ADDING ON YOUR SPECTRUM

Our review team take a brief look at some of the hardware add-ons fir the ZX Spectrum.

Now that the ZX Spectrum has well and truly established itself on the micro market, it is amply supported by a wealth of hardware add-ons. Most of these peripheral devices have been manufactured by the people who supported the ZX81, but just as the Spectrum has attracted new users with its prowess, so too has it attracted a new following from the add-on manufacturers.

In this brief guide, we have not tried to cover all the devices currently available on the market but rather give you a flavour of the technology you can add on to your Spectrum. As joysticks are an obvious favourite, these have been covered in some detail whereas RAM packs are fairly standard and so have only been briefly touched on. Also included in this section area number of quite specialised add-ons like sound units and a digital tracer.

If you own a Spectrum, you will no doubt have begun to realise the potential you hold in your hands. Over the next few pages you will hopefully see further applications for you and your computer to explore.

This is another product which first cut its teeth on the ZX81. Plugging this unit into the back of the Spectrum, you can make the S-Pack work wonders in seconds. With a few simple key presses, it announces 'This is Digitalker' (which is what it used to be called!).

The unit comes supplied with a total vocabulary of 71 phrases, numbers or letters. They at first sight do not seem very inspiring, but at closer inspection, they all seem to be fairly useful. Should you get bored with these sounds, DCP have three other Word Packs which are supplied as ROMs and just need to be allowed for in your programming for inclusion in a new program. These Word Packs are priced at £14.95 each, so check out that you are interested in the complete vocabulary before looking too closely at the unit.

The S-Pack is housed in a black box with a good edge connector and an expansion connector should you wish to hang anything else on the back.

The S-Pack, complete with Word Pack 1, is priced at £49.95. Further details are available from DCP Microdevelopments Ltd, 2 Station Close, Lingwood, Norwich NR13 4AX.

TALKBACK: SPEECH UNITS ASSESSED

When you find you get to the stage where you find yourself talkiing to your micro, it helps if it answers back!

From the time the Daleks trundled across our TV screens muttering "Exterminate, Exterminate" in their chillingly inhuman voice, I have been intrigued by speech synthesizers. At the time of writing, and to the best of my knowledge, there are six different units on the market to enable your micro to answer you back. Two others have recently lost their voice, I asked why, but the suppliers aren't talking.

The units on the market at the moment are "Sweet Talker" from Cheetah for both ZX81 and Spectrum, "Micro Speech" from Currah, "Orator" from Fuller, "Vox Box" from Datel Electronics, "Chatterbox" by William Stuart Systems, and "S-Pack" by DCP.

I contacted all of the above companies and those units that were supplied for review I sent to different reviewers for their independent comments.

For your own assessment here's what they thought....

Unlike most speech units on the market today the DCP Speech unit does not create words nor does it use allophones.

The unit contains a prerecorded chip which contains about 70 words which cannot be added to or changed.

The words have been created by first having been spoken and then changed into a digital form, they can be recalled by the user by simply using an OUT statement, ie: OUT 255, 34. The advantage of this is that you get a clear reproduction of sound unlike the allophone system.

You can buy another 3 chips which contain another 70 words each, but will cost you another £12.95 each. These are just slotted into place inside the box. The DCP speech unit will fit the ZX81 and the Spectrum, and fits straight onto the output port.

You can also fit an external speaker if you wish, which can be adjusted by a volume control. The chip that comes with the unit contains the alphabet plus numbers from 1 to 20, and also the words hundred, thousand, million. So in fact you can construct any number you wish.

The other three chips contain words like control, equal, flow, gallon, high, inches, kilo, limit, lower, stop, emergency, pico, kilo and so on. This gives a total of about 280 words, Using the unit is very simple and it does add a new dimension to your programs, although you can bet the one word you want won't be available.

The unit itself costs £29.95 and if you were to buy the unit and all the chips it will cost you nearly £70, need I say more?

SPECTRUM SPEAKERS

The word is that attaching any old speech synthesiser to your Spectrum will allow you to have cosy chats together. Henry Budgett determines where this is one of the first signs of madness.

For years science Fiction films and futuristic novels have depicted an era when man and machine can communicate in perfect harmony. The reality, of course, is slightly different. While speech recognition has yet to he fully developed (ACT's latest Rascal notwithstanding), chip-based speech synthesis has been both mastered and available for several years. Until recently the computing power needed to produce human-sounding utterances was substantial. Now almost every home computer is capable of being equipped to talk back to its owner at a price that won't even break the average piggy bank.

SOUNDING OFF

When we speak we produce three distinctly different types of sound. The most obvious are the 'voiced' or vowel-type sounds; oo, ar, ee, and so on. These are produced by air from the lungs making the vocal cords vibrate. The frequency of this vibration determines which vowel sound we hear.

The second group is the unvoiced or 'fricative' sounds; ss, sh, t and ff. Here the air from the lungs rushes past the vocal cords without making them vibrate and the frequency produced is controlled by the positioning of the lips and tongue. Finally there's silence or, to be more precise, the minute gaps that occur within words (for example six, eight) where we change from voiced to unvoiced and vice versa.

FAKING IT

In order to generate speech-like sounds, the electronics designers generally go for one of two methods. The first - and until recently the most common - is synthesis by rule. If the frequencies contained within speech are analysed it's possible to devise a system of rules that allow us to re-create any sound from its basic frequencies.

