We've just updated MediaWiki and its underlying software. If anything doesn't look or work quite right, please mention it to us. --RanAS
S-DSP/Noise: Difference between revisions
From SnesLab
(see also Bit-Of-Confusion) |
m (hyphen in linear-feedback) |
||
| Line 3: | Line 3: | ||
Noise clock table | Noise clock table | ||
Hardware noise on the SNES is generated by a 15-bit Fibonacci [https://www.eetimes.com/tutorial-linear-feedback-shift-registers-lfsrs-part-1/ linear feedback shift register]. [1] Unlike the NES which has two hardware noise timbres, the SNES only has one. The taps are located at bits 0 & 1, which are XOR'd together and fed back into bit 14 while the whole register shifts to the right (dividing everything else by two). [2] Its initial seed value is 4000h. | Hardware noise on the SNES is generated by a 15-bit Fibonacci [https://www.eetimes.com/tutorial-linear-feedback-shift-registers-lfsrs-part-1/ linear-feedback shift register]. [1] Unlike the NES which has two hardware noise timbres, the SNES only has one. The taps are located at bits 0 & 1, which are XOR'd together and fed back into bit 14 while the whole register shifts to the right (dividing everything else by two). [2] Its initial seed value is 4000h. | ||
Note that the noise sampling frequency is the perceived pitch (due to overtones) even though it is double ([https://www.techtarget.com/whatis/definition/Nyquist-Theorem Nyquist]) that of the fundamental. The [[S-DSP/Gaussian Filter|Gaussian interpolator]] does not operate on the hardware noise generator. | Note that the noise sampling frequency is the perceived pitch (due to overtones) even though it is double ([https://www.techtarget.com/whatis/definition/Nyquist-Theorem Nyquist]) that of the fundamental. The [[S-DSP/Gaussian Filter|Gaussian interpolator]] does not operate on the hardware noise generator. | ||
Revision as of 09:00, 11 July 2023
Noise clock table
Hardware noise on the SNES is generated by a 15-bit Fibonacci linear-feedback shift register. [1] Unlike the NES which has two hardware noise timbres, the SNES only has one. The taps are located at bits 0 & 1, which are XOR'd together and fed back into bit 14 while the whole register shifts to the right (dividing everything else by two). [2] Its initial seed value is 4000h.
Note that the noise sampling frequency is the perceived pitch (due to overtones) even though it is double (Nyquist) that of the fundamental. The Gaussian interpolator does not operate on the hardware noise generator.
| Value | Sampling Frequency | Pitch | Example |
|---|---|---|---|
| 00 | 0 Hz | off | |
| 01 | 16 Hz | C0 - 38¢ | |
| 02 | 21 Hz | E0 + 33¢ | |
| 03 | 25 Hz | G0 + 35¢ | |
| 04 | 31 Hz | B0 + 7¢ | |
| 05 | 42 Hz | E1 + 33¢ | |
| 06 | 50 Hz | G1 + 35¢ | |
| 07 | 63 Hz | B1 + 35¢ | |
| 08 | 83 Hz | E2 + 12¢ | |
| 09 | 100 Hz | G2 + 35¢ | |
| 0A | 125 Hz | B2 + 21¢ | |
| 0B | 167 Hz | E3 + 23¢ | |
| 0C | 200 Hz | G3 + 35¢ | |
| 0D | 250 Hz | B3 + 21¢ | |
| 0E | 333 Hz | E4 + 18¢ | |
| 0F | 400 Hz | G4 + 35¢ | |
| 10 | 500 Hz | B4 + 21¢ | |
| 11 | 667 Hz | E5 + 20¢ | |
| 12 | 800 Hz | G5 + 35¢ | |
| 13 | 1.0 kHz | B5 + 21¢ | |
| 14 | 1.3 kHz | E6 - 24¢ | |
| 15 | 1.6 kHz | G6 + 35¢ | |
| 16 | 2.0 kHz | B6 + 21¢ | |
| 17 | 2.7 kHz | E7 + 41¢ | |
| 18 | 3.2 kHz | G7 + 35¢ | |
| 19 | 4.0 kHz | B7 + 21¢ | |
| 1A | 5.3 kHz | E8 + 9¢ | |
| 1B | 6.4 kHz | G8 + 35¢ | |
| 1C | 8.0 kHz | B8 + 21¢ | |
| 1D | 10.7 kHz | E9 + 25¢ | |
| 1E | 16 kHz | B9 + 21¢ | |
| 1F | 32 kHz | B10 + 21¢ |
See Also
References
- page 3-7-8 of the official Super Nintendo development manual
- [1] https://github.com/ares-emulator/ares/blob/master/ares/sfc/dsp/dsp.hpp#L76
- [2] https://github.com/ares-emulator/ares/blob/master/ares/sfc/dsp/misc.cpp#L26