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Soundtracs PC MIDI mixer

More and more mixer manufacturers are waking up to the benefits MIDI can offer in a mixdown situation by incorporating MIDI-controlled muting on their products. Engineer/musician David Mellor checks out what the PC can do.

Recording engineer/musician David Mellor puts the 16-input version of Soundtracs' new mixer range through its paces.

One problem with living in the centre of London is that unless you are a zillionaire you can only afford something small. So when you return from doing the laundry run and find a large crate monopolising the main living area of your flat, you start to wonder why you agreed to do a mixer review in the first place!

The reason is, of course, that it's fun to try out the latest in technology - even if it does occupy your only table and force you to write the article on an upturned cardboard box.

So what has this mixer got that most other mixers haven't? The answer is MIDI. Okay, it's not in the same class as MasterMix or Total Recall as far as desk automation goes, but in small studio terms it is a big step forward. Before we get into that aspect, however, I think we ought to see how the Soundtracs PC works as a conventional mixer. I must stress before I begin that I take the view that in an ideal world everything would be perfect, so any criticisms I make are from that standpoint and if I 'made allowances' for any reason then what I write would be worthless. It is up to the manufacturer how he trades facilities and performance with price, and up to the user to decide what compromises he is prepared to accept. Whatever standard you are working to, from Portastudio to Air Monserrat, it is impossible to have everything you want. Please sigh now!

I was fortunate that my wiring loom is very similar to that required for the PC, so I was able to connect it to my patchbay with only a little extra lead making. Don Larking Audio Sales were good enough to lend me the machine for some three weeks, so I was really able to get to grips with it and find out what it can do, what it can't do, and what it can do with a little head-scratching.

The Soundtracs PC is an in-line design. This may be a personal view, but in my dictionary of synonyms, 'inline' means the same as 'awkward'. There is something so sensible to me about having a channel section and a separate monitor section on a mixer.

My idea of heaven would be to have around 16 input channels for recording and as many monitoring inputs as tracks on the tape recorder, with each monitor input available for use on mixdown and having the same facilities (EQ, Aux sends etc) as the main channels. Until someone makes one (please, please, please) then I shall just have to pine.

The benefit of an in-line design is that the desk can be less wide, which is definitely a good thing. The channel modules therefore have to be made longer to accommodate the extra monitoring section, but the normal suitcase-and-bricks exercises will soon lengthen the arms sufficiently! On the PC, I think Soundtracs have done a good job of making the in-line system reasonably easy for the brain to cope with, although a few minor quibbles remain.


I do like the method of construction, given that an enclosed module with rigid backplane system would have been prohibitively expensive. Everything on the channel, including the inputs and outputs, is mounted on a long steel strip. The connectors are hidden from view by the meter bridge. The advantage here is that there is no need to wire the channel to connectors mounted on the chassis of the mixer - which would increase the cost and could cause reliability problems. You do, however, have to remove the meter bridge before you can take out a channel for inspection - and there are quite a number of screws, so it is not a job for mid-session.

Internally, the channel modules were of a high standard of construction, using four ICs and 11 transistors. All connections to the channels are made via two ribbon cables which have enough slack to let you pull a module up and detach it easily. This is not the case in some mixers I have come across, where you have to remove a couple of modules from one end, unscrew several others and shunt them along until you have enough slack cable to disconnect the one you want! Mixers contain a lot of fault-prone components such as pots and switches and it is a big plus if maintenance can be made easy. The use of ribbon cable was not found to cause crosstalk problems, as it does in some other designs. (The PC boasts a crosstalk figure of 80dB between channels.)

At the top of each channel is an electronically balanced microphone input with switchable phantom power. Mic inputs are all fairly similar these days and there were no noise problems I could detect. I was a little less happy about the line input which works by attenuating the input signal then feeding it to the mic amp. Although I did not take measurements, there is something wrong to me about throwing away some of your perfectly good signal and then beefing up what is left. It does save components though, and I could not hear anything amiss.

