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Exercises

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probonopd edited this page Jul 15, 2022 · 27 revisions

🔶 This page is a work in progress. Contributions are appreciated.

Preface

The DX7 and other similar instruments have been percived as "difficult", and many musicians have used them mainly to play preconfigured voices that came on cartridges or, later, in .syx files. While you can do the same with MiniDexed, you really should learn how Frequency Modulation (FM) synthesis works in order to unlock the full potential of the instrument.

This page is meant as a supplement to the 1986 book "The Complete DX7" by Howard Massey and explains how to do the exercises found in the book using MiniDexed. It is assumed that this is covered by "Fair Use", this page does not replicate content from the book but merely explains how MiniDexed can be used to produce comparable results.

Prerequisites

While for playing it is desirable to have multiple Tone Generator (TG) instances and sound effects, this is not desirable for learning how Frequency Modulation (FM) synthesis works. Hence, all of the exercises use only one Tone Generator (TG) instance, which equals to one DX7 instrument. All exercises also assume no effects to be present, like on the DX7 instrument. To perform any of the exercises, prepare MiniDexed like this:

  • Rename performance.ini on the SD card so that it doesn't get loaded. This results in a default setup with only one Tone Generator (TG) instance and no effects being active
  • If you later want the default performance settings with multiple TG instances and effects, you can rename the file to performance.ini to enable it again.

Conventions

These conventions are used to make the instructions more readable:

  • Menu items are bold
  • Parameter values are italic

Chapter 1: Basic Audio Theory

The basic theory applies today just like it did 4 decades ago.

Chapter 2: The Menu

Unlike the DX7 instrument 4 decades ago, MiniDexed uses a menu structure like found on many devices. This means that MiniDexed just has one knob that also acts as a clickable button, and does not need the many buttons found on the DX7 instrument. Hence, the descriptions regarding the buttons on the DX7 do not apply to MiniDexed, but all buttons have equivalents in the MiniDexed menu.

This is how you operate it:

  • Rotate the knob to select items and to adjust parameters. Whenever you can rotate the knob to the right, you will see -> on the screen. Likewise, whenever you can rotate the knob to the left, you will see <- on the screen
  • Click to open a submenu
  • Long-press to leave a submenu

Once you have learned the basic menu navigation, we can use the following notation to describe how to navigate anywhere in the menu structure: MiniDexed -> TG1 -> Voice

This means that on the MiniDexed start screen (which you see when switching on MiniDexed), you select TG1 (which is selected by default), then click to open it, then select Voice (which is the default), then click to open it.

If you are asked to open another menu item in the same submenu, e.g., MiniDexed -> TG1 -> Detune then you long-press to to go out of Voice where you were before, then rotate the knob to select Detune, then click to open it.

Note that a long-press brings you one layer back, e.g, from Open MiniDexed -> TG1 -> Voice to Open MiniDexed -> TG1 from where you can select Voice and click to open MiniDexed -> TG1 -> Voice.

Exercise 1: Playing a voice

  1. Open MiniDexed -> TG1 -> Voice (this is the parameter you are editing)
  2. Rotate the knob to select one of the voices
  3. Observe that the display shows the number and the name of the sound you have selected
  4. Play notes on the keyboard. You hear the sound of the selected voice
  5. Rotate the knob to select other voices

Exercise 2: Does not apply

This exercise does not apply to MiniDexed because there is no concept of built-in memory versus cartridges. All voices are stored on the SD card.

Exercise 3: Editing a voice

  1. Select any random voice like in exercise 1
  2. Play notes on the keyboard. You hear the sound of the selected voice
  3. Now remove the SD card
  4. Play notes again. The sound is still there even though you removed the SD card

Exercise 4: Adjusting the tuning

  1. Select any random voice like in exercise 1
  2. Open MiniDexed -> TG1 -> Detune (this is the parameter you are editing)
  3. Turn the knob while you are playing a note on the keyboard and listen to the change in pitch. Then play a chord. Notice that the pitch of all notes changes the same amount
  4. Select a different voice like in exercise 1. Play notes on the keyboard. The pitch is changed in the same way, because changing the Detune parameter is not voice-specific

