2. THE SYNTHESIS OF SOUNDS ^

2 - 3 The Basic Process Of Sound Synthesis

Waveforms:
The waveforms talked about here are the unfiltered simple waveforms that form the basis of sound synthesis.

(Triangle):

By using a filter this waveform may bc turned into a sinewave. This waveform may be thought of as being the most basic or standard. It has a soft rounded tone color which makes it appropriate for such sounds as a flute, piccolo, or organ.

(Sawtooth):

Since there is a certain amount of upper harmonic elements in this waveform, it is easy to use filtering to produce a wide variation in sound quality.

(Rectangle 1:1):

Since this waveform does not contain even harmonic elements, the sound quality is on the heavy, dull side.

(Rectangle 1:2) :

Since the third harmonic element is missing, the tone color of this waveform has more upper harmonic components than the 1:1 REC waveform.

(Pulse 1:9):

Since this waveform is very rich in upper harmonic components, the tone color is very bright and sparkling.

(Pulse Width Modulation 3:7, 7:3) :

MG2 (and other inputs) may be used to modulate the pulse width of this waveform. Pulse width may be varied by VP2 to obtain a variety of effects such as two instruments playing in unison.

ENVELOPE:

In contrast to the waveform itself, an envelope is the contour that may be given to the waveform by using an envelope generator to control attack time, sustain level, and decay time. These have to do with the volume of a sound and the changes in volume over time. Figure 34 shows the envelope generating parameters of the PS-3100. Following this are some examples of the envelopes of some typical instruments.

NOTE: These examples should be thought of as standards from which the envelope may vary depending on the settings of other controls such as fc and EXPAND.

Figure 34 - the Envelope Generating parameters of the PS-3100

Figure 35 - the Envelope Generating parameters of an organ

Figure 36 - the Envelope Generating parameters of a brass instrument

Figure 37 - the Envelope Generating parameters of a stringed instrument

Figure 38 - the Envelope Generating parameters of a plucked or percussive instrument

The effect of the EXPAND function:

The EXPAND function has the effect of varying the fc depending on the setting of the EM section envelope generator. It is useful for creating sound effects or woodwind type sounds where the tone color varies along with the volume.

When using the EXPAND effect, the fc may vary more or less suddenly depending on the PEAK setting. If the Peak setting is very high, the result will be an unreal sound inappropriate for the synthesis of ordinary musical instruments.

Figure 39 - The Waveform of a Woodwind Instrument

In the case of synthesizing a piano or other sound having a similar decay period, the EXPAND control can be used to give the sound a sharp attack time and appropriate decay time in terms of both volume and tone color. However, if the PEAK setting is too high, the decay time will be heard as being shorter than the actual DECAY setting would make one expect. Therefore, the DECAY setting should be made after you have set the EXPAND and PEAK controls.

Figure 40 - The Waveform of an Electric Piano

Figure 41 - Vibrato setting chart

The VIBRATO effect (one of the more frequently used effects):

Needless to say, the MG-1 is used to modulate the oscillator frequency of the SG (VCO) but it must be remembered that in the case of real musical instruments and the human voice there are changes in both tone color and volume simultaneous with changes in pitch. This effect may be simply duplicated by using filter modulation and amplitude modulation. Besides these methods one may get another type of interesting result by using the RESONATORS (employ MODULATION GENERATOR 2) for a vibrato effect.

Note: The triangle waveform is the most appropriate to use for most vibrato effects.

Figure 42 - BEND setting chart

The BEND effect (another often used effect):

This effect consists of a change in pitch that takes place over a set length of time after a key is pressed. (The pitch may return to its original level or change completely.) If this effect is applied quickly over a short period of time, the result will be similar to a woodwind or human voice. On the other hand, a polyphonic glide effect may be obtained by drawing out the effect by increasing the delay time.

Based on the above materials let's try putting together a single complex sound.

(Ex.) BRASS
(WAVEFORM).................SAW
(SCALE)..........................16'-4'
(ENVELOPE)...................ATTACK 0 - 5; DECAY 0 - 5; SUSTAIN 5 -10; HALF DAMP: ON



(EXPAND, PEAK)..........Set to the levels you like.
(VIBRATO).....................Set the speed and amount of modulation as you like.

(Ex.) STRINGS

(WAVEFORM) SAW
(SCALE) 16' - 4'
(ENVELOPE) ATTACK 3 - 6; DECAY 0; SUSTAIN 5-10; HALF DAMP: ON

(PEAK) (less than 5)
(EXPAND) 0
(VIBRATO) Set the speed and modulation as you like. The ENSEMBLE switch may also be turned on.

2-1 Thinking About Sound Synthesis
2 - 2 Creating Sounds Using The Built-In Patch
2 - 3 The Basic Process Of Sound Synthesis
2 - 4 Understanding The Patch And Its Use