Passport Designs' Soundchaser Digital is another entrant in the 'turn your apple into a personal recording studio!' stakes. Whilst such claims make good advertising copy, it's not always clear that 'they' and 'us' have the same expectations of what a digital recording studio should be capable of. So, basically, tread carefully through the hyperbole... I mention all that for the simple reason that some of Passport's advertising (that on the inside cover of Computer Music Journal, Vol.6 No.3, for instance) goes a bit over the top (visually, anyway), and that's unlikely to have helped their reputation as purveyors of a 'serious' computer music system.

Bits & Pieces

To get your Soundchaser studio up and running, you'll need an Apple (II or IIe) - preferably with a 16K RAM card (for increased note storage), a disk drive, the Mountain Computer MusicSystem digital synthesiser boards, the Soundchaser 4-octave keyboards and Passport's 'Turbo-Traks' software. Ere we go deeper, some pricings might help to put things in perspective. Firstly, as far as basic performance is concerned, there's nothing (I think) to be gained from going for the over-priced Apple IIe. That doesn't stop some people from thinking there is, so there's now a surplus of Apple IIs that people have traded-in for the IIe. Because of that, it's relatively easy to find an Apple II for around £400 and disk drives for around £200, which adds up to a pretty fair deal when compared with BBC Micros and the like. Mind you, it helps to have a tame Apple engineer to check that such bargains aren't rotten to the core!

Moving to the MusicSystem boards, here one is helped by the price cut that occurred about a year ago. When I plumped for this product in 1981 (after reviewing it for the May '81 issue of E&MM, in fact), the MusicSystem cost the princely sum of £425. Now, it's easy enough to pick them up for just over the £200 mark, which, for 16 digital oscillators that are separately programmable for frequency, amplitude, and waveform, and then summed into stereo outputs, is pretty good value.

On to Passport's own products. The basic, ground level system is the keyboard plus '4-track performance software', which sells for £649 in the UK ($795 in the USA). This provides 4-track recording and offers an excellent introduction to many aspects of digital synthesis (this was the version demonstrated in the studio on 'Making the Most of the Micro'). However, in this review, we'll be considering the next stage up in the form of a software addition called 'Turbo Traks', which sells for £220 ($295). That's expensive by home computer standards (though of average cost when viewed alongside professional or business software), and one has every right to expect a good deal for that amount of investment.

The other thing to bear in mind is that the software upgrade effectively puts the 4-track version you got with the keyboard, into the bottom drawer! As all the keyboard consists of is a standard synth-type keyboard, wooden case, and an interface card with 3 chips on it, one's forced to the reluctant conclusion that buying the upgrade has turned an expensive keyboard into a very expensive keyboard. In fact, a £649 keyboard. It seems a bit rough that one can't buy the keyboard alone and then add on whichever software package you choose.

Booting Up

The first thing you should do on getting the system is read the manual, as this tells you in which slots to put the keyboard interface card and MusicSystem boards. In fact, as the software stands, it's configured for the interface card to go in slot 7. That's OK for the States, but, for us owners of 'Europlus' Apples, it's a somewhat thick requirement, as that slot is designed to be the recipient of the colour card that's necessary for converting Apple colour to something that 625 line TVs and monitors can appreciate. With a bit of detective work, it's easy enough to find the memory location that holds the slot address for the keyboard, and then change this to a more convenient slot. But having to do that before you've even got a squeak out of the system isn't exactly conducive to customer satisfaction, and Passport deserve a rap on the knuckles for being so unthinking towards European users of their system.

Initial cursings apart, booting-up is gratifyingly quick and efficient because of the fast version of DOS (Diversi-DOS) that's on the system disk. The advantages of speeded-up DOS also rub off on the loading of note files and sets of instruments. For instance, a maximum-sized file of 5600 notes would take around 26 seconds to load with normal DOS 3.3; with Diversi-DOS, this reduces down to just 6 seconds, which can make all the difference between enjoyment and embarrassment if fellow band members are waiting for you to load up the next song in the middle of a set!

