Electron owners are always striving to expand their micros the reach the capabilities of the BBC Micro. There have been upgrades for items like memory, speed and Mode 7 in the past but until now there's been no sound add-on that does anything more than allow the volume to be altered or headphones to be connected.

Now that's changed, with the release of Complex Software's Sound Expansion which gives the Electron the same sound capabilities as a BBC Micro.

This means that Electron owners can now enjoy hearing effects like more than one note playing at a time - chords - and volume adjustments - fades. Added to this the unit also has a volume control and sockets for headphones and connection to a hi-fi.

The Sound Expansion cartridge plugs into the Acorn Plus 1/AP1 or Rombox+. It has a built-in speaker for slight volume and quality increase and comes complete with a one page user guide and demonstration tape or disc - remember to state which you want if you order one.

The single sheet user guide is sufficient to get your started and use the unit with current software, but a more detailed description of how the SOUND and ENVELOPE commands work would have been usedul. A good source of information is the BBC Micro User Guide.

Installing the unit is easy merely involving plugging the cartridge into an expansion slot. Then entering *HELP SD gives a list of the three new star commands:

Demonstration programs supplied with the unit show off its capabilities well and even though they're not of a very high musical standard they illustrate what is possible.

As the whole idea is to give the Electron the sound capabilities of a BBC Micro, the next logical test was to see if some of the programs written for that micro work.

I tried several games from The Micro User and found that if they worked but only gave dull beeps with the Sound Expansion switched off, they gave the effect the programmer had intended with the unit on.

One particular program - jingles from the December 1989 issue - has never been worth considering for the Electron before, but with the new expansion the micro became a tuneful keyboard. Many Electron games are cut down versions of BBC Micro ones. As the Electron ignores the last six parameters of the ENVELOPE command, they are often left in but have no effect.

This means that some games suddenly produce great new sounds when the unit is connected. Unfortunately, not all the games give the desired effect, because some use different methods and other may just have the last few ENVELOPE parameters set to, say, zero on the Electron version.

I tried the unit with Perplexity, which was reviewed last month. The first problem is that some Superior games will not work with the Acorn Plus 1/AP1 attacked, and as the Sound Expansion plugs into it the unit can't be removed.

The cure - and this is a useful tip for running most recent Superior games on an Electron with Acorn Plus 1/AP1 - is to LOAD the first program on the tape rather than CHAINing it. Then type 30 to remove line 30 and RUn the program. When I did this with Perplexity things appeared to go wrong a couple of times as the tape loaded and there was a high pitched beep from the expansion - the volume control was handy here. However, once the game was loaded it worked well.

The tune on the BBC Micro version has been removed but the sounds that are there have a much better depth to them. As I'd hoped, the game still appears to have the BBC Micro SOUND commands in it.

Another game that is vastly improved by the unit is Elite. Electron owners can now hear the three channels and the fading of sounds that were previously only heard on the BBC Micro.

The unit is claimed to operate with Superior Software's SPEECH! but I couldn't get this working. Complex Software Systems assures me that, to work on an Electron, Speech! just needs a small change and a routine to do this will be on the utilities disc in the future. The unit seemed to function with other Electron add-ons like the Slogger Master Ram Board 64K memory expansion and didn't seem to clash with any software I tried.

Apart from the lack of a good manual I've only one minor niggle. With a disc drive connected to the rear cartridge slot of my Plus 1 and this in the front there's no room to plug in more cartridges.

I consider this unit so useful that it should be left in all the time - as should the disc drive - so I've now nowhere to plug cartridges that are occasionally used.

Sound Expansion is worthwhile, even if it's only used to increase the sound capabilities of your Electron. Add to that the fact that it gives you a better speaker control of the volume together with headphone and hi-fi sockets and the unit becomes essential.

Pete Davidson