<17/29>SCSP User's Manual/How to use the FM sound source method/3

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SCSP User's Manual/4.3 Sound source register

Until now, we have calculated "MDXSL" and "MDYSL", but from the slot numbers of the modulator side (modulator) and the modulated side (carrier), we can use the parameter correspondence table in Table 4.16 to find "MDXSL" " and "MDYSL" values can be derived.
Using the parameter table below, find "MDXSL" and "MDYSL" in Figure 4.33.

(1) Parameters set in slot 0

Slot 0 has a self-feedback configuration, so the carrier slot number and modulator slot number are "00". At this time, "MDXSL" and "MDYSL" are from the parameter table,

Latest sample. ．． ．． ．． ．． 20H
Past samples. ．． ．． ．． 00H

It becomes. As mentioned earlier, in the case of self-feedback, if the same generation is used as input, there is a possibility of oscillation, so avoid using this method.

(2) Parameters set for slot 2

Slot 2 has a multiple input configuration.
First, when slot 1 is input, the carrier slot number is "02" and the modulator slot number is "01". At this time, "MDXSL" and "MDYSL" are from the parameter table,

Latest sample. ．． ．． ．． ．． 1FH
Past samples. ．． ．． ．． 3FH

It becomes.

Next, when inputting slot 0, the carrier slot number will be "02" and the modulator slot number will be "00". At this time, "MDXSL" and "MDYSL" are from the parameter table,

Latest sample. ．． ．． ．． ．． 1EH
Past samples. ．． ．． ．． 3EH

It becomes.

(3) Parameters set in slot 3

Slot 3 takes the output of slot 2 as its input. Therefore, the carrier slot number will be "03" and the modulator slot number will be "02". At this time, "MDXSL" and "MDYSL" are from the parameter table,

Latest sample. ．． ．． ．． ．． 1FH
Past samples. ．． ．． ．． 3FH

It becomes.

Table 4.16 Relationship between MDXSL/MDYSL and slots

MDXSL/MDYSL carrier slot number Parameter 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 value (SAMPLE) Latest Past Modulation slot number SLOT 00~31 20H 00H 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 21H 01H 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 22H 02H 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 23H 03H 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 24H 04H 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 25H 05H 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 26H 06H 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 27H 07H 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 28H 08H 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 29H 09H 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 2AH 0AH 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 2BH 0BH 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 2CH 0CH 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 2CH 0DH 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 2EH 0EH 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 2FH 0FH 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 30H 10H 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 31H 11H 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 00 32H 12H 18 19 20 21 22 23 24 25 26 27 28 29 30 31 00 01 33H 13H 19 20 21 22 23 24 25 26 27 28 29 30 31 00 01 02 34H 14H 20 21 22 23 24 25 26 27 28 29 30 31 00 01 02 03 35H 15H 21 22 23 24 25 26 27 28 29 30 31 00 01 02 03 04 36H 16H 22 23 24 25 26 27 28 29 30 31 00 01 02 03 04 05 37H 17H 23 24 25 26 27 28 29 30 31 00 01 02 03 04 05 06 38H 18H 24 25 26 27 28 29 30 31 00 01 02 03 04 05 06 07 39H 19H 25 26 27 28 29 30 31 00 01 02 03 04 05 06 07 08 3AH 1AH 26 27 28 29 30 31 00 01 02 03 04 05 06 07 08 09 3BH 1BH 27 28 29 30 31 00 01 02 03 04 05 06 07 08 09 10 1CH 3CH 28 29 30 31 00 01 02 03 04 05 06 07 08 09 10 11 1DH 3DH 29 30 31 00 01 02 03 04 05 06 07 08 09 10 11 12 1EH 3EH 30 31 00 01 02 03 04 05 06 07 08 09 10 11 12 13 1FH 3FH 31 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 MDXSL/MDYSL carrier slot number Parameter 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 value (SAMPLE) Latest Past Modulation slot number SLOT 00~31 20H 00H 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 21H 01H 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 00 22H 02H 18 19 20 21 22 23 24 25 26 27 28 29 30 31 00 01 23H 03H 19 20 21 22 23 24 25 26 27 28 29 30 31 00 01 02 24H 04H 20 21 22 23 24 25 26 27 28 29 30 31 00 01 02 03 25H 05H 21 22 23 24 25 26 27 28 29 30 31 00 01 02 03 04 26H 06H 22 23 24 25 26 27 28 29 30 31 00 01 02 03 04 05 27H 07H 23 24 25 26 27 28 29 30 31 00 01 02 03 04 05 06 28H 08H 24 25 26 27 28 29 30 31 00 01 02 03 04 05 06 07 29H 09H 25 26 27 28 29 30 31 00 01 02 03 04 05 06 07 08 2AH 0AH 26 27 28 29 30 31 00 01 02 03 04 05 06 07 08 09 2BH 0BH 27 28 29 30 31 00 01 02 03 04 05 06 07 08 09 10 2CH 0CH 28 29 30 31 00 01 02 03 04 05 06 07 08 09 10 11 2DH 0DH 29 30 31 00 01 02 03 04 05 06 07 08 09 10 11 12 2EH 0EH 30 31 00 01 02 03 04 05 06 07 08 09 10 11 12 13 2FH 0FH 31 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 30H 10H 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 31H 11H 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 32H 12H 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 33H 13H 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 34H 14H 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 35H 15H 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 36H 16H 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 37H 17H 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 38H 18H 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 39H 19H 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 3AH 1AH 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 3BH 1BH 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 1CH 3CH 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 1DH 3DH 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 1EH 3EH 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 1FH 3FH 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

*How to read the table

First find the slot number on the carrier side, then find the slot number of the modulator that will be entered into it. Find the corresponding number of samples in the horizontal column.