The first screen display to appear before your eyes (Figure 2) is the all-important venue for the battle of the presets, and the complexity of the display suggests that there's a fair wadge of commands to be committed to your own memory before you're in a position to construct your own presets and store waveforms in the memory of the computer itself. That's true, but at the same time, meaningful sounds are only a few keystrokes away.

Taking the bottom row of displayed info first, the main preset is assigned to the keyboard by entering 'K' and then a value from 0-F. This switches between the 16 presets that were loaded into the Apple's memory on booting-up. At this point, you may wonder how a value from 0-F translates into the selection of one of 16 presets, and a brief explanation about the way Passport choose to assign numerical values might help.

With 8-bit systems, you've got 256 steps of resolution (0-255) when it comes to assigning values to things, whether they be volume, attack rate, or whatever. Now, one problem with any number over 99 is that it takes up three columns on the screen. Normally speaking, that's about as relevant as sliced bread to an F-plan diet, but where it becomes a major concern is when you're setting up the sort of display that attempts to squash a lot of information in a small space. That's precisely what Passport were faced with, and so they went for the sensible move of using hexadecimal-coding for all numerical values. By counting up in 16s rather than 10s, you never have to use more than two screen columns for any number from 0-255, and that translates into more info, horizontal-wise, than with decimal values. The only problem for musicians that weren't born with 16 fingers is that hex-coding may cause something of an initial communications gap between what they see in the way of figures and what they hear in the way of sounds.

The mist rapidly clears, however, and you soon get used to seeing the display cross from '9' to 'A', and then on to 'F', in the pursuit of your numeric variations. With this slice of computerese under your belt, it's then worth trying out the split keyboard feature. To invoke this, one simply keys in 'S' and then presses any key on the Soundchaser keyboard to establish the split point. Thus, pressing middle C results in 'SPLIT = 18', which, after mentally decoding to decimal, means the note 24 keys from the bottom C. The previously selected main preset will then apply to the part of the keyboard above the split, and a different preset can be assigned to the bottom part by keying in 'L' and some value from 0-F. Couldn't be easier, really - apart from the hex bit, that is.

The bottom line (so to speak) continues with the pitch bend facility and volume level. The latter affects the overall level of each set of eight digital oscillators directed to left and right outputs. The maximum usable level seems to be dictated by the mixer that you're using; for instance, a Teac 2A mixer seems to suffer from palpitations with anything above VOL = 30, whereas my Seck desk is quite happy with the full FF whack. At a guess, I'd say it all comes down to how well the input stages cope with the fast and furious transients that the MusicSystem boards seem to churn out with wild abandon. All that's of more than academic importance because of that troublesome little thing called noise. The fact of the matter is that those MusicSystem boards, clever as they might be, aren't too hot in the S/N ratio department, nor are they that reticent about producing quantization noise (a general level of grunge throughout the audio spectrum). None of this is Passport's fault (in fact, they probably make the boards perform as well as anyone could), but it does mean that one's working at a disadvantage, noise-wise, if the output level is set to anything less than maximum.

On the pitch bend front, the Soundchaser uses the keypress 'P' to select an upwards or downwards pitch bend and a games paddle (or a joystick) to actually implement it. Fine, you might think - but you'd be wrong! Apart from the limitation of not being able to bend up and down in one fluid movement (where pitch bending meets Jane Fonda, one might say), polyphonic bending is definitely out - unless you're after excruciating harmonies to give the avant garde a taste of their own medicine.

The problem is that the frequency offset read from the paddle is applied to all pitches in an identical manner. That'd be fine if there were the same number of Hertz between notes at the bottom of the keyboard as at the top, but, of course, there ain't. So, if you're playing a C at the bottom of the keyboard at the same time as middle C, and you then plunge in with an upwards pitch bend, the end result is hideously out-of-tune. In fact, the pitch bend is an excellent way of undoing centuries of equal temperament tradition, turning a well-tempered clavier into a bad-tempered clavier, not to mention achieving a similar effect on the part of the performer.

To get around this, the software should be scaling the frequency offset read from the paddle according to whatever pitches are being received from the keyboard. However, that takes a fair slice of the processor's action in such a time conscious situation as real-time digital synthesis, so one can understand why Passport have gone for a more simplistic approach to pitch bending. That doesn't make it any easier to live with, though, and the lack of scaling also applies to the modulation side of things. This means that a pleasant sine wave vibrato at the top of the keyboard becomes so gut-lurching at the bottom that a pack of Qwells becomes a handy addition to one's keyboard accoutrements.

