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Advanced MIDI Amiga Sampler

Got an Amiga? Want a sampler? Then cast your beady eye over this one. Greg Truckell is your guide.

The idea of using a computer as a sampler is not really a new one, more of an old one recently revisited with some new ideas. The best of those ideas is quite a simple one: wouldn't it be handy if your computer could be your sampler and your sequencer at the same time? We're not talking Fairlight power here - but then we're not talking Fairlight prices either. AMAS retails for just under £100 - that's another of the better new ideas about sampling. AMAS itself can't do your sequencing, but if your Amiga sequencing software allows you to trigger the Amiga's internal samples (eg. programs like Dr.T's MRS and Microillusions' Music X) then your Amiga can become your sampler and your sequencer.

AMAS is only one of a number of sampling peripherals available for the Commodore Amiga. I can't swear that it's the best, because I haven't used them all. I have, on the other hand, used a range of conventional samplers, from the Mirage to the S1000, as well as some Atari ST peripheral samplers, and I must say that AMAS compares very well.


The Commodore Amiga has four sound channels. This enables two-note polyphonic stereo sample playback or four-note polyphonic mono sample playback. Not a lot of notes either way, but still enough to compare reasonably with the likes of an Akai S700 at six monophonic voices. Let's talk about multitimbral operation...

AMAS stores samples in banks of 200K. A bank may contain up to 10 stereo samples, dividing the 200K however you require. Bearing in mind that the software itself occupies around 200K of RAM, this gives you one bank on a half megabyte computer (A500), three banks to a one megabyte machine (A2000 or A501 expanded A500), and a whopping great eight banks maximum - 80 stereo samples - on a two megabyte machine (expanded A500/2000).

There is no need to stick to stereo sampling - many instruments make more sense in mono. Furthermore, mono samples can be combined to create stereo effects from initially disparate elements. While it should be obvious, remember that stereo samples take up twice the memory of mono samples of the same length and sampling frequency.


The Amiga, as anyone who hasn't had their ears filled with buns for the past couple of years will tell you, is a multitasking computer - so that must make AMAS a multitasking sampler, right? Well, sort of.

Sadly, due to limitations of the current Amiga operating system (called Workbench) itself - not of anyone's software - playable samples can only be held in the bottom half megabyte of memory. This more or less rules out multitasking with sampling. It doesn't rule out multitasking with samples, however, which can be stored as IFF files and used within any compatible software - such as Music X. Both 3-voice and 5-voice IFF save options (on AMAS V1.3) are available for Aegis Sonix and Deluxe Music Construction Set. Multitasking (or the lack thereof) is also a problem likely to be resolved in the future with Commodore's proposed new Workbench release; Version 1.4 will apparently overcome the problem, and the next AMAS revision will, I am told, be fully multitasking. This will enable you to run sampling and sequencing software simultaneously, co-resident on the Amiga.


Measuring in at around 130 x 110 x 40mm, the AMAS hardware interface sits nicely on top of your A500 (A2000 owners will have to find some suitable space, and there is a different hardware version required for the less common A1000). A couple of blobs of highly expensive universal computer peripheral adhesive (Blu-Tack!) will ensure it doesn't fall off every time you hit the Amiga's Function keys.

The interface itself has no buttons or switches, and draws its power from the Amiga. It connects via both the serial and parallel ports, which could be a nuisance if you usually have a printer hooked up. AMAS will operate as a sample editor and playback unit even with the sampling hardware disconnected, so if there are instances where you absolutely must have sample editing and free serial and/or parallel ports, then AMAS still meets your requirements.

Audio inputs are via a stereo pair of phono sockets (quoted 0.8 volts sensitivity - just about right for mixer auxiliaries) or a single 3.5mm socket (25 millivolts sensitivity - too sensitive even for electric guitar pickups). The interface features twin Butterworth filters, and has approximate maximum sampling frequencies of 40kHz and 90kHz in stereo and mono respectively.

AMAS itself only uses the MIDI In connection. The presence of the additional MIDI Out and Thru may seem a little odd, until you realise that AMAS is the only MIDI interface you need for your Amiga MIDI software. Rather a nice touch, I thought - and it makes even more sense when you consider the multitasking possibilities. If you are using AMAS hooked up to audio and MIDI patchbays, then you can simply plug it in and forget about the hardware, although the restrictively short length of the ribbon connectors means that AMAS will never be very far away from you.


