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Powertran MCS-1 Sound Sampler & Delay Line


Sound sampling and MIDI are today's two most desired features it would seem, and this MIDI Controlled Sampler from Powertran embodies both.


The news from Frankfurt is that sound sampling is at last within reach for those of us with more modest incomes, provided our bank managers are of an understanding disposition, of course! But although there promises to be new, more affordable products from such names as Akai and Korg retailing around £1100, there has been an exciting and reasonably priced British product available to the home recordist for some months now. A sampling machine that you can add to an existing MIDI-based system, which enables you to play samples from keyboards equipped with CV and Gate as well as MIDI, is marketed by Powertran.

Some of you may own, indeed have built, one of Powertran's previous products, such as their DDL, because they are all available in kit form. If you feel you can't cope with the 'Airfix' approach, however, and your soldering is as bad as mine, parting with more cash will make Powertran happy to build it for you.

Description



The MCS-1 is a digital sound sampler and delay line housed in a 2U 19 inch rack-mounting metal case. As a delay it has most of the usual features: vibrato, phasing, flanging, ADT, and echo, with a maximum delay of 32 seconds, allowing you to make a sound, run off and make a cup of tea, then run back into the studio in time to hear the repeat which, unfortunately, will sound like you are hearing it through a trawlerman's sock because of the reduced bandwidth at this length of delay. Bypass and infinite Freeze are two other functions that the MCS-1 has in common with more conventional delays.

On the sampling side, memory size is variable from 8 bytes to 64 Kbytes, giving a storage time at a 32kHz sampling rate of 2 seconds, and 8 seconds at 8kHz. Audio bandwidth is variable from 12kHz to 300Hz and the unit achieves a dynamic range of 72dB with an eight-bit companding system.

For controlling the MCS-1, the MIDI system has an advantage over the one volt per octave (CV) control range, which is only effective up to two octaves, while the MIDI control will play over five octaves. One of the options available for the MCS-1 is the ability to store and recall sampled sounds digitally on floppy disk via a special interface and a BBC micro, putting it a step ahead of the competition but adding extra cost.

Controls



The MCS-1 has an attractive grey front panel with clearly labelled rotary controls, 24 illuminated and colour coded switches, and a red digital display of the parameters. There is plenty of space for the controls, making it both more attractive and easier to operate. Audio In and Out connections are made via standard ¼" jacks on the front panel, although Audio Out is also available on the rear panel. Two black pushbutton switches select low or high levels and attenuation of zero or 20dB. To the left of the front panel we find four grey rotary pots labelled Level, Repeat, Mix, and Tune.

The Level control operates on the input signal in conjunction with the overload light (labelled 'clip'). Repeat is self-explanatory; Mix alters the proportion of direct signal in relation to the output of the delay line, although I'd prefer to have seen separate direct and delay controls as I find that when in use as a delay line the overall volume is affected when you start mixing in the delay - and this holds true of the standard Powertran DDL too. Tune is a fine overall pitch control.

Above the attractive MCS-1 logo, which is a real improvement on the usual Powertran legend, is the large, four digit, red LED display showing parameter values and MIDI information dependant on which you wish to see. This display is easy to read, but I can't think why they haven't included the far more practical option of a display calibrated in milliseconds when the unit is being used as a normal DDL, because it is very difficult to think of things in terms of bytes when you are trying to set up a delay. To the right of the unit is the infinite turn rotary Controller for incrementing or decrementing parameter values which can be up to 50 steps a revolution, dependant upon which parameter and sensitivity (coarse, medium, or fine) you are using.

Switches



Nearly all of the right-hand side of the panel is taken up by the twenty four selector switches colour-coded in light and dark grey, blue, red, and orange. Once again Powertran have managed to combine attractiveness with practicality of design and each of the switches has its own clearly visible red LED which illuminates when the pushbutton is selected.

Arranged in two rows of twelve, top left we find the Freeze button which will operate manually only in Delay Line mode and in conjunction with the Freeze input on the rear panel. As with more conventional delays, this enables you to prevent any further data being written into the unit's memory, so that any sound already in there is frozen. However, if Voice mode is selected the Freeze LED indicates when recording is in progress by remaining off while recording is actually taking place, but illuminating once the sound has been stored in the memory.

Click Track activates the MCS-1 's onboard metronome, which will superimpose up to 16 beats onto the audio output, dictated by the memory length - the shorter the length, the smaller the number of clicks produced. As a timing guide for sample duration it can prove useful if you, for instance, wanted to play a sequence of notes and loop them into a continuous pattern.