Logical Oscillators

Switching our attention to the centre of the preset display (Figure 2 again), we're greeted with an array of crosses that's reminiscent of a plan of action for some military campaign. These crosses represent the assignment of the MusicSystem's 16 digital oscillators as 'logical oscillators', each with their own separate waveforms, to the 16 presets that we've already had a brief play with. In fact, any of the oscillators can be assigned to any of the presets by keying in 'P', the number of the preset, and then the required oscillator. This is actually a 'toggling' command, so doing exactly the same again will toggle that oscillator off the display.

Since oscillators 0-7 go to the left output of the MusicSystem boards, and 8-F to the right output, presets 0-7 (the left column, so to speak) are split across the stereo field. So, if you add some suitable ADSR envelopes to those oscillators, you'll then have some stereophonically-animated, dual-oscillator voices providing eight-note polyphony.

The part of the display immediately above the preset battlefield sets out the ADSR parameters, octave setting, and modulation options for the indicated oscillator. This is where Turbo-Traks shows its flexibilities to good effect. Keying in 'E' (for 'edit') and a value from 0-F displays the parameters for each of the 16 oscillators. Entering 'C', followed by the first letter of the function you want to change, allows you to scroll through the hex values using the right and left arrow keys. What's more, you can even do this when you're playing the keyboard (tricky with only two hands) or when the sequencer's playing back (useful in theory, but needing a lot of self-organisation in practice).

The modulation options on the right are particularly interesting. 'WAVE FM' allows for the waveforms entered into presets to be modulated by one of four user-definable waveforms, either in a continuous or one-shot mode. The latter option means that one's at liberty to put sweeping pitch offsets within the body of a sound without being forced to have it repeat over and over again. Not only that, but, by setting different values of 'FM RATE' and 'MOD AMT' for the same or different modulation waveform(s) applied to the different logical oscillators in a preset, one can end up with some glorious delayed vibrato and mixed modulation effects. As the thoroughly ingratiating manual says with undisguised glee: 'Try that on your Prophet!'. Rather silly saying that, really, considering that modulation on the Prophet is properly scaled whereas the Soundchaser's isn't!

One thing I would disagree with is Passport's use of the term 'FM'. To most people, FM implies the use of modulation frequencies at least an order of magnitude faster than what Passport are using. In fact, proper Chowning-type FM is totally impractical with the limited processing power of the Apple's 6502. Strictly speaking, then, the Turbo-Traks FM is a LFO, so don't be conned into thinking you'll get DX7-type sounds from this system!

The ADSR parameters are self-explanatory, but the couple of values to the left need a few words of introduction. 'LIN/LOG' sets the ADSR envelope to either a linear (organ-or string-like) or logarithmic (percussion-like) type. 'TIME' sets the time lag before the start of the envelope. That may seem a curious feature in the context of dual-oscillator voices, but it makes a good deal of sense when one moves into the right side of the preset arena. Here, the majority of presets have been set up with more than two logical oscillators. Because each of the oscillators can be fed with a different waveform, this 'multiple oscillator' facility can be used to produce time-changing timbres of the sort (though not the quality) common to the Synclavier and PPG Wave 2.2.

However luscious such multiple-oscillators presets might be, they're not that usable as everyday musical fodder, for the simple reason that they chew up the MusicSystem's digital oscillators like there was no tomorrow. For instance, if you insist on treating your shell-likes to the delights of preset F, you'll be down to just monophonic capability. Now, other digital keyboards like the Synergy are faced with a similar problem of having a limited number of oscillators to work into a polyphonic, timbre-changing situation, and one of the compensatory software techniques that has been developed centres around re-allocating oscillators according to what their respective ADSR envelopes are up to. Taking the example of an oscillator that's being fed with a waveform packaged in a very brief and percussive ADSR, the software needs to be capable of seeing that the oscillator only gets transient use before it's down to zero amplitude, and at that point it could then be re-allocated to another voice that needs the benefit of an extra oscillator. Unfortunately, Turbo-Traks ties up all the oscillators assigned to a preset for as long as a note is sounding or a key held down, regardless of the amplitude state of those oscillators, which is bad news when using those oscillator-greedy presets in a piece of more than a few parts.