Supplied on a single 3.5" floppy disk, the AMAS software autoboots to the program's main screen (V1.3 can be run from the Workbench). A passing Atari ST samplist was heard to comment that AMAS appeared to be powerful, effective, and looked good. The point, apparently, was that if something was that powerful and effective on the ST then it would look awful. I suspect he was right; AMAS has the sort of hi-tech graphic front end you normally associate with deep space combat simulators. Thankfully, getting the most out of AMAS is easier than learning to fly the Martian Rebel S1000 on instruments.

Having connected AMAS to a sound source, such as a CD or cassette player, or the auxiliary send/returns of a mixer, it will be obvious when something is happening. At the first trace of a signal of adequate level, the stereo oscilloscopes (left and right) will spring into life. Meters flash bright green with louder signals, yellow with over-loud signals, which can also be seen when the signals on the scopes square off. Signal attenuation can only take place at source, as AMAS has no input level controls of its own. This probably means that you won't be able to sample directly from a CD player - you'll have to route the CD through your mixer.

The right input can be directed to the real-time spectrum analyser which, when activated, freezes the oscilloscopes. The spectrum analyser then appears above the left and right sample displays, at the top of the screen, and performs the dancing Manhattan skyline routine in lovely sync with your input signal. The oscilloscopes are pretty good considering their small on-screen dimensions. Using the higher resolution of the Commodore 1084S colour monitor, I was able to faithfully reproduce the operator waveforms from a Yamaha TX81Z synth. It is possible to magnify either or both oscilloscopes, perhaps to analyse quiet decays.

A full complement of editing facilities is available, including the standard cut, paste, insert, delete, copy, mix, reverse, and fade in/out. What is not so standard about these features is that they are so very easy to use. Try executing a cut, paste and fade out on an Ensoniq Mirage from the front panel, and see how you feel. With AMAS, these functions are so obvious that the handbook becomes almost superfluous. Come to think of it, the handbook is probably best skimmed through and ignored for your first few sessions - you learn more from actually using AMAS than you do from reading about it. Due to the graphic mouse-driven user interface, messing around doesn't just scratch the surface, it gives you access to the most powerful functions available within AMAS.


Sampling itself is very simple. First define your sampling frequency, either in Hertz (Hz) or as the periodic value of the Amiga's DMA timer. Define the area of memory to be sampled into as left or right, mono or stereo, and as the area between the markers, pointers, or the whole bank. Click on Record to start sampling immediately, or activate the Auto function, which enables you to set a recording threshold on the graticules which appear over the oscilloscopes. Once sampling begins, the screen blacks out and the sample will be heard from the Amiga as It is made. If you want to preview the sound before sampling it, then activate the Listen button to hear what the source would sound like at the sampling frequency selected.

Looping is a mixed bag of pros and cons. The editing facilities, combined with the ability to magnify the sample editing screens, make smooth loops much easier to find. There is, however, no facility for the looped portion to be anything other than the whole sample; there can be no attack transient before the loop. Enveloping is simple, too - there isn't any! However, enveloping of IFF samples is available on Music X, so all is far from lost.

There are some less standard editing features to be found on AMAS, including volume up/down, sample shrink, filter, stereo 'bounce', and channel swap. A little explanation is in order...

Volume up/down serves best to normalise samples; that is, to slightly boost the playback level of samples which are fine except that they are too quiet and don't exploit the full dynamic range. Having said that, using volume up/down will not alter the dynamic resolution of your samples. Volume up/down could also be put to good use with a multi-sampled drum/percussion kit, where some fine tuning may be required in order to create the desired balance of the various instruments.

Sample shrink (described on the packaging as sample shrink/stretch, but in fact lacking any stretch facility) can be used to compress a sample by 25%, 50% or 75%. The handbook points out that a 10kHz sample squeezed by 50% to a 5kHz sample will sound better than a sample made at 5kHz, because the sample was made at a higher frequency and is therefore less subject to aliasing. This is, roughly, true: any aliasing effects avoided by sampling at 10kHz will not manifest themselves even after squeezing. However, any aliasing still present at 10kHz would theoretically be almost twice as bad after squeezing to 5kHz. AMAS gets around this, and improves the quality of compressed samples, by using an averaging process during squeezing. Since the only limitation is the 200K bank size, it would seem to be a good idea to make all your samples at maximum sampling frequency in the first instance, and then to see how much sample shrinking they can survive if they have to.

