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Cheetah SX16

Sampling Module

After much pre-publicity, Cheetah's first venture into the world of samplers is here. It's 16-bit stereo, reads S900 disks and is reviewed by Vic Lennard.

Noted for producing the sort of gear musicians want for the sort of money most musicians have, Cheetah have just unveiled their first sampler - no less than 16 bits for no more than £800.

AFTER A SHAKY start, Cheetah are starting to build a strong reputation for producing workmanlike equipment at very attractive prices. Their MS6 analogue synth expander, MD16 drum machine and MQ8 sequencer were never intended to be the last word in hi-tech sophistication. Instead they were intended to make essential pieces of equipment available to those of us on a tight budget - a job they all do admirably.

With the SX16, Cheetah are venturing into the sampler market. The advance of technology has led to a decrease in price of the analogue-to-digital converters (ADC) and their output, digital-to-analogue (DAC) counterparts and given Cheetah the opportunity to produce a 16-bit stereo sampler for just under £800. No, it's not April.

The SX16 is a stereo, 16-bit sampler with a maximum sampling frequency of 48kHz and 512 KBytes onboard memory (expandable to 2Meg). The basic unit will give a sampling time of 2.7 seconds at maximum frequency. Up to eight voices can be played back simultaneously and it will respond to note data on any MIDI channel. There are eight individual, polyphonic outputs and up to 16 samples can be held in memory at any one time.

The sampler is a 19-inch, 1U-high rack-mounting module in industry-standard black. The front panel has four main attributes; a 2 x 16 character, backlit LCD; a double-sided, double-density disk drive as standard; 23 push buttons which are used for both selecting/setting parameters and naming samples and a 9-pin joystick port and phono modulator output for direct connection to a television. Not to mention a mains switch.

The rear panel has the relevant quarter-inch jack sockets (two input, eight output) and MIDI In, Out and Thru ports. An RS232 port is provided for future expansion and a 6-pin DIN socket handles the power - this reduces the need for internal screening and almost eliminates internal heating.

Unfortunately, the cable connecting the psu to the SX16 is only one metre long, which means that you can't place the unit very high in a rack. A contrast control on the LCD would also have been useful as you can only see clearly head-on to the display. Bearing in mind the length of the psu cable, this could cause problems.


ON POWER UP, the SX16 checks its disk drive before coming up with a Ready prompt on screen. The Operating System is in internal ROM, not disk-loaded. This means that updates will probably require the replacement of ROMs, but reduces the boot-up time.

There are various ways that manufacturers have used to call up parameters for editing - Akai have push-button menus and a control wheel while Casio use a slider. Cheetah have gone for a parameter number system. You type in the number of the relevant parameter that you wish to edit, type the new value and press Enter. To this end, all letters (upper case), numbers and necessary symbols are available from the front panel buttons. These are split into two sets in red and blue with the Sample button doubling as a shift button to select one set or the other.

To select a parameter, either press Parameter followed by the required number, or key in the number. A list of all parameters is provided in the manual and in keeping with the simplicity of design, this list is currently pretty short; 16 sampling and 19 global parameters.

There are three methods of altering parameters: the single arrow keys increase or decrease the value by one and scroll if you hold them down; the double arrow keys jump in steps proportional to the time between each press; use BS (backspace) to clear the current value and enter your own. Some neat ideas here. Too many manufacturers forget about the fact that humans are basically impatient and don't want to wait 20 seconds while a display motors from 1 to 1,000.

Certain parameters have specific default values. Sampling Frequency (Parameter 3) always defaults to 48kHz, although there are seven options available; 48kHz, 32kHz, 24kHz, 16kHz, 12kHz, 8kHz and 6kHz. Output defaults to socket 1, MIDI Channel to 1 and so on. These cannot be changed - you don't get the option to save a default set of values to disk.

Taking a sample is very straightforward. Hit Select followed by one of the two New options (for Mono or Stereo), type in the name of the new sample and set the length. This is in millisecond units and defaults to the maximum available from the unused memory. Hitting Sample now tells you which input(s) are being used (1 for Mono, 1&2 for Stereo) and displays the level of the incoming signal as a 15-segment horizontal bar. Without any kind of gain control, there's no way of adjusting the incoming audio level to the SX16. Cheetah have taken this option to cut down on a pre-amp stage, so keeping cost down and reducing input noise. This means that the accuracy of the meter has to be relied upon for lack of distortion in the sampled signal. Although the manual doesn't say so, it appears to be OK to go up to the 12th segment of the meter on a continuous signal, but not beyond. Dynamic sounds can even peak as high as the 14th segment. Apart from the slight increase in background hiss on playback, the fidelity of the monitored sound is very good, making it easy to take good samples. Anyone with a Casio FZ sampler will appreciate what happens when this is not the case (see review MT, March 1990).