Next, we will explain "MDL" (Modulation Level).
"MDL" is a parameter that sets the modulation depth (degree of modulation) by the modulation signal applied to modulation inputs X and Y. Increasing this value will deepen the frequency modulation, and decreasing this value will make the frequency modulation shallower (Figure 4.32).

Figure 4.32 MDL modulation depth

This section explains the modulation degree based on the "MDL" setting value. Table 4.15 shows that the modulation depth is ±nπ depending on the "MDL" setting value.
Each sound slot data input to modulation inputs X and Y is averaged by the averaging calculation section. If the data input to X is XD, the data input to Y is YD, and the output of the averaging operation section is ZD, it can be expressed as the following formula.


ZD = (XD + YD) ÷ 2

This ZD undergoes level adjustment by "MDL" and is sent to the slot address pointer (phase adder).

Figure 4.33 Maximum displacement by waveform read address

In FM voice synthesis, if no modulation waveform is added, the time-phase function is linear. However, when a modulated waveform is added, the displacement corresponding to the modulated waveform is added, so the linear time-phase waveform becomes nonlinear. This displacement is maximum when ZD takes the ±maximum value. The modulation degree of MDL represents the displacement (maximum displacement) of the waveform address when ZD takes the ±maximum value, with one cycle of waveform data (sine wave) = 1K words.

Table 4.10 Maximum address displacement by register setting value

MDL[3:0]	0-4	5	6	7	8	9	A	B	C	D	E	F
Maximum address displacement ±	0	32	64	128	256	512	1024	2048	4096	8192	16384	32768

Comparing Table 4.16 and Table 4.10, we obtain the relationship π = 512 (when MDL = AH). In Table 4.16, one cycle of waveform data (sine wave) is considered to be 1K words (1024 words), but mathematically, the length of one cycle of the waveform is defined as 2π. Therefore, in this FM voice synthesis, we are using a sine wave with 1 cycle = 1K words, so the maximum address displacement of 512 can be expressed as π. The expression method using π is valid only when one period of waveform data is 1K words. In other cases, use the expression method using address displacement in Table 4.10.

When performing FM voice synthesis, please have three cycles of waveform data. The reason is that address displacement occurs. With SCSP hardware, it is necessary to store waveform data in memory up to 1K word address displacement (MDL="AH"), but the hardware automatically performs clipping processing for data exceeding 1K words. Therefore, there is no need to store more than 1K words of extra waveform data.

Figure 4.34 Address displacement during FM synthesis

When performing FM voice synthesis, place extra data for the address displacement. Basically, if it is ±π, there will be no operational problem by setting the waveform data for π before "SA" and after "LEA" (if PLFO is not used). However, it is better to set data for three cycles as shown in Figure 4.34.

*About clipping processing

This is related to the address displacement described earlier. The range of address displacement varies by a maximum of ±32768 addresses depending on "MDL", so 32 cycles (32K words) of waveform data are required before and after one cycle (1K words) of the basic waveform, for a total of 65K words. Requires a large amount of memory.
Therefore, in SCSP, if the displacement exceeds 1K words, clipping (processing to prevent it from exceeding) is performed and the displacement is returned to 0. As a result, no matter how much displacement there is, a total of 3K words of waveform data is enough to handle it.
Also, since the effective address bits prepared for displacement are 10 bits, we decided to perform clipping processing.

Figure 4.35 Wave data during clipping processing

As shown in Figure 4.35, even if it exceeds the preliminary waveform after displacement, it returns to 0 when the phase exceeds 2π.

Next, I will explain how to assemble the FM configuration (algorithm) in SCSP. SCSP slots basically have a structure of 2 inputs and 1 output, so the maximum number of slots that can be connected (and modulated) to one slot is 2. .

Figure 4.36 Number of slot connections

As shown in Figure 4.36, modulation is possible with up to two. Also, considering that modulation data (source) is brought from the sound stack, SCSP allows FM configurations such as those shown in Figure 4.37, Figure 4.38, Figure 4.39, and Figure 4.40 to be constructed.
(Figure 4.37 shows a configuration in which a slot subjected to self-feedback is modulated using other slots, Figure 4.38 shows multistage feedback including multiple slots, Figure 4.39 shows a composite feedback system that combines multistage feedback and self-feedback, and Figure 4.40 represents a composite modulation type in which each slot is modulated with a different slot with multi-stage feedback.)

Figure 4.37 Self-feedback modulation

Figure 4.38 Multi-stage feedback

Figure 4.39 Composite feedback

Figure 4.40 Complex modulation

Figures 4.41 and 4.42 show specific examples of basic FM configurations. Please use this as a reference when performing FM voice synthesis. The upper two lines of each slot represent the modulation input, and the lower line represents the slot output.
Also, in Figures 4.41 and 4.42, it appears that only one connection is made between the slots, so in reality, make sure to also connect the part shown by the broken line.

Figure 4.41 FM configuration algorithm pattern 1

Figure 4.42 FM configuration algorithm pattern 2

In FM speech synthesis, the top slot has nothing connected to it unless there is self-feedback. In this case, set "MDL" to a value between 0B" and "4B" and set the modulation depth to "0". This allows you to set the modulation input to "0". .

*Definition of top slot

Top slot refers to the top slot of each tower in the algorithm. In Figure 4.43, there are three towers: S0, S1, S2, and S3, S4, S5, and S6. These top slots are S0, S1, and S6.

Figure 4.43 7-slot FM configuration

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