket, and the Hold socket. By connecting optional footswitches to these sockets the effect may be by-passed, or the sound in the delay frozen into a repeating loop as required.

So far so good, but the pitch shifter opens up a new lot of possibilities.

"...my only real criticism is in the lack of input gain or metering facilities."

Pitch Shifter

Firstly let's have a brief recap on how pitch shifters work, so that their limitations can be understood. They will take any kind of signal: monophonic, polyphonic or even a complete mix, and change the pitch without altering the apparent speed: which is quite a conjuring trick. It's very easy to change the pitch of a sound by altering the speed (just like the varispeed control on a tape recorder), but how can this be done without it getting longer or shorter? The trick is to chop the sound into short sections and then, if you're reducing the pitch, to throw some of the sections away so that you have just enough left to give the correct length. Conversely, when you speed up a sound, it will want to run out too quickly, so some of the sections must be used twice to make the sound spin out. The output then consists of hundreds of segments of sound electronically spliced together, and the quality of any pitch shifter is usually measured by how well it covers up the joins. Unless you spend thousands of pounds on a very sophisticated machine, there will be some audible glitching on the output but the amount varies dramatically from model to model.

The RPS10 has three pitch shifting functions, selectable by means of the Range/Mode control, the first two, A and B, having different 'chopping rates', so that the user can choose whichever one is least obtrusive for a given programme input. The last setting, Inv, works like its counterpart in the delay section and gives a reversed character to the shifted sound.

In terms of range, the pitch may be shifted up an octave in either direction. The Feedback control may also be employed to give a spiralling pitch shift effect; every time the output is re-circulated through the shifter section, it undergoes a further pitch change until it is eventually too high or too low to be audible. The Fine tune control enables any pitch change to be finely adjusted and there is a useful Tuner Output on the rear panel which lets you use any electronic tuner to measure the amount of pitch shift you have set up.

As if that weren't enough, you can also use a synth to control the amount of pitch shift in real time. Like the Micro-Rack sampler, this doesn't use the 0V output or MIDI, but actually tracks the pitch of the instrument. All you do is set up a synth to give a clean, unfiltered, output waveform and the RPS10 does the rest. The tracking range is one octave either side of C6, but remember when you play a note on the synth, that it doesn't cause the output pitch to be the same note as the synth. What the synth is doing is controlling how far the pitch will deviate from the input signal's pitch. For example, if you play C5 on the synth, (which is one octave below C6), you will cause whatever sound is being processed to drop by exactly one octave.

In Practice

The delay section works quite conventionally, though it lacks a modulation section. 800mS is long enough for most normal delay or echo effects and the output sound quality is quite clean. The compander system certainly keeps the noise down though it's possible to hear a little hiss during low pitched sounds, due to the fact that a compander compresses the input signal and expands the output which results in very low noise during periods of silence (no input). However, the noise level rises when a signal is present, and bass sounds often contain insufficient high frequency information to mask the noise completely. This 'breathing' isn't usually a problem in practice but it pays to set the input levels carefully, to minimise the problem. Reverse echo won't be everyone's cup of tea, but I like it, especially on vocals. It would also be interesting to feed a spring reverb through this setting, to create the sort of reverse reverb effects normally available exclusively to digital reverb users.

The pitch shifter section (I nearly said harmonizer, but I think I got away with it), works surprisingly well for such a low budget device, with glitching being minimal until more than about a fifth of shift is attempted in either direction. More than this and the severity of glitching perceived will depend on the type of input program, and on its pitch; some notes seem to beat with the chopping frequency, others sound fine. Having a choice of two chopping rates, (ALB), helps enormously in minimising this problem. Like most such devices, it pays to mix in a certain amount of the original sound, to mask the glitching, but I really was impressed by how well this system performed compared with its much more expensive competitors.

"... a unit capable of out-performing many of its upmarket counterparts, particularly in the area of pitch shifting."

This unit is not stereo, unlike the pitch shifter in the Yamaha SPX-90, so you can't have two pitch shifts at the same time, but for my money the sound quality of the Boss unit is rather better when it comes to glitching and bandwidth. One of the main uses of a pitch shifter is to detune a sound only slightly before adding it to the original, and this the Boss unit does impeccably, giving a warm, vibrant sound with none of that churning that comes from chorus units trying to do the same job.

The external pitch control works well if you're careful with selecting the waveform on your synth, but it takes some practice to use it in a musically useful context. The reverse effect too is rather novel and, though you wouldn't want to use it on every song, it's nevertheless a nice effect to have at your disposal.

Conclusion

This may be a budget processor, but the design is certainly serious, and has yielded a unit capable of out-performing many of its upmarket counterparts, particularly in the area of pitch shifting. Even without the delay this would be a worthwhile product and the reverse effects are icing on the cake.

The 15kHz bandwidth and low noise, means that you could use this unit in an advanced recording situation without letting the side down, and my only real criticism is in the lack of input gain or metering facilities.

There you have it; just when it seemed that some of the other Oriental manufacturers might be getting the upper hand in the effects department, Boss strike back with a new range of products that offer the kind of performance that belies their modest size and price tag. How long will it be, I wonder, before we see a digital reverb in the Micro-Rack for under £300?

The Boss RPS10 costs £199 including VAT.

Further information can be obtained from: Roland UK, (Contact Details).