Tony Hastings offers more hints and tips designed to help owners of the popular Ensoniq Mirage expand their sampling skills.

Welcome to the second part in the series about everyday sampling folk down on the farm. For those of you lucky enough to have read Part 1, you will know that I am attempting to pass on some of the accumulated tips and hints that I have picked up in using my Mirage and talking to other Mirage owners all over the world.

Last month I talked specifically about One-Page Loops and also how to have 15 different sounds available 'instantly' without having to load from disk. This time I am going to concentrate on several different tips rather than just one main item.

CONFIGURATION PAGE

I'm sure that you all know how to save samples (and their subsequent variations) to disk, probably even any sequences you might choose to use as well, but for some unknown reason Mirage users rarely think about saving configuration parameters to disk.

Configuration parameters encompass such things as 'Master Tune' and, most importantly, MIDI information.

We are all well aware that to 'boot' the Mirage from cold we have to use the latest OS software, and that this contains the information necessary to use the machine. These days many keyboard players have multiple set-ups with each instrument having a different MIDI channel number and status. Whenever the Mirage is booted up, it always sets itself to OMNI ON and MIDI Channel 1. But not everyone wants their Mirage to be set this way (especially those who own the Multi-Sampler expander version). In fact, it is often the case that people will use the same MIDI channel set-up for their instruments all the time (notably in sequencer situations). So, wouldn't it be nice to have the Mirage boot up with all your desired MIDI configurations ready from the word go?

'How' you ask. Easy... set everything to the way you want it. Take the most recent Operating System disk you have (it should be version 3.2) and remove its 'memory protect' tab. Then, simply press parameter Mon the Mirage and everything you have set up will be stored and remembered on the disk. Don't forget to put the memory protect tab back in place, though. Now, every time you boot up with that disk you will get your new MIDI values installed automatically.

MORE MEMORY!!

It's a shame how quickly we become spoiled by technology. I remember my girlfriend buying me a ZX81 for Christmas one year (not that long ago).

I sat down and played with it for hours on end and she became one of the first 'computer widows'. I happily programmed away desperately trying to fill up the massive 16K of memory that was at my disposal. Not long after that I saw a Commodore 64. Insane!! Here was a machine with 64K of memory and sound generation facilities and colour and only(!) costing about £500. How could anyone want for more than that?

Yet here I am only a few years down the technological road, typing this very article on an Atari 1040ST with one megabyte of memory, and already I'm getting itchy fingers for the new Atari with two megabytes of memory and a blitter chip (oh yes, there's a 20 megabyte hard disk I fancy as well). I suppose it's only human to want more all the time. Mind you, manufacturers have a lot to answer for. No sooner have you spent three months looking at what's available, arranged a second mortgage, pawned your dog and finally bought the damned equipment, than out comes something bigger, better, faster, flashier and cheaper.

I often get asked if the Mirage can have more memory added to it to make it more powerful, along the lines of the Akai S900 with its 750K's worth. Well, the short answer is NO, although the longer answer is YES (and not just because of the amount of letters in each word!).

'No'... because the Mirage is designed to operate with only 64K of memory on each keyboard half (there are 256 pages each containing 256 samples, which equals 64,000 bytes approximately). To add memory you would have to completely re-write the operating system which would make this newly-expanded Mirage (and its samples) incompatible with older generation Mirages, and it would then end up being a different machine altogether.

'Yes'... because there is a Canadian company currently developing software (and hardware) that will give you 512K of storage memory. They claim that it will allow your Mirage to have four complete Upper and Lower keyboard set-ups available at the touch of a button. By all accounts it will come in kit form and you will need to install it yourself or get an engineer to do it for you. It should be fairly easy to fit but be warned that doing so will probably invalidate any guarantee that you might have. Me? Well I think it's worth losing my guarantee for the flexibility it would give me in a live performance situation. In the meantime, the company are keen to see how many people are interested in the idea before they put it firmly into production. So, if you feel it's a great idea, why not write to them with words of encouragement and see what they say?

Their address is: Mirage Upgrades, 2004 Fernwood Road, Victoria, British Columbia, Canada V8T2Y9. Oops! I forgot to mention that the price of the kit should be somewhere around $300-$400 dollars.

