Basic FM Synthesis on the Yamaha DX7 by Mark Phillips
Introduction This booklet was written to help students to learn the basics of linear FM synthesis and to better understand the Yamaha DX/TX series synthesizers. It is not intended to be a complete course of study on either FM synthesis or the DX7. There are already several very comprehensive books plus a fairly substantial users' manual that provide a mountain of information. The Complete DX7, by Howard Massey, for instance, assumes no prior knowledge or experience in anything related to synthesis.
Basic FM Synthesis -3- 1: FM Demo 1-A (E.G. Control of Timbre) General Description: This voice is designed to imitate the familiar analog synthesis sound of slowly opening and closing a lowpass filter. Since the DX-7 has no filters, this subtractive synthesis sound must be obtained in a completely different method: by linear frequency modulation (FM) using a dynamic index of modulation.
-4- Basic FM Synthesis 2: MW-Demo 1 (Mod Wheel Control of Timbre) General description: This voice is also designed to imitate the familiar analog synthesis sound of opening and closing a low-pass filter. The difference between this voice and the previous one is that the timbral changes are not automatic, but are controlled in real time by the performer using the Modulation Wheel. (Refer to the previous FM-Demo 1A.
Basic FM Synthesis -5- Additional Help for MW-Demo 1: For original DX7: If you are using the Macintosh librarian program, you can select the option "Send Perf. to DX7" under the "Load/Send" menu, then re-select this voice. If you are still unable to get the Mod Wheel to respond, or if you are not using the Macintosh, then you should perform the following steps. When you have completed these, the parameters from your diagram should be in effect on the DX-7 (i.e.
-6- Basic FM Synthesis 3. FM Demo 1-B (E.G. Control of Timbre using Velocity) General Description: This voice, too, is designed to imitate the sound of opening and closing a low-pass filter. The difference between this voice and previous ones is that while the timbral changes are automatic as in FM Demo 1-A, the amount of modulation achieved is dependent on how hard you play on the keyboard. • The harder you hit a key, the more it sounds like FM Demo 1-A.
Basic FM Synthesis -7- 4. FM Demo 1-C (E.G. Control of Timbre, with Rate Scaling) General Description: This is another voice designed to imitate the sound of opening and closing a low-pass filter. In this voice timbral changes again are automatic and the amount of modulation is fixed, as in FM Demo 1-A. The significant difference is that speed of the "opening" and "closing" (i. e. the EG attack and decay of Op. 2) is dependent on how high or low you play on the keyboard.
-8- Basic FM Synthesis 5. FM Demo 1-D (E.G. Control of Timbre) General Description: This voice is also closely related to FM Demo 1-A. The main difference is in the envelope shape of Op. 2, which now has an attack every bit as fast as the carrier (Op. 1). Thus the sound begins with index of modulation at maximum. You no longer hear the "filter opening" aspect of the sound, only the “closing.
Basic FM Synthesis -9- 6. FM Demo 1-E Velocity Control of Carrier (i.e. Amplitude) General Description: This voice is closely related to FM Demo 1-D. The only difference is that now the voice responds to key velocity. The harder (faster) the key is struck, the louder the sound and vice versa. Patch Information: Nearly identical to FM Demo 1-D, except that now the carrier (Op. 1) is set at maximum velocity sensitivity. Exercises: 1. Experiment with various settings of velocity sensitivity for Op. 2 and Op.
-10- Basic FM Synthesis 7. FM Demo 1-F (E.G. Control of Timbre) General Description: This voice is also closely related to FM Demo 1-D. The main difference is in the envelope shape of Op. 2, which now has a perceptibly slower attack. The sound may also be perceived as a sped-up version of FM Demo 1-A. A similar effect would be achieved on an analog synthesizer using an envelope generator (EG) to control a low-pass filter's cut-off frequency.
Basic FM Synthesis -11- 8. FM Demo 1-G (slower carrier E.G. with faster modulator E.G. affects timbre changes, too) General Description: This voice, too, is closely related to FM Demo 1-D. The main difference is in the envelope shape of Op. 1, which now has a perceptibly slower attack. A similar effect might be achieved on an analog synthesizer using an envelope generator (EG) to control the center frequency of a band-pass filter.
-12- Basic FM Synthesis 9. FM Demo 2-A (E.G. Control of Timbre) General Description: While this voice may initially appear to be a duplicate of FM Demo 1-A, when later characteristics of the sound are heard (i.e. when a key is held down for a while, or upon release of the key if it's not held down long), it is clear that there are significant differences. They result primarily from the fact that the envelope for the modulating Op.
Basic FM Synthesis -13- 10. FM Demo 2-B (E.G. Control of Timbre) General Description: This voice is derived from FM Demo 2-A. It has a similar inverted envelope for Op. 2, but the sustain level is kept low. Thus it is indistinguishable from FM Demo 1-D, with its right-side-up envelope, until a key is released. The "metallic" sound of the release is the characteristic sound and one of the primary uses for inverted envelopes. The various DX7 harpsichord presets all use some version of this device.
-14- Basic FM Synthesis 11. Pitch EG Demo 1 General Description: This voice is designed to demonstrate obvious (and dramatic) use of the Pitch EG. The DX-7 has only one envelope for pitch control. It affects all operators simultaneously, whether they be carriers or modulators. There is no way to isolate the effects of the pitch envelope on any given operator, nor is there any way to have more than one pitch envelope per voice. Patch Information: Op. 2 modulates Op.
Basic FM Synthesis -15- 12: Pitch EG Demo 2 General Description: This is another voice with dramatic use of the pitch envelope. A sine wave moves from a very high pitch to normal pitch (“50”) in one smooth descent. Patch Information: Op. 1 is the only operator used so the Pitch EG operates only on it. Note that in order for the Pitch EG to start way above normal, Level 4 needs to be up very high. This is the only way to have the sound begin high suddenly.