These 'building blocks' of sound are called phonemes and by using them in various combinations any word can be constructed. The individuality of a human speaker tends to be lost when speech is generated like this but the words can be clearly understood. Because the synthesis rules for each phoneme are built into the equipment, the user has simply to supply a list of phonemes to be spoken. It's then possible to generate complete sentences instantly, simply by calling up a string of stored phoneme commands. In reality these phonemes tend to be called allophones; this is because the various building blocks sound different depending on their positioning within a word or phrase. However the principle's much the same.

The second method for generating speech relies on the fact that the human ear and brain are very good at filling in gaps. The speech we hear over a telephone line is (British Telecom permitting) perfectly understandable. Yet technically the quality - the range of frequencies we can hear - is only one-fifth of what we'd expect from a standard hi-fi system. We understand what's being said only because our brain does the job of filling in the gaps.

With the fall in cost of computer memory it's now possible to convert speech into digital information compressed many hundreds of times by a wonderful mathematical technique called Linear Predictive Coding. The resulting numbers representing the original speech are stored in a ROM. To get any of the stored words out again as speech is easy; we simply give the computer the address in memory of the word and the digital information is recovered and converted back into sound, and because the original speaker's words have been stored, all the personal characteristics remain. That's why Acorn's speech chips for the BBC Micro really do sound like Kenneth Baker.

WHAT'S THE USE?

The commercial uses for speech synthesis are so many and varied that it's just about impossible to list them all. Looking just at the tip of the iceberg it can be used to replace taped announcements at railway stations and airports; in America it's widely used on the telephone system to inform callers of misdialled numbers and engaged or withdrawn services. Speech synthesis units are also being incorporated into cars like Maestros and Montegos as part of the standard instrumentation so, as well as being something of a sales ploy, they can provide warnings the driver can hear without having to take his or her eyes off the road. A major contribution to road safety perhaps?

As far as we are concerned in the home computer and electronic games market, speech synthesis is generally used to enhance games. Scores can be read out and warnings of imminent enemy attack can be given to warn players leaving them free to concentrate on the tactics of the game. Of the five speech units under review here, four of them use the phoneme system and one the stored speech method. Let's take a look at how they succeed in fulfilling their purpose.

SUMMARY

If you're looking for a means of adding a voice to your Spectrum and of incorporating the facility either into games or just for fun, then the Currah MicroSpeech is almost certainly going to be the best buy for you. It's also got the largest number of games already written for it if you prefer to use shop-bought software. Another of its clear advantages over the other units is the addition of a BEEP amplifier for putting the sound through the TV.

For those of you who haven't yet bought a joystick controller or a sound generator and fancy a speech synthesiser at the same time, then the Fuller Box/Orator combination - though expensive - offers the lot in one package.

Serious users of speech output have an equally clear-cut choice. The superior quality offered by the DCP S-Pack's Digitalker chips make this the logical buy for anyone using the Spectrum as an annunciator rather than as a games machine. The manuals supplied aren't good enough by far, but the Digitalker chips are more versatile than you might think, so if you buy this one get in touch with National Semiconductor for the real data.

Of the remaining two units, the Cheetah offers a built-in amplifier and speaker whereas the Timedata unit doesn't; their respective prices reflect this. Neither of them comes close to the overall 'usableness' of the MicroSpeech and they both lack the BEEP amplifier and keyword voicing.

S-PACK
Price: £29.95 (Extra Word Packs £12.95 each)
DCP Microdevelopments
2 Station Close
Lingwood
Norwich
NR13 4AX

HARDWARE: Based on the National Semiconductor 'Digitalker' system this was the only review device to use compressed speech. In terms of producing intelligible utterances it wins hands down over all the rest but there are several reservations.

It comes housed in a 75mm by 110mm by 45mm plastic box and mounts horizontally behind the Spectrum. In its favour is the provision of an expansion bus connector but, unfortunately, the rest of the construction is fairly low-grade. Inside are two PCBs, one providing the bus and the other the speech synthesis components. An internal speaker is provided along with a 3.5mm jack socket to connect the device to a larger external speaker. The volume control is an edgewise potentiometer, in my view a cheap and nasty approach.

The speech chips are all socketed and there's provision for installing four vocabulary ROMs... our review model had all four fitted. When I first tested a Digitalker system some three years ago these were the standard chips. Although the price has fallen dramatically (the experimenter kit was then about £130 with two vocabulary ROMs), the repertoire hasn't. It may be worth contacting National Semiconductor direct to see what else it can offer (UK offices are in Bedford).

The speech quality from this unit is excellent. It's easy to hear that the log-on message "This is Digitalkcr" is spoken by an American female and the rest of the words in the first two ROMs are spoken by an American male. I'm also pretty sure that there are two other people speaking on the second pair of ROMs, which is an indication of the sort of information a digitised speech system contains that you don't get from an allophone system.

SOFTWARE: Er, there isn't any! You just OUT the required word number to the appropriate port and the device says it.

MANUAL: Not a lot of use, I'm afraid. The four A5 sides tell you how to use the thing, but miss out on all sorts of interesting details. Your best move is to get the National Semiconductor data sheets (usually free) and find out from them how to string words together, get parts of words and a whole lot more besides.

SUMMARY: For pure speech that's immediately understandable this wins hand down. On the other hand you may want words that aren't in its vocabulary and, as it stands, there's no way to make them. Therefore, it's main use would be in a dedicated system announcing times and other numeric data - it's not much good for games and so on.