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# Super Nintendo Entertainment System (SNES) / Super Famicom
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the successor to NES to compete with Genesis, packing superior graphics and sample-based audio.
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its Sony-developed audio system features a DSP chip, SPC700 CPU, and 64KB of dedicated SRAM used by both.
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this whole system itself is pretty much a separate computer that the main CPU needs to upload its program and samples to.
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Furnace communicates with the DSP directly and provides a full 64KB of memory. this memory might be reduced excessively on ROM export to make up for playback engine and pattern data. you can go to window > statistics to see how much memory your samples are using.
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some notable features of the DSP are:
- pitch modulation, meaning that you can use 2 channels to make a basic FM synth without eating up too much memory.
- a built in noise generator, useful for hi-hats, cymbals, rides, effects, among other things.
- per-channel echo, which unfortunately eats up a lot of memory but can be used to save channels in songs.
- an 8-tap FIR filter for the echo, which is basically a procedural low-pass filter that you can edit however you want.
- sample loop, but the loop points have to be multiples of 16.
- left/right channel invert for surround sound.
- ADSR and gain envelope modes.
- 7-bit volume per channel.
- sample interpolation, which is basically a low-pass filter that gets affected by the pitch of the channel.
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Furnace also allows the SNES to use wavetables (and the wavetable synthesizer) in order to create more 'animated' sounds, using less memory than regular samples. this however is not a hardware feature, and might be difficult to implement on real hardware.
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# effects
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- `10xx` : **set waveform.**
- `11xx` : **toggle noise mode.**
- `12xx` : **toggle echo on this channel.**
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- `13xx` : **toggle pitch modulation.** frequency modulation by the previous channel's output. no effect on channel 1.
- `14xy` : **toggle inverting the left or right channels.** `x` is left, `y` is right.
- `15xx` : **set envelope mode.** see gain chart below for `1` through `5` .
- `0` : ADSR mode.
- `1` : gain (direct). volume holds at one level.
- `2` : linear decrement. volume lowers by subtractions of 1/64.
- `3` : exponential decrement. volume lowers by multiplications of 255/256.
- `4` : linear increment. volume rises by additions of 1/64.
- `5` : bent line (inverse log) increment. volume rises by additions of 1/64 until 3/4, then additions of 1/256.
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- `16xx` : **set gain.** `00` to `7F` if direct, `00` to `1F` otherwise.
- `18xx` : **enable echo buffer.**
- `19xx` : **set echo delay.** range is `0` to `F` .
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- `1Axx` : **set left echo channel volume.** \
`1Bxx` : **set right echo channel volume.** \
`1Cxx` : **set echo feedback.**
- all of these are signed numbers.
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- `00` to `7F` for 0 to 127.
- `80` to `FF` for -128 to -1.
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- setting these to -128 is not recommended as it may cause echo output to overflow and therefore click.
- `1Dxx` : **set noise generator frequency.** range is `00` to `1F` . see noise frequencies chart below.
- `1Exx` : **set left dry / global volume.** \
`1Fxx` : **set right dry / global volume.**
- these do not affect echo.
- `20xx` : **set attack.** range is `0` to `F` .\
`21xx` : **set decay.** range is `0` to `7` .\
`22xx` : **set sustain.** range is `0` to `7` .\
`23xx` : **set release.** range is `00` to `1F` .
- these four are only used in ADSR envelope mode. see ADSR chart below.
- `30xx` : **set echo filter coefficient 0.** \
`31xx` : **set echo filter coefficient 1.** \
`32xx` : **set echo filter coefficient 2.** \
`33xx` : **set echo filter coefficient 3.** \
`34xx` : **set echo filter coefficient 4.** \
`35xx` : **set echo filter coefficient 5.** \
`36xx` : **set echo filter coefficient 6.** \
`37xx` : **set echo filter coefficient 7.**
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- all of these are signed numbers.
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- `00` to `7F` for 0 to 127.
- `80` to `FF` for -128 to -1.
- _Note:_ Be sure the sum of all coefficients is between -128 and 127. sums outside that may result in overflow and therefore clicking.
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- see [SnesLab ](https://sneslab.net/wiki/FIR_Filter ) for a full explanation and examples.