While the input cannot be adjusted, the monitor output can. Parameter 24 allows you to set a value which is a percentage of the output. So setting 50% will give you half of the nominal volume.

To sample, you press any button. The SX16 goes into trigger mode and starts sampling as soon as the trigger threshold is exceeded. This can be adjusted by parameter 23 from 0% which will start sampling immediately a button is pressed, to 100% which will need the peak of an explosion to set it off. A value around 2% or 3% picks up the attack of a bass drum but the degree of noise at the input will dictate how low you can go. The display tells you that you are "Sampling" and returns you to the display showing the name of the sample at the end of the sampling time. Press Play to hear the result. I have to admit that in my experience with samplers, it is difficult to think of any which are as easy to use as the SX16 in terms of the basic taking of a sample.

With the first sample in memory, pressing Clear removes it from playback but not from memory. This lets you take the next sample by following the previous procedure again. Let's say that you want to delete one of the samples: "Select" that sample by scrolling through the names and press Clear. The screen then asks you whether you want to "1:Rename 2:Delete 3:Cancel" on the top line. How can this be shown within 16 characters? The display scrolls. Excellent idea.

"Cheetah have realised that Mirage users will be likely purchasers of SX16s and have incorporated the software for a Mirage MIDI sample dump - a welcome first."

If your first sample was titled Gorby then selecting option 2 asks you "Are you sure you want to delete Gorby? - 1:0K 2:Cancel". This is close to being idiot-proof. The single- and double-arrow keys can again be used to scroll through faster or move immediately to the end of the message (useful once you know your way around the machine).

The SX16 has a unique method for managing its memory. Imagine that your naming procedure has not been all it should have been and that you delete the wrong sample. The SX16 doesn't clear that sample from memory until you re-use the sampling space. Consequently you can go through the process of naming a new sample and setting the length and your previous sample will re-appear. If the length you set is different from the original then you either get hiss at the end or a cut-down version.


SAMPLERS CAN BE used for a variety of purposes, one of which is to emulate a natural instrument. As the memory space of any sampler is restricted, looping is used where a portion of the sample is played over and over again to give the aural illusion of a continual sound.

Selecting parameter 11 puts the SX16 into loop mode and the sound starts to continuously play back. The single/double arrows are then used for fine/coarse alterations to the start and end points of the loop depending on whether you press the Strt or End buttons. The screen changes to "Loop set: Start/End" although no numbers are displayed on screen to show you where you are. This means that you have to rely solely on your ears (could be another first if you're an A&R man).

Most samplers use crossfade looping to create glitch-free loops. This takes a small portion of the sample before the start of the loop, copies it and mixes it into the sample before the end of the loop. The length of the portion is usually variable, with small portions being used for the removal of slight glitches. The lack of this option on the SX16 will make smooth loops difficult to obtain. Akai's S700 had a "preset" version which worked at the twist of a knob and the difference was quite stunning in terms of loop continuity. I'd have liked Cheetah to have offered a basic version such as this on the SX16.

A process called truncation is used to cut away unwanted bits from a sample. Parameter 12 sets the sample into looping mode and the start and end points are adjusted, after which Enter permanently deletes the parts of the sample outside of what is being heard. This is a little awkward when working with short samples such as bass drums, where it's difficult to decide whether there is a gap or part of the end of the sample is being cut off. You can always exit truncate mode, listen to the sample and re-enter for any fine adjustments.


LET'S SAY THAT you've sampled a snare drum with plenty of reverb. There's every chance that you'll want to change the dynamics of the sound. Gating the reverb is no problem - simply truncate the sample. But what happens if you want to shorten the sample and still have it sounding natural? Parameter 1 affects the release time; a value of 0 will give no release time, 1 plays the entire sample while 2 up to 200 places a release time on the sample, with higher values releasing quicker. This parameter is independent per sample, but affects both halves of a stereo sample.

You can change the playback pitch of a sound by altering parameter 2. This sets the original pitch and gives you a numerical as well as a note value - for instance, 60 (C4). The numbering system is the same as Roland's.

The response of a connected MIDI keyboard is an unknown quantity and so Cheetah have offered seven different velocity response curves for each sample; fixed velocity where no matter how hard you press the key, the velocity is taken to be 64; linear velocity where the sound volume is directly proportional to the key velocity; reverse linear so that higher velocity gives lower volume and vice versa; exponential curve; reverse exponential; logarithmic and reverse logarithmic. The effect of these is explained quite well in the manual and should let you create any feel that you want. The three pairings of normal and reverse curves are also useful for velocity crossfading samples. As you can select any two samples to make a stereo pair, and the velocity sensitivity acts separately on each of them, you can create one sample fading in as the other fades out. A similar facility is offered for aftertouch response.

