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Understanding the DX7 (Part 2) | |
Article from Electronics & Music Maker, May 1984 |
The second part of Jay Chapman's guided tour through the Yamaha DX labyrinth, with an in-depth analysis of one of the factory-programmed voices.
Jay Chapman begins his in-depth look at how the DX keyboards generate their sounds by examining one of the factory-programmed voices — 'E. Organ 1'.
Voice ROM1 A17
If you have never downloaded any of the ROM voices into the DX7 internal memory (thereby overwriting the latter) you can simply press the green INTERNAL keypad (under the MEMORY SELECT legend) followed by the green '17' keypad, to call up this particular voice. Check the display:
Straight away we can see that this voice does not use any frequency modulation, as all six operators connect directly to the horizontal line (below the operators) which represents the output. The string of '1's in the display tells us which operators are actually in use and as we have a complete string of ones, ie. '111111', we know that all six are turned on. In fact we have six 'carrier' operators - they all contribute directly to the sound we hear.
OK, lets start some experimental keypad pushing.
The first thing to do is examine the sound that each carrier is producing. To do this, turn all the operators off by pressing the green keypads '1' through '6'. The display should change to '000000'. Now turn on one carrier at a time by pressing the green keypad bearing the relevant Operator's number, and play a few notes. When you want to move onto the next Operator, press the same keypad again to 'toggle' the current Operator off. Your display of ones and zeros should cycle through the sequence '100000', '010000', '001000', '000100', '000010' and '000001' as you listen to each Operator in turn.
With the exception of Operator 6, you should hear a simple sinewave, of a different pitch for each Operator, which is turned on and off by the keyboard acting simply as a switch, with no hint of any envelope shaping. Thinking back to the 'drawbar organ' discussion in last month's introduction this state of affairs is not at all surprising, but don't be fooled, there is a little subtlety to be uncovered yet.
We know already that to create the timbre of a sound we must use frequency modulation and/or combine frequencies that are (usually) harmonically related. Since we do not have any modulating operators in use in this instance, we should look for what frequencies are being combined. To do this, simply press the green FREQUENCY COARSE keypad and turn all the Operators back on ('111111'). The display will not show the actual frequency of the Operator unless the operator is in Fixed Frequency mode (see last month's article). For most 'musical' sounds, Frequency Ratio mode is chosen so that the pitch output by the Operator is related to the keyboard note played and thereby indirectly to the frequency of other Operators also in Frequency Ratio mode - this is the case for all the Operators used in 'E. ORGAN 1'.
By pressing the purple OPERATOR SELECT keypad you can cycle through all the Operators displaying their frequency ratios. This is what you should find:
As we have two pairs of Operators beating in this manner, we have two low frequency waves weaving in and out of each other which makes the overall effect less clinical and more ethereal (very subjective comment that last one!). As a last point on this detuning business, note that all the Operators are detuned slightly relative to each other, thus heading toward that good old Hammond tone-wheel sound, albeit from a completely different angle of approach!
The last, but by no means least, item on the agenda for 'E. ORGAN 1' is Operator 6 which has a very important job to do. Turn all the Operators except 6 off and play a note on the keyboard. You will hear a short burst of sound which is fairly percussive. The pitch of the sound is one octave and a fifth above the keyboard pitch played (frequency ratio 3.00) and it is the combination of percussiveness and a more piercing pitch that adds some 'bite' to 'E. ORGAN 1', emulating the famous Hammond 'key-click'.
The percussive effect is governed by the Operator's envelope generator which we will look at next. Make sure Operator 6 is turned on and selected, then press the RATE keypad under the EG legend (the keypad is green and has '21' on it). If you have just Operator 6 on, your display should look like:
It's not too difficult to see why Operator 6's output comes and goes rather sharpish!
Well, that's quite enough time spent on just one voice... next month we'll move on to something a little more complex that shows off more of the DX7 features.
Readers may be interested to know that an introductory booklet on the DX synthesisers entitled 'Getting Started' and compiled by Dave Bristow is available free of charge from Yamaha. Just write to Martin Tenant, Yamaha Musical Instruments, (Contact Details), enclosing a stamped addressed envelope.
Read the next part in this series:
Understanding the DX7 (Part 3)
(EMM Jun 84)
All parts in this series:
Part 1 | Part 2 (Viewing) | Part 3 | Part 4 | Part 5 | Part 6 | Part 7
All About Additive (Part 1) |
Patchwork |
Fun in the Waves (Part 1) |
Dave Bristow on the Yamaha DX7 - Yamaha DX Keyboards |
Hands On: Yamaha DX7 |
A Handy Way To Solve Sticky Control Problems |
The Ins and Outs of Digital Design |
Hands On: Korg M1 |
Modular Synthesis - Producing String Sounds (Part 1) |
Advanced Music Synthesis - Inside the Yamaha GS1 & GS2 |
Rock Around the Clock |
The Sensuous Envelope Follower |
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Feature by Jay Chapman
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