Delay Line and Voice mode mentioned above are the master controls for delay and sampling operation. When Delay Line is selected the unit reads and writes continuously from memory, and in this mode can be used for all the usual DDL effects like flanging, ADT, echo etc. However, the sounds can be transferred to Voice mode operation in which their pitch and duration can be played from a connected keyboard.

The red Record button comes into play when sampling in Voice mode, its LED flashing when selected, indicating that the MCS-1 is ready to start recording which it will do when given an audio signal or when the Record button is selected for a second time. Once in record, its LED will be continuously illuminated while the Freeze LED is off, and when recording is complete the Freeze LED illuminates and the Record button light goes off - easy isn't it! The stored sound can then be replayed using a keyboard, or by selecting the grey Play switch which will play through the sample once each time you hit the button.

BBC Interface



The BBC and Down Load buttons enable you to store your sounds on floppy disk via the BBC micro and the MCS-1's interface box. Clearly marked, the interface box sports four connections. Via the MCS-1 connector, 64K bytes of sound storage plus loop points are exchanged. Up to six sounds can be stored on an 80 track double-sided disc, but you'll only get one sound on a single sided 40 track disk - the transfer time being approximately 40 seconds per sound. Power to the interface is also supplied through this connection. The MIDI In connector enters MIDI codes into the BBC and a MIDI Thru connector duplicates the MIDI In data. MIDI codes generated by the BBC are output by the MIDI Out connector and the interface itself is connected to the BBC micro by a 34 way ribbon cable via the 1MHz bus interface. In fact, the whole process of linking Sound Sampler & Delay Dine up the MCS-1 to the micro is quickly and easily achieved and a Data LED illuminates when serial data enters the interface.

Noise Reduction



A switch is available to introduce noise reduction which effectively cuts out the quantisation noise that accompanies certain types of samples. This is an encode/decode system that does not affect the bandwidth.

Working with the spin wheel Controller on the far right of the unit, there are three switches to adjust the sensitivity over which the parameters are adjusted: coarse, medium, and fine.

Starting left to right on the bottom row of switches, we have the Sample Speed selector, which changes the rate at which the memory clocks through and operates in Delay Line mode. This speed is expressed as a variable number with a value between 128 and 4095 where 128 is a fast sample speed and 4095 a slow one. Both Sample Speed and Ram Size parameter values are indicated on the central display, RAM Size being zero to 6553 when selected. Both are modified using the Controller to the right of the front panel.

I must admit that I found this concept a little hard to grasp at first because there is no easy way of relating this number to delay time or sample length. Although the readout is not calibrated in any units, it does give some indication of how much of the memory is being used. Between the two you have absolute control of the memory and can change it one byte at a time, which is significant when you come to looping samples and wish to find the point that gives you the least glitch. Bypass works in the same way as normal digital delays by routing the input signal to the audio output unchanged.

Control Keyboard



There are two switches, both serving dual purposes for keyboard control when the MCS-1 is in Voice mode. The first switch, when lit, is for Gate control. However, you have the option of two Gate modes - one which turns off abruptly, and another which has a longer decay tail indicated by a display of S for short, and L for long decay. If this button is not illuminated then the sound can be triggered, but although this means that it is triggered by the gate signal it will play itself to the end of the memory. Also, only a gated signal may be put through a looping process.

The second switch selects whether MIDI (lit), or CV connections will relay pitch information. However, pitch, sound duration, pitch bend and vibrato, are all controllable via MIDI, and the notes played are indicated on the LED display in MIDI code. When this button is switched on the MCS-1's MIDI channel number will automatically default to MIDI channel one, but any of the sixteen MIDI channels may be selected by rotating the Controller whilst holding down the MIDI channel selector button.

An alternative way of changing the sample speed is available using the Pitch Shift, which will alter the sample speed values in semitone increments (using the spin wheel Controller) between 12 (low end), and 80 (high end).

Looping



Two switches govern the looping of a sampled sound to achieve a continuous note: Loop Start, which defines the point in the memory where you want your loop to start, and Loop Length, which determines the point at which the loop 'jumps back' to its start. Glitch-free looping is not an easy thing to achieve with a continuous sound like a vocal "ah". First you have to choose a suitable point for your loop to start, then make your loop length a complete number of cycles (by trial and error) to produce a continuous note that is glitch-free.This is best optimised using the Fine control setting and the correct point is obvious once you find it.