One clever feature is that all line inputs are on stereo jack sockets and by connecting either the 'tip' or the 'ring' you can use 0dBu or -10dBu equipment at their correct levels. I could not, however, find any indication in the manual of which way round it was, nor from the circuit diagram which did not identify component values.

There is a switchable -20dB pad to take care of unusually high output from mics. Other connections to the module are the insert points and the multitrack input and output.

Moving down the module, there is a competent four-band EQ section with two mid sweeps (50Hz-1kHz, 500Hz-10kHz) and the important in/out switch. Very good it was two, especially the high frequency control (12kHz) which some designers make heavy weather of.

Next is the auxiliary send section. This just happens to be one of my hobby-horses. I find it so useful to have a pre/post-fade switch for each send that I cannot understand why mid-priced equipment manufacturers do not provide them. The usual convention is to have one switch shared between two sends, which is great if you only happen to be using one of them! Compromising in this way assumes how you are going to use the mixer, when you probably do not even know how you are going to use it yourself until the moment you desperately need the facility. I hope Soundtracs and other manufacturers will take note because I am trying to make a serious point. The arrangement on the PC is Aux 1&2 switchable as a pair, Aux 3&4 dedicated post-fade (pre-fade selectable internally).

Output selection is another tricky point. The PC model I had for review was the 16 input version, but my comments will apply to other types. In brief, channels 1-8 can only be routed to outputs 1-8, channels 9-16 only to outputs 9-16. In other words, inputs and outputs work in blocks of eight. You can get round the problem with a patch cord or two, but I have never been in a situation where I have not been able to route to any channel of the multitrack straight from the desk. I'm getting that 'thin end of the wedge' feeling and I don't like it.

There is also a button-saving arrangement of output selector switches (total saving: one button per channel) which means that you can only route to four outputs at the same time. That's not really important because it's not meant to be a theatre desk, and there are no group level controls anyway, but I would have liked that extra button.

Apart from the peak LED, mute and solo buttons, that just about completes the channel section - but I should tell you how it works.

Being an in-line desk, the returns from the multitrack recorder are available on channel-strip mounted level controls. This is the Record mode of operation of the desk. Press a button and you are in Mix mode, when the multitrack outputs are connected to the channel input and the monitor input is freed for use as an effects return, extra input or whatever. In this way, the number of inputs is doubled on mixdown so your 16 channel desk now has 32 inputs. Now comes the clever bit!

There is a button marked 'Split' in the EQ section. What this does is to assign the high frequency (12kHz) and low frequency (50Hz) EQ controls to the monitor input and leave both mid sweeps active in the channel. So, if you are mixing you may have, for instance, track one of the multitrack on channel one with some mid frequency EQ, and use the monitor as an echo return with a little top rolled off. This to me is a completely different kettle of fish to the cheese-paring done to save on switches. (This clever machine mixes metaphors as well!!) Sensible use of resources is what I would call it, and although I would like a load of channels with full EQ, I may not be in a position to pay for it. A definite OK from me here. Same goes for the auxiliary sends. Aux 1&2 and 3&4 can be switched in pairs between channel and monitor (although I wish they could be switched separately).

The centre module of the Soundtracs PC mixer contains the Aux masters, talkback, oscillator and monitor controls. The Aux masters are as you would expect them although curiously enough, where every other solo button has a green LED, these do not. There is a solo 'active' indicator on the LED meter bridge, however, and a handy solo level knob.

Sorry chaps, I can't pass on this next one. The oscillator is combined with the talkback facility. So what? Well, how about an oscillator which can be routed to the studio speakers? (Ouch!) How about a talkback mic that cannot be sent directly to the stereo machine for slate purposes? How about an oscillator that cannot be routed directly to the stereo machine for head tones? And can we have a button for each frequency please (50Hz, 500Hz, 1kHz, 10kHz)?

I feel awful about having to make all these criticisms, because what Soundtracs have done is to go out on a limb and to produce a mixer that is different to all the rest, rather than give us yet another common-or-garden console. I do not doubt for a moment that Soundtracs could take any point have made and put a figure in pounds on how much extra it would cost to have things as I would wish. Never mind, here comes the really good bit...