Another single keypress ('W') moves one to the Wavemaker side of Turbo-Traks (Figure 3). Various options are available for constructing waveforms, but the principle remains the same; namely building a 256-byte waveform table and storing it in the Apple's memory.

The first option is 'CREATE'. This allows you to additively synthesise waveforms by setting the relative levels of the first 16 harmonics using a bar chart display (Figure 4) and a few twists of a games paddle. At any point, the waveform can be displayed, or one can go back to the preset display to actually try playing it. Apart from using sine waves as waveform building blocks, the 'MOVE' option allows the user to take any waveform previously constructed and make this the basis of additive synthesis.

The third and most interesting option is 'EDIT'. This provides the means of using the games paddles to 'redraw' or edit any displayed waveform (Figure 5). That way, you can have a nice, plain sine wave in the first half of the waveform cycle and a crazy sort of sawtooth in the second, though still maintaining the zero amplitude in the middle and at either end of the cycle. Lots of possibilities there...

Lastly, there's the 'SMOOTH' option, a 'digitally-simulated low-pass filter'. Again, watch out for Passport's terminology - this isn't a real-time digital filter! Instead, it simply recalculates the contents of a waveform table according to a user-selected cutoff frequency ie. removing harmonics above a certain level. This is particularly useful when you've been messing around with 'MOVE', using already harmonically-rich waveforms for additive synthesis, as it enables unpleasant aliasings to be removed without starting the CREATE process all over again from scratch. Oh yes, there's also a TUNE option to adjust A above middle C form its standard 440 Hz to virtually anything between 200 and 600.

Sequencing

Finally, the part of Turbo-Traks that arouses the most expectations - the '16-track digital sequencer' (Figure 6). Switching to this is another single-key command (the 'ESC' key, in this case), and pressing the same key again toggles back to the preset display. The manual tells one that 'Turbo-Traks is distinguished from earlier computer music systems by the incredible power and flexibility of its Sequencer'. My dictionary informs me that 'incredible' means 'cannot be believed'; Hmmm...

Each track has three possible modes, 'play', 'record', and 'off'. Switching tracks to one or other of these is achieved by keying 'M', the track number, and then 'P', 'R', or 'O'. Presets assigned to tracks can be similarly changed - and that includes whilst the sequencer is playing back - a rather nice feature.

The third column provides for per-track volume adjustment, in theory very useful for balancing things on playback, but, in practice, severely limited by the bizarre way in which it goes about it. Just 9 volume steps are provided, with 0 silence and 8 maximum, and each step upwards doubles the volume. Assuming that one had the master volume control set to VOL = 7F (half maximum), then anything less than 8 as a track volume setting will be operating the MusicSystem oscillators at no more than a quarter the maximum output, and that automatically means a further worsening of the noise level. Obviously, some sort of balancing act is necessary when you've got a number of parts vying for the ears attention, but why concentrate all the control resolution at the bottom end of the volume range? Very weird.

Actually going about some 'recording' is very straightforward. You simply select the track you want to record onto, assign a suitable preset (which can, of course, be changed on playback), and then press the space bar to start the process. Anything you play, mono- or polyphonically, will then be stored away in the Apple's memory until you press the space bar again to stop recording. Another part can then be recorded on top of the playback of the first, and the 'MERGE' facility will then add on your latest part to the notes previously stored away out of harm's reach (ie. non-erasable unless the plug's pulled out).

A metronome or click track can also be put on one of the tracks so as to help synchronising your playing. The manual informs me that this is a 'stable reference beat'. In fact, this click track should carry a Government Health Warning, because it makes you think its timing discrepancies are your own - and that leads to an awful lot of soul-searching and head-scratching. Painful.

A definite negative point for Turbo-Traks is that the sequencer is firmly anchored in the real-time camp with a complete absence of any editing facilities. This means that errors can only be corrected by going back and starting all over again. Frankly, I thought computer music systems were meant to make life easier rather than more difficult. If a note file has been created, surely it's not too much to expect to be able to display those notes and edit mistakes, change pitches and timings, and so on?