Exercise 5: Key transposition

  1. Select the E.PIANO 1 voice like in exercise 1
  2. Play a scale on the keyboard to confirm you hear an electric piano sound
  3. Open MiniDexed -> TG1 -> Edit Voice -> Transpose
  4. Note that the bottom line says C3
  5. Rotate the knob to the right to select D3
  6. Play the same scale on the keyboard again and note that the whole sound is now one note higher, as it has been transposed by one full note
  7. Repeat: Rotate the knob to select another amount of transposition, then play the same scale on the keyboard again

Chapter 3: The Operator

Chapter 4: Voice Initialization

Exercise 6: Loading INIT VOICE

Note that you can select INIT VOICE voices from any bank that has no sounds in it.

  1. Open MiniDexed -> TG1 -> Bank
  2. Turn the knob right until you have selected a bank called NO NAME
  3. Open MiniDexed -> TG1 -> Voice
  4. Turn the knob right until you have selected a voice called INIT VOICE

Exercise 7: Changing the Algorithm

  1. Load INIT VOICE like in exercise 6
  2. Open MiniDexed -> TG1 -> Edit Voice -> Algorithm
  3. Turn the knob left until you have selected algorithm 1
  4. Play a note and keep the key pressed while you make further changes to the algorithm by turning the knob. The sound should not change pitch or timbre

Exercise 8: Enabling and Disabling Operators

  1. Open MiniDexed -> TG1 -> Edit Voice -> OP1 -> Enable
  2. Turn the knob left until you have selected Off
  3. Play a few notes
  4. Turn the knob right until you have selected On
  5. Play a few notes
  6. Repeat the steps above with for OP2,...6 to affect the other operators. You can use the following SHORTCUT to get there quickly: While the first line of the display still says Enable OP1, press the knob and rotate it to the right while keeping it pressed until the display says Enable OP2. Now release the knob. You can now change the value for Operator 2. Repeat for the other operators

Exercise 9: Listening to Individual Operators

  1. Load INIT VOICE like in exercise 6
  2. Open MiniDexed -> TG1 -> Edit Voice -> OP1 -> Enable
  3. Verify that the value is On, which is the default
  4. Play a few notes
  5. Turn the knob left until you have selected Off
  6. Open MiniDexed -> TG1 -> Edit Voice -> OP2 -> Enable. You can use the following SHORTCUT to get there quickly: While the first line of the display still says Enable OP1, press the knob and rotate it to the right while keeping it pressed until the display says Enable OP2. Now release the knob
  7. Turn the knob right until you have selected On
  8. Play a few notes again. There will be no sound!
  9. Also listen to the other operators individually in the same way

Exercise 10: Output Level

  1. Load INIT VOICE like in exercise 6
  2. Open MiniDexed -> TG1 -> Edit Voice -> OP1 -> Output Level
  3. Notice that the value is 99, which is the default value for Operator 1
  4. Play a few notes and listen to the volume
  5. Turn the knob left until you have selected 85. Output Level of operator 1 is now at 85
  6. Play a few notes and notice that the volume is lower than before
  7. While playing a note, turn the knob further left until you have selected 0
  8. Play a few notes and note that the volume is lower than before
  9. Notice that the volume continued to become lower and lower until there was no sound anymore
  10. Open MiniDexed -> TG1 -> Edit Voice -> OP2 -> Output Level. You can use the following SHORTCUT to get there quickly: While the first line of the display still says Output Level OP1, press the knob and rotate it to the right while keeping it pressed until the display says Output Level OP2. Now release the knob
  11. Notice that the value is 0, which is the default value for operator 2
  12. Check the Output Level value for operator 3 in the same way
  13. Notice that the value is also 0, which is the default value for operator 3 as well

Note that unlike on the original DX7 instruments, you hear output level changes in real time, that is without having to play another note.