Four remaining controls operate with the MCS-1's internal tracking filters and sweep oscillator. Filter Shift allows the filters to be offset by an octave less or greater than the system sample speed and the chosen figure is displayed as a number between 0 and 12. This filter cut-off frequency may be offset so that the operator may use his discretion in deciding what kind of filtering is necessary for a particular sound eg. a snare drum, which is a sound containing a lot of natural noise, may be filtered less heavily resulting in a brighter sound without compromising the subjective sound quality. On the other hand, a bass guitar has a small proportion of high frequency harmonics and so more care must be exercised in choosing a suitable cut-off frequency to avoid digital noise becoming audible during the sample by bringing down the filter. Experimentation soon makes it clear how to get the best from this valuable feature Sweep Range is a level control for the oscillator's sinewave modulation with a display between zero and 100, while Sweep Speed has the same numeric range and both are altered using the Controller and their master on/off switches.

Rear Panel



This contains the non-illuminating power switch, Audio Out, Freeze In, CV and gate ¼" jack sockets. The Gate needs a TTL (+4V) signal to generate a command and can be used either in conjunction with the CV socket for control via a one volt per octave keyboard, or on its own receiving a trigger from a drum unit.

MIDI In and Out (there is no MIDI Thru), and the BBC In/Out sockets accept five-pin DIN connectors to link them with the custom designed interface unit for the micro. Master, Slave, and Serial Bus multiway connecting points, although in situ, are intended for future options.

In Use



For delay purposes the best quality is obtained by using the fastest sample speed and altering the RAM size which will then give you a delay of 2 seconds at a bandwidth of 12kHz. For longer delays you have to sacrifice bandwidth but practice will enable you to choose the best quality of delay by picking the right RAM size and sample speed.

Flange, chorus, and ADT effects are all of a high quality. At the fastest sampling speed, increasing the RAM size by one digit will increase the delay by less than one millisecond. As you can imagine, with such control you can obtain a wide range of effects.

Sampling a sound is a straightforward procedure, but you have to be careful not to give the machine too much input level otherwise you get an audible 'click' at the beginning of the sample. Sound quality was very good especially when using the noise reduction, although you may not need to use it for something like a snare drum. Triggering was accurate when using both MIDI, and CV and Gate, while note tracking using MIDI was good up to the very top end of a keyboard which sounded slightly out of tune. However, tracking using CV and Gate is only true over about one and a half octaves, the bottom semitone or two sounding distinctly suspect.

When you sample a sound (be it a kitchen utensil, a belch, or an orchestral chord), it will appear at middle C when using a MIDI keyboard. Playing above this note raises the pitch of your sound (also shortening the sample), while playing below this note lowers the pitch and lengthens the sample much in the same way as using the varispeed on a tape machine. However, you can only tune your sample to the nearest semitone (using the Fine tune control) when the MCS-1 is receiving pitch information via MIDI or CV. This means that unless the pitch of your sample is near middle C, the notes you are playing on the keyboard won't be the same as the resultant pitch of the sample. But this doesn't cause problems in practice and when you are not controlling pitch from MIDI or CV and Gate, the MCS-1 gives you complete control. Playback of samples is purely monophonic and on MIDI keyboards it's best to set them to Mono mode purely to overcome any lazy playing technique.

Conclusion



Powertran have a very good product on their hands here, and it's a shame that the MCS-1 has not had the exposure it deserves over the past few months. Unfortunately, because of its recent increase in price it will eventually be in competition with the new products coming out of Japan later this year like the Akai S612 which is offering six-voice polyphonic sampling for nearly the same price although it does not have the sample storage facility via the BBC micro nor the delay line. If you're used to the concept of displays in milliseconds then the MCS-1 design philosophy of RAM Size and Sample Speed may initially cause confusion, but it's a concept that soon becomes familiar. It was a shame I had to give it back really.

An excellent demo cassette is available for the unit costing £2.50 plus VAT. The ready-built MCS-1 sells for £849 plus VAT but if you are prepared to invest the time, the Kit version costs only £599 plus VAT. Available only from Powertran Cybernetics Ltd., (Contact Details).



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AKG D321 Dynamic Microphone


Home & Studio Recording - Copyright: Music Maker Publications (UK), Future Publishing.

 

Home & Studio Recording - Apr 1985

Donated & scanned by: Mike Gorman

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Sampler > Powertran > MCS-1

Review by John Harris

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