The frustrating thing is that Passport do in fact offer a non-real-time music editor, but for the 4-track software rather than Turbo-Traks. This 4-track music editor sounds impressive, and advertises itself as such ('the most powerful music editor available' - I wonder what the Synclavier would say to that?), but I'm unable to say more as it seems to be unavailable at present (the Sinclair bug of advertising before the event, perhaps?).

What about the '16-track' label? Well, yes, the software does enable you to put down 16 independent monophonic lines and play them all back at once - provided you only use single-oscillator presets. However, single-oscillator sounds are rather like consonants without vowels, or vice versa (to use the analogy of a certain Japanese keyboard manufacturer), and, for anything other than a bass drone, they're next to useless.

Now, when I first got my hands on Turbo-Traks, I thought I'd be able to do what is possible on the alphaSyntauri (the Soundchaser's direct competitor), namely using the multiple tracks rather like writing a piece on 16-stave MS paper for a limited number of players (the human equivalent of logical oscillators) doubling on different instruments. That way, I thought I could start a piece with a multiple-oscillator, contra-modulating sound on track 1, bring in some sombre bell sounds on track 2, a sequencing bass line on track 3, and then the main body of the piece on the other tracks. In fact, you can do that, but there's a major problem: if you assign a multiple-oscillator preset to a particular track, then, no matter whether there's one note or a thousand on that track, all those oscillators remain out of commission for use by other tracks and their presets.

There is a way around this - by switching off a track assigned to a multiple-oscillator preset and switching on ones you want to take over the liberated oscillators - but all this is incredibly fussy to do whilst the sequencer is playing back, and well-nigh impossible if you're actually wanting to play over it. Passport's main competitor makes sure that if a track hasn't got any more notes on it then the oscillators assigned to that track are routed to a track that does have notes.

The other possibility would be to add in a further 'mixdown' section to the software so as to emulate a computer-based mixing desk that can be programmed to remember fades, track switchings, preset reassignments, octave transpositions, and the like.

On the positive side, the transposition and speed change facilities work very well. Setting TRANS to 'Y' allows you to transpose the sequencer playback by as much as up or down an octave, by pressing any key from C below to C above middle C.

Sound Quality

This is a tricky area, because the sound of a purely digital system is very different to what one's accustomed to from analogue equipment. The quality certainly has similarities to what comes out of the better Casio keyboards, but the modulation and waveform construction options means that it's nothing like the average preset keyboard. If there's an immediately obvious letdown, it's in the noise and bandwidth department. As with the Synergy, the MusicSystem oscillators are fed waveforms at a 32 kHz sample rate. That translates into a theoretical top end of 16 kHz. Now, in order to remove clock frequencies and nasty things like that, the MusicSystem boards also have a couple of low-pass filters on the outputs. These are what are normally called 'anti-aliasing filters', though they aren't that really, as aliasings will creep in regardless of the presence or absence of such filters.

That's by the way, for the point about the MusicSystem filters is that they chop out most of what comes out of the boards above 10kHz. Whilst that certainly spells a mellow sound, it also leads to a rather bottom-heavy sound, which goes rather against the grain of what musicians expect from digital synthesis. So, my advice to anyone contemplating the purchase of the Soundchaser, or any other system using the MusicSystem boards, is to think about replacing the filters with your own. I've done this myself, and the considerable improvement in sound quality certainly warrants the effort.

Conclusions

Well, looking back on this review, I see an air of exasperation liberally dotted about. That really shouldn't be the case - especially since the bulk of the problems lie with software rather than hardware. If Passport take heed and update the software accordingly, then that'll clearly demonstrate the advantages of acquiring a 'soft' instrument; if they don't, then they're really being rather silly, because they'll be throwing away the potential of turning a fair computer music system into an excellent computer music system.

Availability: currently only from Triangle Software Ltd., (Contact Details), whose prices are quoted in the text of the review. Syco Systems are also intending to market the system, but, at present, they don't stock it, nor do they have any pricing details available. Outside the UK, contact Passport Designs direct, at (Contact Details).