<19/29>SCSP User's Manual/4.2.5PITCH

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SCSP User's Manual/4.2 Sound source register

■PITCH register

OCT[3:0](R/W) ; OCTave

"OCT" is a register that has the function of raising or lowering the sound frequency by an octave for the waveform data stored in memory.

FNS[9:0](R/W); Frequency Number Switch

This register has a more detailed sounding frequency setting function between the upper and lower octaves of "OCT". If the "FNS" value and "OCT" value are both "0H", the pitch will match the sampling source. Figure 4.45 shows the relationship between the "FNS" and "OCT" values.

Figure 4.45 Relationship between OCT and FNS

The actual pitch (n) is calculated using the formula shown below.

The value obtained by this formula is expressed in cents.

Let me explain about cents here.

1 cent is 2 ^1/1200 = 1.000577789 times. Also, one octave is 1200 cents. When it is n cents, it is 2 to the original frequency. times {=(1.000577789) ⁿ }. Therefore, the frequency Fn[Hz] of a sound that is n cents higher than the basic frequency Fo[Hz] can be calculated using the following formula.

The actual frequency for the number of cents at this time is shown in Table 4.12.

Table 4.12 Actual frequency versus number of cents

number of cents	Real frequency wave number value (×Fo)
0	1.000000000
100	1.059463094
200	1.122462048
300	1.189207115
400	1.259921050
500	1.334839854
600	1.414213562
700	1.498307077
800	1.587401052
900	1.681792830
1000	1.781797436
1100	1.887748625
1200	2.000000000

Next, we will explain how to set "FNS" and "OCT" using an example where the C4 (C) sound is sampled at 44.1KHz.
The "FNS" value when P[Cent] can be calculated using the following formula.

From this formula, it is possible to output at any frequency by setting each parameter as shown in Table 4.13.

Table 4.13 FNS.OCT parameter table

pitch name	NOTE number	PITCH[Cent]	FNS[9:0][DEC]	FNS[9:0][HEX]	OCT[3:0][HEX]
B3	59	1100	909.1	38D	F
C4	60	0	0.0	0	0
C4#	61	100	60.9	03D	0
D4	61	200	125.4	07D	0
D4#	63	300	193.7	0C2	0
E4	64	400	266.2	10A	0
F4	65	500	342.9	157	0
F4#	66	600	424.2	1A8	0
G4	67	700	510.3	1FE	0
G4#	68	800	601.5	25A	0
A4	69	900	698.2	2BA	0
A4#	70	1000	800.6	321	0
B4	71	1100	909.1	38D	0
C5	72	0	0.0	0	1

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