★ HARDWARE Manual ★ SCSP User's Manual
▲ Back ｜ Forward ▼
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 (sawtooth wave), square wave (square wave), triangle wave, and noise (white noise), and you can select any of these.
A block diagram of the LFO is shown in Figure 4.46. Except for the waveform in the case of noise, sawtooth waves, square waves, and triangle waves can be reset and the frequency can be changed. The LFO waveform and modulation level 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 to reset the LFO. Setting this bit to "1B" will reset the LFO. Also, by writing "0B", it will start working.

LFOF [4: 0] (R / W); LFO Frequency
Specifies the oscillation frequency of the LFO.

Table 4.14 Oscillator 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 how much amplitude modulation is applied by the LFO. With this amplitude modulation, the tremolo effect (a phenomenon caused by periodically changing the volume) can be expressed.
 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)
 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)
 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 how much frequency modulation is applied by the LFO. With this frequency modulation, the vibrato effect (a phenomenon caused by periodically fluctuating the oscillation frequency of sound) can be expressed (Table 4.17).
 Table 4.17 Degree of Amplitude Modulation and Frequency Modulation
 ALFOS Mixing to EG PLFOS Impact on pitch
 0 No effect 0 No effect
 1 0.4dB displacement 1 ± 7 cent displacement
 2 0.8dB displacement 2 Displacement of ± 13.5 cents
 3 Displacement of 1.5 dB 3 ± 27 cent displacement
 Four 3dB displacement Four ± 55 cent displacement
 Five 6dB displacement Five Displacement of ± 112 cents
 6 12dB displacement 6 ± 230 cent displacement
 7 24dB displacement 7 Displacement of ± 494 cents
 ▲ Back ｜ Forward ▼
 ★ HARDWARE Manual ★ SCSP User's Manual
 Copyright SEGA ENTERPRISES, LTD., 1997