# tables
## ADSR
| attack | 0→1 time | decay | 1→S time | sustain | ratio | release | S→0 time
| -----: | -------: | ----: | -------: | ------: | :---: | ------: | -------:
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| `00` | 4.1s | `00` | 1.2s | `00` | 1/8 | `00` | ∞
| `01` | 2.5s | `01` | 740ms | `01` | 2/8 | `01` | 38s
| `02` | 1.5s | `02` | 440ms | `02` | 3/8 | `02` | 28s
| `03` | 1.0s | `03` | 290ms | `03` | 4/8 | `03` | 24s
| `04` | 640ms | `04` | 180ms | `04` | 5/8 | `04` | 19s
| `05` | 380ms | `05` | 110ms | `05` | 6/8 | `05` | 14s
| `06` | 260ms | `06` | 74ms | `06` | 7/8 | `06` | 12s
| `07` | 160ms | `07` | 37ms | `07` | 1 | `07` | 9.4s
| `08` | 96ms | | | | | `08` | 7.1s
| `09` | 64ms | | | | | `09` | 5.9s
| `0A` | 40ms | | | | | `0A` | 4.7s
| `0B` | 24ms | | | | | `0B` | 3.5s
| `0C` | 16ms | | | | | `0C` | 2.9s
| `0D` | 10ms | | | | | `0D` | 2.4s
| `0E` | 6ms | | | | | `0E` | 1.8s
| `0F` | 0ms | | | | | `0F` | 1.5s
| | | | | | | `10` | 1.2s
| | | | | | | `11` | 880ms
| | | | | | | `12` | 740ms
| | | | | | | `13` | 590ms
| | | | | | | `14` | 440ms
| | | | | | | `15` | 370ms
| | | | | | | `16` | 290ms
| | | | | | | `17` | 220ms
| | | | | | | `18` | 180ms
| | | | | | | `19` | 150ms
| | | | | | | `1A` | 110ms
| | | | | | | `1B` | 92ms
| | | | | | | `1C` | 74ms
| | | | | | | `1D` | 55ms
| | | | | | | `1E` | 37ms
| | | | | | | `1F` | 18ms
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reference: [Super Famicom Development Wiki ](https://wiki.superfamicom.org/spc700-reference#dsp-voice-register:-adsr-1097 )
## gain
value | linear inc. | bent line inc. | linear dec. | exponent dec.
----: | ----------: | -------------: | ----------: | ------------:
`00` | ∞ | ∞ | ∞ | ∞
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`01` | 4.1s | 7.2s | 4.1s | 38s
`02` | 3.1s | 5.4s | 3.1s | 28s
`03` | 2.6s | 4.6s | 2.6s | 24s
`04` | 2.0s | 3.5s | 2.0s | 19s
`05` | 1.5s | 2.6s | 1.5s | 14s
`06` | 1.3s | 2.3s | 1.3s | 12s
`07` | 1.0s | 1.8s | 1.0s | 9.4s
`08` | 770ms | 1.3s | 770ms | 7.1s
`09` | 640ms | 1.1s | 640ms | 5.9s
`0A` | 510ms | 900ms | 510ms | 4.7s
`0B` | 380ms | 670ms | 380ms | 3.5s
`0C` | 320ms | 560ms | 320ms | 2.9s
`0D` | 260ms | 450ms | 260ms | 2.4s
`0E` | 190ms | 340ms | 190ms | 1.8s
`0F` | 160ms | 280ms | 160ms | 1.5s
`10` | 130ms | 220ms | 130ms | 1.2s
`11` | 96ms | 170ms | 96ms | 880ms
`12` | 80ms | 140ms | 80ms | 740ms
`13` | 64ms | 110ms | 64ms | 590ms
`14` | 48ms | 84ms | 48ms | 440ms
`15` | 40ms | 70ms | 40ms | 370ms
`16` | 32ms | 56ms | 32ms | 290ms
`17` | 24ms | 42ms | 24ms | 220ms
`18` | 20ms | 35ms | 20ms | 180ms
`19` | 16ms | 28ms | 16ms | 150ms
`1A` | 12ms | 21ms | 12ms | 110ms
`1B` | 10ms | 18ms | 10ms | 92ms
`1C` | 8ms | 14ms | 8ms | 74ms
`1D` | 6ms | 11ms | 6ms | 55ms
`1E` | 4ms | 7ms | 4ms | 37ms
`1F` | 2ms | 3.5ms | 2ms | 18ms
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reference: [Super Famicom Development Wiki ](https://wiki.superfamicom.org/spc700-reference#dsp-voice-register:-gain-1156 )
## noise frequencies
value | freq. | value | freq.
----: | -----: | ----: | -------:
`00` | 0 Hz | `10` | 500 Hz
`01` | 16 Hz | `11` | 667 Hz
`02` | 21 Hz | `12` | 800 Hz
`03` | 25 Hz | `13` | 1.0 KHz
`04` | 31 Hz | `14` | 1.3 KHz
`05` | 42 Hz | `15` | 1.6 KHz
`06` | 50 Hz | `16` | 2.0 KHz
`07` | 63 Hz | `17` | 2.7 KHz
`08` | 83 Hz | `18` | 3.2 KHz
`09` | 100 Hz | `19` | 4.0 KHz
`0A` | 125 Hz | `1A` | 5.3 KHz
`0B` | 167 Hz | `1B` | 6.4 KHz
`0C` | 200 Hz | `1C` | 8.0 KHz
`0D` | 250 Hz | `1D` | 10.7 KHz
`0E` | 333 Hz | `1E` | 16 KHz
`0F` | 400 Hz | `1F` | 32 KHz
reference: [Super Famicom Development Wiki ](https://wiki.superfamicom.org/spc700-reference#dsp-register:-flg-1318 )
# resources
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- [SNES-format BRR samples ](https://www.smwcentral.net/?p=stion&s=brrsamples ) at SMW Central