A low-frequency oscillator (LFO) is also available. Depth as a percentage figure of the maximum and Modulation rate from 1 to 400 (0.1Hz-40Hz) can be set for each sample using parameters 13 and 14.


WITH UP TO 16 samples in memory, the next step is to place them across the keyboard. You may have a selection of drum sounds or a set of multisamples to assign to different notes. It's here that a degree of confusion is likely to creep in.

Parameter 6 selects the MIDI channel you wish to assign to a sample. Any note on this channel will play this sample. Parameter 27 is the Global MIDI channel and will play all samples assigned to splits, on this channel. The global MIDI channel, or that for any sample, can be set to zero, removing any sample or the splits from MIDI control. This effectively means that you can only have one program of keysplits in memory at any one time.

Parameter 26 puts the SX16 into split keyboard mode. The display shows "Split: choose 1", at which point you select one of the samples in memory. Pressing a key on a connected MIDI keyboard (say, C5) will then show "Set on C5" - play a second note while holding down the first (say, F5) and this changes to "Set on C5-F5" for a range of notes. You then have the option of assigning either the second half of a stereo pair to the same split or another sample altogether. This may have been given a reverse velocity sensitivity as mentioned before. If one of the splits which you set up overlaps a previous one, it will steal that part of the range from the other split. So, any note on a keyboard can play back a maximum of two samples.

"In my experience of samplers, it is difficult to think of any which are as easy to use as the SX16 in terms of the basic taking of a sample."

While assigning samples to splits, you also have the option to transpose the pitch of the samples so that they play back correctly within that split. This doesn't affect any transpose value that you may have set under parameter 10 for individual samples.

Although the outputs are polyphonic, playing a note a second time before the sample assigned to this note has died out will silence the first note. There are a variety of times when this is not an advantage, like when a ride cymbal is being played. Parameter 37 lets the first note continue its natural course and will continue to add notes up to the limit of the polyphony setting.


AS EITHER A DD or HD (quad density) disk drive can be fitted to the SX16, the formatting procedure takes this into account and asks you which type of formatting is in order. Don't try to cheat and format a disk to quad density when the drive is only a double density version - the SX16 will have none of it. Each disk can be named and given a sequence number. This is because the entire memory from an expanded SX16 won't fit onto a single disk. The sequence number will tell you whether disks are being loaded back in the right order.

You can either save the entire internal memory including all samples and parameters (ALL) or individual mono samples with their own parameters, by selection. The screen displays how much is to be saved and how far through the process it is, in Kbytes for the entire memory and milliseconds for individual samples. This means that if you save the entire memory, you can no longer load individual samples from within the block. When loading, "*" before the name signifies an ALL file.

Cheetah have realised that the most popular family of samplers to date is Akai's S900/950/1000 and have implemented the necessary software to read the disks (again paying attention to the disk density in the case of the S1000). The SX16 scans the disk and reports on everything that is found including the "fixups" protection file and programs, which it cannot load. All samples are then shown along with their size in Kbytes.

Disk loading on the review model SX16 was very slow - a 4.5 second S1000 sample disk took over five minutes to load. Happily, Cheetah acknowledged the problem from the start and have since released improved software that significantly reduces loading times. They reckon this brings the SX16 in line with other samplers currently on the market. Unfortunately I wasn't able to put their claims to the test, but as the company themselves were never happy with the performance of the disk drive, it suggests they will have dealt with the problem properly.

Failure to correct this problem shouldn't present studio users with any insurmountable problems, but it is going to make changing disks for live work rather impractical. As it stands, however, any improvement over the performance of the review model will be most welcome.


SO MUCH FOR facilities, what does the SX16 sound like?

To make 16-bit technology available at this kind of price, shortcuts have to be taken. One shortcut Cheetah have made is to cut the number of DACs. Instead of one per voice, several voices share a DAC, using a technique called time slicing. The result is that the precision of playback is not as good as it would be with one DAC per voice.

The SX16 offers a variety of playback modes; 8-voice, 4-voice, 4-voice filtered and 2-voice filtered. The lower the polyphony, the better the playback characteristics. The filtered modes take some of the harshness away from the top end. At 48kHz, the playback accuracy is pretty good but by the time you get to 32kHz, top end loss is quite noticeable. Sampling rates below this are of limited use. Indeed, even the bass samples on the factory disk are recorded at 48kHz.

Loading samples from an S900 disk and comparing playback with an S900 (a 12-bit sampler), shows this lack of definition clearly. Downloading the samples from both machines into Genwave (a sample editor) and comparing the frequency/time graphs of the waveforms showed them to be identical - which puts the deterioration down to the output stage of the SX16. A similar result occurred when identical samples were taken on both machines. Why compare with the S900? Because the RRP of the SX16 puts it at the same position in the market as a secondhand S900.