I had better say right from the start that there are no moving faders, no VCAs and no automation on the desk. What you do get is MIDI-controlled muting. Every channel, monitor, and auxiliary send can be muted as necessary in time with the track by your own MIDI sequencer. This is a powerful facility.

In the centre module of the mixer is a 9-button panel which is used to control all the MIDI functions. There are two numerical displays, one telling you the internal patch number and the other, on the meter bridge, the MIDI channel selected. There are five MIDI sockets on the back of the mixer - one MIDI In and four which are internally selectable between MIDI Out and MIDI Thru. Two modes of operation are available: 'internal' and 'external'. Internal mode is where a MIDI sequencer is used to directly control the mixer and any ancillary devices. In external mode the mixer can initiate program changes on MIDI reverb units and the like, and although you can still use a sequencer, you would probably only use external mode if you wanted to control those changes manually.

One of the biggest problems with multitrack recording of any standard is noise. Each time you double the number of tracks on your tape recorder or channels on the mixer, you add 3dB's worth of noise - even if you use a noise reduction system. How nice it is then to be able to mute channels when they are not making any contribution to the mix. I hate having to do it manually because it is a purely mechanical function and generally adds no 'artistic' control to the mixing process. It is so much better though to have 'clean' sounding mixes than the mush you get when you don't do it.


After thrashing about with a soldering iron for an hour or so to finish wiring up the PC, I set to work mixing a track by a little-known band, Topless Airlines, titled 'I Married A Gorilla' and featuring the glamorous Lisa Webb on vocals. (It's my band by the way - you have to get the plug in somewhere!)

I had seven tracks on the tape plus sync code and 'live' contributions from an Akai S900 sampler and DX7. (An even livier contribution came from a mic in a real echo chamber - the bathroom.) The tape tracks were a bit on the messy side with unwanted passages that needed removing but were too tight to erase on the tape. I could have mixed in sections but it is so much better to work with a continuous piece of music. On the PC, muting can be done in two ways. Either by 'playing' the mutes into a sequencer in real time, button presses being recorded as MIDI note on/off information, or by storing 'patches' of mutes into the mixer's own memory and then recording these as program changes into the sequencer.

Playing the mutes into the sequencer may seem the most intuitive way of doing it - you could do it from a keyboard - but there is a snag. The 16-channel Soundtracs PC has 36 mutable signal paths. It is a strong possibility that your sequencer cannot handle more than 16 simultaneous note on/off messages on a particular MIDI channel, therefore problem! One way out is to use the MIDI Split function on the mixer. This spreads the information over four MIDI channels (hence the need for the four MIDI Outs mentioned earlier). I found it simpler to setup patch changes.

The PC can store 100 patches - which are simply combinations of mutes. I went through the song a few times and noted down patches for each section and set up eleven different ones. It was quite simple to record these changes into the sequencer from my DX7 and thereafter the machinery looked after itself. It was quite gratifying to see different combinations of mute LEDs come on during the song, ending with 'mute all except reverb return'. (I think that one may become a standard.) Once I had set this up, I was free to concentrate on level changes.


From the ridiculous to the more sensible, I spent the rest of my time with the PC mixer doing library music tracks, and I must say that I love the MIDI function so much that I shall find it very hard to go back to my old-fashioned manual mixer. I say old-fashioned and I mean it. I am not in the market for a new desk at the moment, but I might be soon, and after using the PC there is no way now that I would consider a non-MIDI console for my own home use.

As a commercial studio user it is a slightly different matter, because it is not me who is going to have to run around doing all the muting, so it probably would not affect me in choosing which studio to book.

If you are looking for a new mixer then the choice is up to you, but whatever desk you are thinking about, you should take a good look at this one because, at least in this section of the market, the Soundtracs PC MIDI mixer represents the future.

Prices of the PC MIDI Series mixer are: 16-input version £4045 (£4651.75 inc VAT); 24-input version £5250 (£6037.50 inc VAT).

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Sound On Sound - Copyright: SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.


Sound On Sound - Feb 1987

Gear in this article:

Mixer > Soundtracs > PC MIDI Series

Review by David Mellor

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