Filtering is rather more complex than the brief mention it receives in the handbook might lead you to believe. Filtering is possible at 75%, 50%, or 25%. At 50%, for example, it digitally filters off frequencies in the sample above 50% of the Nyquist frequency (the Nyquist frequency is half the sampling frequency). Filtering is set for 6dB/octave roll-off, which might seem pretty nigh useless were it not for the fact that it can be repeated as often as you like, and it operates very quickly - a full 200K sample bank can be filtered in a few seconds. A full 24dB/octave lowpass filter is obtained by filtering the sample four times.

Stereo bounce can operate on mono or stereo samples, enhancing the stereo imaging of both. Sample information within the area defined by the pointers can be crossfaded from one side of the stereo image to the other, over the playback time within the pointers. The results can either be copied over or mixed with the original data. The graphic representation of this edit is particularly effective: the area between the pointers on the left sample screen becomes defined within a rectangular box. The proportions and direction of the bounce are controlled by two numeric displays for either end of the box, which, when edited by clicking on increment/decrement buttons in the alert box, cause the edit box to become trapezoidal across the right sample screen, graphically indicating the effects of the edit.

Having defined an area within the pointers. Mix allows you to then select a mix direction (L to R, R to L, or from one or both banks to the same bank(s). Having done this, the pointers remain as boxes, which can be dragged or scrolled to a new location, into which the data from the original location will be overlaid (the sample is folded in with the sample data already present).


Before you can replay your samples (other than from the on-screen Play button), you have to place them into programmable locations. For Amiga keyboard response, the 10 Function keys can be used to trigger playback of the samples in a bank. The labels F1-F10 serve as the program numbers for MIDI playback also. When 'Prog' is selected, followed by a selection from F1-F10, the samples' pointers, markers, stereo mode, loop flags, window magnification and sample frequency are all saved to the chosen Function key.

Triggering sample playback from a MIDI keyboard is a fairly simple matter. Having programmed your samples, select a MIDI channel and go. Don't expect miracles over MIDI, though. Simple note information is all that AMAS understands and responds to, over a range of -1 to +2 octaves. There's no pitch bend, modulation, aftertouch or even velocity response. Well, what do you expect for under a hundred quid - an S1000?

Keyboard splits you might not have expected, but they are easy to set up. Working from left to right up the keyboard, select your initial program (F1-F10), then the split P key, followed by the F key for the program above the split. The system now waits for a key to be pressed on the attached MIDI keyboard, which becomes the split point. Multiple splits are equally easy to define - just repeat the process. Banks of samples created in this fashion can be saved to disk in raw form (not as IFF files) and will reload as banks with all parameters set as saved. Pitch-shifted playback without a MIDI keyboard is also possible from the Amiga's alphanumeric keyboard, as well as from the Function keys.


Updates to AMAS are already in the pipeline, and are primarily concerned with improving the bank addressing capabilities. Sadly, there are not likely to be any Fast Fourier Transform analysis capabilities in the next revision - apparently, someone did the dirty with the relevant software routines and included them in someone else's program. It's hell out there...

Thanks to software like AMAS, the musical future of the Amiga looks rosy. As an entry-level system offering the user potential for growth without having to discard outgrown equipment, a package based around an Amiga A500, AMAS, and Music X looks hard to beat. Add an A501 half megabyte RAM expansion and a MIDI keyboard such as a K1 or D5, or even a humble DX100 or CZ101, and we are still talking about just over a grand for the complete system. Several companies used to make 8-bit samplers that cost an awful lot more. AMAS may not be a Fairlight, but for total ease of use and effective facilities it has a lot going for it. The people's CMI is here at last.


£99 inc VAT.

Microdeal, (Contact Details).

Also featuring gear in this article

A Hell of AMAS
(MIC Jun 89)

Browse category: Software: Sampler > Microdeal

Next article in this issue

Making The Most Of Your Kawai K1

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 1990

Donated & scanned by: Mike Gorman


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Review by Greg Truckell

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