<20/29>SCSP User's Manual/4.2.6LFO

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SCSP User's Manual/4.2 Sound source register

■LFO register

An LFO is a low frequency oscillator used to modulate audio signals.
One LFO is installed in each slot, and each slot has an output for amplitude modulation and an output for frequency modulation.
There are four types of LFO output waveforms: sawtooth wave, square wave, triangle wave, and noise (white noise), and you can choose any of these.
The block diagram of the LFO is shown in Figure 4.46. Sawtooth waves, square waves, and triangle waves, except for noise waveforms, can be reset and their frequencies can be changed. Additionally, the LFO waveform and modulation depth can be set independently for the amplitude modulation side and frequency modulation side.

Figure 4.46 LFO block diagram

LFORE(R/W) ; LFO REset

Specifies whether or not to reset the LFO. Setting this bit to "1B" resets the LFO. Also, by writing "0B", it starts operating.

LFOF[4:0](R/W); LFO Frequency

Specifies the oscillation frequency of the LFO.

Table 4.14 Oscillator oscillation frequency

LFOF	Oscillation frequency (Hz)	LFOF	Oscillation frequency (Hz)
00H	0.17	10H	2.87
01H	0.19	11H	3.31
02H	0.23	12H	3.92
03H	0.27	13H	4.79
04H	0.34	14H	6.15
05H	0.39	15H	7.18
06H	0.45	16H	8.6
07H	0.55	17H	10.8
08H	0.68	18H	14.4
09H	0.78	19H	17.2
0AH	0.92	1AH	21.5
0BH	1.10	1BH	28.7
0CH	1.39	1CH	43.1
0DH	1.60	1DH	57.4
0EH	1.87	1EH	86.1
0FH	2.27	1FH	172.3

ALFOS[2:0](R/W) ; Amplitude-LFO Sensitivity

Specifies the amount of amplitude modulation applied by the LFO. This amplitude modulation allows you to express a tremolo effect (a phenomenon caused by periodically varying the volume).

ALFOWS[1:0](R/W) ; Amplitude-LFO Wave Select

Specify the AM modulation waveform as shown in Table 4.15.

Table 4.15 AM modulation waveform by LFO

ALFOWS	AM modulation (ALFO)
ALFOWS	Volume	ALFO[7:0]	LFO waveform
0	-0dB	0 : FF
1	-0dB	0 : FF
2	-0dB	0 : FF
3	-0dB	0 : FF

PLFOWS[1:0](R/W); Pitch-LFO Wave Select

Specify the PM modulation waveform as shown in Table 4.16.

Table 4.16 PM modulation waveform by LFO

ALFOWS	PM modulation (ALFO)
ALFOWS	pitch	PLFO[7:0]	LFO waveform
0	+ 0 -	7F 00 80
1	+ 0 -	7F 00 80
2	+ 0 -	7F 00 80
3	+ 0 -	7F 00 80

ALFO [7:0] and PLFO [7:0] represent the bit width (data) output by the LFO.

PLFOS[2:0](R/W); Pitch-LFO Sensitivity

Specifies the amount of frequency modulation applied by the LFO. This frequency modulation makes it possible to express the vibrato effect (a phenomenon caused by periodically varying the oscillation frequency of a sound) (Table 4.17).

Table 4.17 Degree of amplitude modulation and frequency modulation

ALFOS	Mixing to EG	PLFOS	Effect on pitch
0	No effect	0	No effect
1	0.4dB displacement	1	±7 cents displacement
2	0.8dB displacement	2	±13.5 cents displacement
3	1.5dB displacement	3	±27 cents displacement
4	3dB displacement	4	±55 cents displacement
5	6dB displacement	5	±112 cents displacement
6	12dB displacement	6	±230 cents displacement
7	24dB displacement	7	±494 cents displacement

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