This isn't a criticism - to be honest, the SX16's quality was higher than I'd expected, and in the context of four-track recording, would be quite acceptable.

However, this isn't the end of the story. One feature which impressed me was the clarity of samples when played back below their sampled note. Having got used to the response of the Akai S900/950, I was most surprised to find that samples were still clear one or two octaves down. You can also change the playback frequency to any value between 1kHz-99kHz to fine tune the pitch of a sample, although the length changes proportionately. This differs from the Transpose option (parameter 10) which works via MIDI. The SX16 accurately reproduces stereo samples image-wise - no mean feat.

"Having got used to the response of the Akai S900/950, I was most surprised to find that SX16 samples were still clear one or two octaves down."


THE SX16 WILL respond to MIDI messages in all MIDI modes including mode 4 (for use with guitar synths and sequencers). It will also recognise MIDI patch changes for selection of the individual samples in memory, pitchbend, MIDI volume and sustain pedal. However, for some inexplicable reason, it won't respond to MIDI modulation wheel messages. This defeats much of the benefit of having an LFO controllable in this manner.

Cheetah have also realised that many Ensoniq Mirage users will be likely purchasers of SX16s. To this end, they have incorporated the software for a Mirage MIDI sample dump - a welcome first to my knowledge. If the sample being obtained from the Mirage is too long to fit into memory, then it's truncated; if it's too short, the rest of the space is left unfilled. A message informs you which of these has occurred.

The MIDI sample dump standard facilitates transfer of samples between suitably-specified samplers. Unfortunately, the SX16 will not respond to a sample dump request. This makes life tricky when dumping to software of a similarly limited nature. It is possible, but the timing required in pressing the button on the SX16 and the mouse button for the computer is tight. The SX16 will receive samples from other samplers by the same method.

Apart from being able to play a sample forwards using the Play button, you can also play it backwards by pressing the left-hand single arrow button. When you press the right-hand arrow button it puts the SX16 into Scratch mode - where you can play a sample forwards by moving the pitchbend wheel on a connected MIDI keyboard to the right and backwards by moving it to the left. The further you move the wheel, the faster the sample plays. The result is as close to scratching a record as is possible without using a turntable. Perhaps this gives an idea as to which market the SX16 is aimed at.


WITH 512K MEMORY as standard, the sampling time on the SX16 is short. Cheetah are selling a 2 Megabyte version tor £1399 - £600 for an extra 1.5 Meg of memory, which seems pretty steep. Third party 2Meg upgrades for the Akai S1000 are currently around £300.

The disk drive can be replaced by a high-density version, which will save twice as much data per disk, for £150 plus £15 fitting charge.

Finally all editing, including sample waveforms, can be displayed on a TV and altered using a joystick. The internal card costs about £150 and a joystick a further £25. I couldn't test this out, but my comments regarding the lack of info on the display could be solved by using this.


YOU'VE PROBABLY NOTICED that no comparison at all has been made between the SX16 and any other 16-bit sampler. Such comparisons would be pointless bearing in mind that at the price, the SX16 is not intended to be a competitor to the likes of the Akai S1000.

Many of the features on the SX16 have, however, been very carefully thought out. In use, the buttons and the scrolling display are very user-friendly, and the average musician should only need the manual to check the parameter numbers. Looping samples for hip hop and house music is easy and the various velocity curves make cross-fading of one sound to another simple to implement.

Stereo sampling can allow you to achieve results which you will only have dreamed of with a mono sampler. Polyphonic outputs and access to most other samplers either by disk reading or sample dumping - there are many very good aspects to this unit.

On the down side, the SX16's sound quality is poor when used in 8-voice mode - Cheetah obviously appreciate this, however, as the SX16 defaults to four-voice filtered mode. Running in four-voice mode restricts you to either four mono or two stereo samples simultaneously. In other words, the combination of sound quality and polyphony works against you.

A little bit of me can't help but wonder what an extra £100 on the asking price would have done to the sound quality. Still, if you're a first-time buyer or considering upgrading from a Mirage or one of the samplers using quickdisks, the SX16 is well worth a listen - be prepared to place your order, pay your deposit and join the queue.

Price £799.95 including VAT.

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Life Of A Prophet

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Corea Man

Music Technology - Copyright: Music Maker Publications (UK), Future Publishing.


Music Technology - Aug 1990

Gear in this article:

Sampler > Cheetah > SX16

Gear Tags:

16-Bit Sampler

Review by Vic Lennard

Previous article in this issue:

> Life Of A Prophet

Next article in this issue:

> Corea Man

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