Chapter 5: The Carrier

Exercise 11: Pitch Default Values

  1. Load INIT VOICE like in exercise 6
  2. Open MiniDexed -> TG1 -> Edit Voice -> OP1 -> Freq Coarse
  3. Notice that the value is 1, which is the default value
  4. Open MiniDexed -> TG1 -> Edit Voice -> OP1 -> Freq Fine
  5. Notice that the value is 1, which is the default value
  6. Open MiniDexed -> TG1 -> Edit Voice -> OP1 -> Osc Detune
  7. Notice that the value is 0, which is the default value

Exercise 12: Frequency Coarse

  1. Load INIT VOICE like in exercise 6
  2. Open MiniDexed -> TG1 -> Edit Voice -> Algorithm
  3. Rotate the knob to select 32
  4. Open MiniDexed -> TG1 -> Edit Voice -> OP1 -> Freq Coarse
  5. Notice that the default value is 1
  6. Play a note
  7. Rotate the knob to select 2
  8. Play the same note again and notice that the tones are now one octave higher
  9. Rotate the knob to select 3
  10. Play the same note again and notice that the tones are now one musical fifth higher
  11. Play the same note again and while still playing the note, rotate the knob to the right until you reach the maximum value, 31
  12. Play the same note again and while still playing the note, rotate the knob to the left until you reach 1

Exercise 13: Additive Synthesis

  1. Load INIT VOICE like in exercise 6
  2. Enable operator 2 and set its Output Level to 99 similar to exercises 8 and 10
  3. Open MiniDexed -> TG1 -> Edit Voice -> OP2 -> Freq Coarse
  4. Notice that the default value is 1
  5. Play a note
  6. Rotate the knob to select 2
  7. Play the same note again. You should hear two sine waves playing together one octave apart from each other
  8. ...

🔶 TODO: To be continued. The remainder of this page is a skeleton structure. if you have followed the book and the exercises until here, you should be able to figure out how to do the rest of the exercises on your own. Feel free to edit this page and fill in the details, matching the style of the earlier exercises.

Exercise 14: Frequency Fine

Exercise 15: Beating Effects

Exercise 16: Detune

Exercise 17: Fixed Mode

Chapter 6: The Modulator

Exercise 18: Making Sawtooth Waves

Exercise 19: Making Square Waves

Exercise 20: Making Pulse Waves

Exercise 21: Changing Pitch

Exercise 22: Complex Timbres

Exercise 23: Non-musical Timbres

Exercise 24: Detune in Systems

Exercise 25: Beating with Complex Timbres

Exercise 26: Detuning Algorithm 20

Exercise 27: Repetitive Pitch Change

Exercise 28: Dissonant Effects

Exercise 29: Animating Sounds

Exercise 30: Brightening E.PIANO 1

Exercise 31: Adding Chorusing

Chapter 7: Stacks and Feedback

Exercise 32: Sawtooth Waves as Modulators

Exercise 33: Square Waves as Modulators

Exercise 34: Feedback

Exercise 34: White Noise

Chapter 8: Saving

🔶 Note that saving modified voices is not implemented in MiniDexed yet. In the meantime, edit voices on a computer and save them as `.syx' files instead, e.g., using the Dexed software.

Chapter 9: Envelope Generators

Exercise 43: Default Values

Exercise 44: Model EG

Exercise 45: Rate 1

Exercise 46: Rate 4

Exercise 47: Level 1

Chapter 10: Low Frequency Oscillator

Chapter 11: EG and Keyboard Bias

Chapter 12: Keyboard Level Scaling

Chapter 13: Function Controls

Note that this chapter does not apply to MiniDexed.

Chapter 14: MIDI

Note that MiniDexed can receive MIDI over USB, over 3.3V Serial, over Mini-DIN MIDI attached to USB using a MIDI-to-USB adapter, and over a Mini-DIN MIDI port attached to 3.3V Serial using suitable circuitry involving an optocoupler.

Chapter 15: Advanced Techniques

Chapter 16: Other Digital FM Instruments

Howard Massey describes the TX816 like this:

Now this is a synthesizer! In this section, you'll have to forgive my unqualified ravings, because the TX816 is the instrument I'd Most Live To Be Stranded On A Desert Island With.

Guess what, MiniDexed (when running on Raspberry Pi 2 and above) gives you just that, the power of TX816, and more, e.g., effects like reverb.

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