-16- Basic FM Synthesis 13: TM Demo (LFO Control of Timbre) General Description: This voice is designed to imitate the subtractive synthesis sound achieved by filter modulation or timbral modulation (TM). The FM equivalent of this sound is arrived at using a low frequency oscillator (LFO) to control the amplitude of the modulating operator. As we have seen before, changes in the amplitude of the modulating operator result in changes in the overall timbre.
Basic FM Synthesis -17- 14: TM Demo-MW (Mod Wheel determines depth of LFO control of timbre) General Description: This voice is also designed to imitate the subtractive synthesis sound achieved by timbral modulation (TM). In this case, the amount of TM can be altered in real time. Specifically, the overall amplitude of Op. 2, as well as the operator's responsiveness to the LFO amplitude modulation, is controlled by the Mod Wheel.
-18- Basic FM Synthesis 15: TM-Organ General Description: This voice is designed to show how the basic concept of timbre modulation can be used as part of a more complex, musically interesting sound. It is included here mainly to show what this discussion of simple FM synthesis might lead to once these concepts are mastered.
Basic FM Synthesis -19- 16: "Wah" Organ General Description: This voice is very similar to the previous TM-Organ. The only difference is that the aspect of timbre control previously accomplished automatically by the LFO is now effected by using the Foot Controller. Play several notes on the keyboard in various registers while moving the foot pedal up and down and listen to the effect on the timbre. Note that the timbre is still touch-sensitive in the same general way as the TMOrgan voice.
-20- Basic FM Synthesis 17: LF Carri 1 General Description: This voice introduces the concept of using an operator as a sine wave LFO by assigning it a very low fixed frequency. Used as a modulator, this low, fixed-frequency operator could provide an alternative type of vibrato control. In this voice, however, the low-frequency operator functions as a carrier, causing cyclic changes in timbre. Patch Information: Op. 1 is set to a frequency of 1Hz, the lowest possible fixed-frequency on the DX7.
Basic FM Synthesis -21-
-22- Basic FM Synthesis 19: LF Carri 3 General Description: This voice is designed to expand still further on the basic concept of low- frequency carriers. In this voice another pair of operators with an LF carrier is added. Patch Information: The settings for Op. 1, Op. 2, Op. 3, and Op. 4 are identical to LF Carri 2. Now, Op. 5 and Op. 6 are included, with settings that nearly duplicate those of the other pairs. The fixed-frequency value for the LF Op. 5 is the only difference. In order for Op.
Basic FM Synthesis -23- 20: Addsynth 1 General Description: This voice is constructed using additive synthesis. With only six sine waves to sum, the DX7 is not a powerful tool for this method of sound construction. But it does provide the basics for using it alone or in combination with FM synthesis. Algorithm 32, with all six operators functioning as carriers, allows maximum additive synthesis power and flexibility. Patch Information: In Algorithm 32, all six operators are used as carriers.
-24- Basic FM Synthesis 21: Addsynth 2 General Description: This voice is similar to the previous Addsynth 1. In fact, the steady-state sound of a note that has been held down 3 or 4 seconds is absolutely identical. The only differences occur at the beginning of the sound. The envelope generators are designed so as to bring in each harmonic of the sound separately. Patch Information: Identical to Addsynth 1 except for EG settings. Ops.
Basic FM Synthesis -25- 22: Addsynth 3 General Description: This voice is similar to the previous Addsynth 2, but this time the entrances of the various harmonics have a stronger, more bell-like attack and are higher pitched than before. The sound also dies away more slowly. Patch Information: EG settings similar to Addsynth 2 (Ops. 2-6: Level 1 is ca. 50, Rate 1 ranges from 6 to 23), but now Rate 2 is above 90 (bell-like attack) and all operators have a Rate 4 of 30 (slow decay).
-26- Basic FM Synthesis 23: Addsynth 4 General Description: This voice is derived from Addsynth 1 and shares an identical steady-state sound with it. The only difference is that the harmonics smoothly, but quickly fade in one by one over a short span of time (ca. 1 sec.). Notice that this effect is very similar to the sound of a low-pass filter controlled by an EG, which in turn we've seen to be similar in effect to the linear FM sounds introduced at the begining of this book. (i.e.
Basic FM Synthesis -27- 24: Addsynth 5 General Description: This voice, too, is derived from Addsynth 1 and shares an identical steady-state sound with it. It also shares with Addsynth 4 the concept of harmonics fading in one by one over a period of time. The differences this time are that the harmonics enter in opposite order, from high to low, and take longer to enter. This is of course similar to opening up a high-pass filter.
-28- Basic FM Synthesis Expressive Pitch Bend with Timbre Variation On many acoustic instruments, expressive pitch bending also results in changes timbre (or tone color). Often (as in a saxophone or harmonica, for example) it is a matter of losing some of the original brilliance or edginess of the sound as the pitch is bent downward.
Basic FM Synthesis -29- Now you can use your index and middle fingers together to control pitch bend and timbre simultaneously by moving the two wheels together. Using pitch bends in the minus range with parallel movements of the Mod Wheel will vary the patch's timbre between its original sound and one several shades darker in direct correlation to the amount of pitch bend.
-30- Basic FM Synthesis Addendum/Update for Basic FM Synthesis booklet Though the demos in this booklet were written for the original DX7, the concepts behind these demo sounds are applicable to any Yamaha FM synthesizer. All of the actual patches in the booklet are completely compatible with any 6-operator FM synthesizer such as the TX7, DX7II,TX802, SY77 (which are all available in both studios at O.U.).
