FACT: MIDI data comprises various commands, most of which require more than a single byte.

PROBLEM: Mixing together two streams of MIDI data cannot be achieved by simply interlacing the bytes involved.

RESULT: All bytes for a particular message must be kept together.

SOLUTION: A MIDI merger must be an intelligent device with an internal processor capable of preserving the independence of data streams - hence the price tag.

There are various scenarios which call for the use of a MIDI merger. In the case of live performance, for example, you may wish to use two keyboards or a keyboard and a sequencer which are sharing common sound modules. In the studio, you might find it necessary to edit tones on a sound module while also playing it from a keyboard. Alternatively, you may wish to merge sync data with other MIDI data when using SMPTE to MIDI Time Code or FSK to MIDI Clock converters which do not have a merge option built in. In fact, the more you think about it the more indispensable a MIDI merge box seems to become.

A few years ago, a Canadian company called Anatek bought out a range of MIDI gadgets called 'Pocket' products. Amongst them was a small two-into-one merger which, like the other devices in the range, derived its power from the voltage carried in the MIDI line. Taking their lead from this earlier product, Eye & I Productions of the USA have just brought out a similar device, called the Voice Crystal Merger Plus which feeds two inputs (INI & IN2) into a single output. It's a compact little unit measuring approximately, 8 x 6 x 3cm, and has a Reset button and an LED which is usually on but turns off when MIDI data is being processed.

Reflecting its simple design, the Merger Plus is quite straightforward in use and will happily merge two streams of MIDI note information without any audible delays. Indeed, on testing, the delay between a MIDI note at the input and its arrival at the output was found to be in the 15-30 micro-second range - which is quite inaudible. The Merger Plus transmits all data under Running Status which, for the uninitiated, is an effective data compression system included in the MIDI Specification.

Tests with System Exclusive (SysEx) data also went well - at least to begin with. 200kbyte samples from an Akai S900 were passed through the Merger without problem as were Bulk Dumps to a Roland D-550 and U-220. However, the data from some devices was corrupted during transmission and it appears that this may be down to the speed of transfer. The MIDI Specification allows for a +/-1% error on transmission speed and it seems that Merger Plus may have problems dealing with the upper limit of this.

SysEx does not allow for the merging of any MIDI information with the exception of System Real Time data such as MIDI Clock, Start, Stop Active Sensing - and so on. Consequently, it is imperative that a MIDI merger should prevent such data mixing from occurring. Interestingly, when faced with this test, the Merger Plus presented no problems providing the SysEx was sent to IN1 and any other data to IN2. Under these conditions the SysEx passed through while the other data was effectively locked out. However, when the SysEx data was sent to IN2 and other data to IN1, the data at IN1 interfered with the SysEx causing the message to be aborted. This occurred with a variety of different MIDI devices.

Being a sealed unit, it was impossible to look inside the Merger Plus, but by using a meter I was able to discover that IN1 and IN2 are electrically different. It would appear that IN1 uses a hardware Universal Asynchronous Receiver Transmitter (UART), standard to most MIDI interfaces, while IN2 is software-based. As such, IN2 appears inherently 'weaker' than IN1 and this may be responsible for the corruption of SysEx data when presented to IN2.

On a more positive note, the Reset button is a most welcome addition. The Anatek unit definitely suffered in this respect; to reset it you had to disconnect the MIDI lead to input 1. On the Merger Plus, pressing Reset causes the transmission of All Notes Off and Sustain Pedal Off messages followed by Individual Notes Off on all 16 MIDI channels - a total of 4,192 bytes.

Not nearly so welcome is the fact that the Merger Plus merges everything which arrives at the two MIDI inputs - including Active Sensing and MIDI Clock. Merging two streams of Active Sensing is nonsensical - it simply clogs the MIDI output stream (filtering at input would have been better), while merging MIDI Clocks would lead to an approximate addition of the tempos of the two transmitting devices. Many drum machines continuously output MIDI Clock and depending on the positioning of such a drum machine and a sequencer relative to the merger, problems could occur. I feel that the system used by Philip Rees on the 2M merger is far better. Here, whichever MIDI input receives MIDI Clock first locks out such data from the other input.

In other aspects too, the 2M comes out as the better unit - in fact it's virtually transparent in use. That said, at £79.95 it is even more expensive than the Merger Plus, and it does rely on an internal psu - and hence, a mains cable and the inconvenience of yet another plug to find a socket for. In this respect, Merger Plus is far easier to live with, particularly for live musicians who simply want a small box to connect into their system. For the studio, I have some reservations but these are unlikely to pose a problem in normal use. It's really up to you to decide what you need from a MIDI merger.

Price: £76.99 including VAT.

More from: Eye & I Productions, (Contact Details).