CLEAN HIGH FREQUENCIES

The following little dodge was discovered by J. William Mauchly who is the senior software engineer at Ensoniq itself. As you will see, it is only useful for certain applications, but in the right context the technique can produce very high quality, high frequency samples. The main consideration for this method is that the sample you are about to work on is not going to be transposed, so suitable sounds would be really crisp, 'clean' cymbals, and special effects, etc.

OK. You all know about 'aliasing' don't you? Yes, it's that nasty problem whereby high frequency 'noise' is reproduced in the lower part of the audio spectrum and consequently is impossible to remove with the standard low-pass filter (ie. a filter that lets the low frequencies through but shuts out the upper ones). The only way is to make sure that you are sampling at a sample input rate that is less than half the sample input frequency. Suffice to say that in many cases the samples you take can sound muffled because the filters which cut out the aliasing also dull the sound. Not only that, aside from aliasing, there is sometimes another type of noise present in the sample called 'table look-up noise'.

Table look-up noise is usually more apparent in the upper octaves of a sample because the Mirage has a rather strange way of replaying its samples. When you play a sample an octave above the 'note' at which the sample was originally taken, the Mirage replays every other sample. And if you play it an octave above that, then it skips to every fourth sample, and soon. By the time you get to the very high octaves the sound can be quite noisy because there aren't many samples actually being heard, and so the noise in between samples becomes more and more obvious.

One way to lessen this problem is to use the Mirage's 'Input Sampling Filter' which allows you to take up to 50,000 samples per second as opposed to the normal 33,000 samples. Thus with more samples to start with, even when some are 'skipped' there are still enough to produce an accurate and reasonably quiet sound.

Here's where this other technique comes into play. You can try the following out yourself or attempt to imagine what I am describing.

Take a sample of a fairly pure sine wave about 2 or 3 octaves above middle C and make sure that the 'Sample Time Adjust' parameter is set to a value of 34. Now if you play the sample back you will hear a good example of the 'aliasing' effect, where another sine wave is being played at the same time but at a lower frequency. This lower sine wave moves around from note to note and although it sounds random, it is in fact following a strict rule.

As you transpose the sound closer and closer to the original pitch, the alias gets lower in pitch. That's great, so by doing this enough will it eventually go away? Well, by finding the note on the keyboard where the alias note is at its lowest pitch, and using the 'Fine Tune' control (38), you can cause the aliasing frequency to go sub-audio ie. drop below about 20Hz. Having done that, however, another problem arises. Although you can no longer hear the aliasing frequency itself, it is still having an effect on the original sample, since it is now behaving like an LFO (low frequency oscillator) and causing vibrato and tremolo effects.

The only way to get the aliasing frequency and its unpleasant effect to go away completely is to reduce the tuning of the alias to exactly 0 Hz. Alas, life isn't as simple as all that! The tuning of the Mirage (being an 8-bit machine) is done in 256th of an octave steps and there is no such step that corresponds exactly to 0 Hz - and close isn't good enough I'm afraid!

This is where the aforementioned Mr Mauchly's 'trick' works. By copying the sample to Oscillator 2, you can use the 'De-tune' parameter (33) to lower the frequency of the alias even more. This works because the increments used in the 'De-tune' operation of Oscillator 2 are much finer than the ones in the 'Fine Tune' mode.

If you set the 'Mix' parameter (34) to a value of 63, you will only hear Oscillator 2 and can then slowly detune until you hit 0 Hz and the alias disappears - entirely!!

In effect, what you are doing is setting the playback sample rate of the sound so that it exactly matches the sampling rate of the 'Q' chip. Good stuff eh?

To go over the major points again:

A. You must sample your sound using a sample time of 34.

B. The 'Mix' control (34) must be set to 63.

C. The 'De-tune' on Oscillator 2 should be set to a value of 1 (although other variations may work).

D. You must set the 'FineTune' according to the following table, depending on what musical key you want the sound to come back on:

KEY	FINETUNE [68]
C	4E
A	8E
D#	CE
F#	0E

To ascertain the correct value for other notes you should experiment a bit. You should also set the octave by ear.

SWAP SHOP

Well that's it for this issue. I hope that some of the points covered here will prove of value to you as you discover the delights of sampling on the Mirage. If you have any useful tips that you've discovered, whether basic or complex, do send them into me and I'll try to incorporate them within future articles. Bye for now.

For readers interested in joining 'Oasis', the newly-formed and officially recognised UK Mirage Users Group, the address to write to is as follows: (Contact Details).